The Potential of Whole Body Vibration Training during 14

Transcrição

Aus dem Institut für Trainingswissenschaft und Sportinformatik
der Deutschen Sporthochschule Köln
Geschäftsführender Leiter: Prof. Dr. Dr. h.c. mult. Joachim Mester
The Potential of Whole Body Vibration Training during
14-Days of 6°-Head Down Tilt Bed Rest to Counteract Effects
on Muscle Performance, Balance and Articular Cartilage
von der Deutschen Sporthochschule Köln
zur Erlangung des akademischen Grades
Doktorin der Sportwissenschaft
genehmigte Dissertation
vorgelegt von
Dipl. – Sportwiss. Anna-Maria Liphardt
aus Eschwege
Köln 2008
Erster Gutachter:
Univ.-Prof Dr. Dr. h.c. mult. Joachim Mester,
Institut für Trainingswissenschaft und Sportinformatik,
Deutsche Sporthochschule Köln
Zweite Gutachterin: PD Dr. Martina Heer,
Institut für Luft- und Raumfahrtmedizin,
Deutsches Zentrum für Luft- und Raumfahrt, Köln
Vorsitzende des Promotionsausschusses: Univ.-Prof.’in Dr. Ilse Hartmann-Tews
Tag der mündlichen Prüfung: 21. Juli 2008
Erklärung gemäß § 5 Abs. 3: Diese Dissertation wurde an noch keiner anderen Stelle zum
Zwecke der Promotion vorgelegt
Köln, den 30.01.2008
___________________________________________________________________
Dipl.-Sportwiss. Anna-Maria Liphardt
Erklärung gemäß § 5 Abs. 4: Vor diesem angestrebten Promotionsverfahren habe ich keine
anderen Promotionsversuche begonnen und keine Promotionsversuche sind fehlgeschlagen.
Köln, den 30.01.2008
___________________________________________________________________
Eidesstattliche Versicherung:
Hierdurch versichere ich an Eides Statt: Ich habe diese Arbeit selbständig und nur unter
Benutzung der angegebenen Quellen angefertigt; sie hat noch keiner anderen Stelle zur
Prüfung vorgelegen. Wörtlich übernommene Textstellen, auch Einzelsätze oder Teile davon,
sind als Zitate kenntlich gemacht worden.
Köln, den 30.01.2008
___________________________________________________________________
meinem Vater
Content
1
Introduction ......................................................................................................... 1
2
Background......................................................................................................... 3
2.1
2.1.1
Microgravity ............................................................................................ 3
2.1.2
Ground Based Models............................................................................ 4
2.2
Humans in Space – Physiological Effects .................................................. 6
2.2.2
Skeletal Muscle Performance................................................................. 7
2.2.3
Balance .................................................................................................. 8
2.2.4
Cartilage ................................................................................................. 8
2.3
3
Microgravity and Ground Based Models .................................................... 3
Vibration Training ..................................................................................... 10
2.3.1
Physics of Vibration .............................................................................. 10
2.3.2
Mechanical Properties of the Human Body .......................................... 12
2.3.3
Classification of Vibration Training ....................................................... 12
2.3.4
Biological Adaptation to Vibration Training........................................... 14
2.4
Health Risks ............................................................................................. 23
2.5
General Hypotheses................................................................................. 26
General Methods .............................................................................................. 29
3.1
Study Design ............................................................................................ 29
3.2
Study Location.......................................................................................... 31
3.3
Population ................................................................................................ 31
3.3.1
Recruitment Process ............................................................................ 31
3.3.2
Subjects................................................................................................ 32
3.4
Vibration Training Intervention ................................................................. 33
3.4.1
Vibration Training Devise ..................................................................... 33
3.4.2
Vibration Training Protocol ................................................................... 34
3.5
Diet ........................................................................................................... 36
4
3.5.1
Meal Schedule...................................................................................... 36
3.6.1
Nutrient Intake ...................................................................................... 36
3.6
Environmental Conditions ........................................................................ 37
3.7
Physiotherapy........................................................................................... 37
3.8
General Statistics ..................................................................................... 37
Muscle Performance ......................................................................................... 40
4.1
4.1.1
Immobilization / Spaceflight.................................................................. 40
4.1.2
Countermeasures ................................................................................. 42
4.1.3
Vibration Training ................................................................................. 42
4.1.4
Purpose of the Study and Hypotheses ................................................. 44
4.2
Specific Methods ...................................................................................... 45
4.2.1
Muscle Performance Testing................................................................ 45
4.2.2
Statistical analyses ............................................................................... 47
4.3
Results ..................................................................................................... 48
4.4
Discussion ................................................................................................ 50
4.4.1
5
Specific Background................................................................................. 40
Limitations of the Design ...................................................................... 53
Balance ............................................................................................................. 55
5.1
5.1.1
General Physiology .............................................................................. 55
5.1.2
Adaptation during Spaceflight and Immobilization................................ 57
5.1.3
5.1.4
5.2
Methods.................................................................................................... 63
5.2.1
Posturomed® Device ............................................................................ 63
5.2.2
Test Protocol ........................................................................................ 65
5.2.3
Statistics ............................................................................................... 67
5.2.4
Association with Data Loss................................................................... 68
5.2.5
Malfunction of the Sensors of the ‘Posturomed®’ ................................. 68
5.3
5.3.1
Holding Time ........................................................................................ 69
5.3.2
Displacement of the Platform ............................................................... 70
5.3.3
Correlation of the Parameters Displacement and Holding Time .......... 72
5.4
6
Results ..................................................................................................... 69
Discussion ................................................................................................ 73
5.4.1
Limitations of the Design ...................................................................... 77
5.4.2
Conclusion and Future Work ................................................................ 78
Cartilage Health ................................................................................................ 79
6.1
6.1.1
Cartilage Morphology and Loading....................................................... 79
6.1.2
Cartilage Oligometric Matrix Protein..................................................... 80
6.1.3
6.1.4
6.2
Specific Methods ...................................................................................... 83
6.2.1
MR-Imaging .......................................................................................... 83
6.2.2
Three-dimensional (3D) Cartilage Model.............................................. 83
6.2.3
Cartilage Thickness Measurement ....................................................... 84
6.2.4
Blood .................................................................................................... 84
6.2.5
Statistical Analysis................................................................................ 84
6.3
Results ..................................................................................................... 85
6.3.1
Cartilage Thickness .............................................................................. 85
6.3.2
Serum COMP Concentration................................................................ 86
6.4
Discussion ................................................................................................ 88
7
General Discussion........................................................................................... 92
8
Summary........................................................................................................... 95
9
Zusammenfassung ........................................................................................... 98
10
References .................................................................................................... 101
11
APPENDIX – Publications related to the VBR-Study .................................... 112
12
Danksagung .................................................................................................. 114
13
Curriculum Vitae............................................................................................ 116
1 Introduction
1
1
Introduction
Planning and executing of manned interplanetary missions are two of the most
challenging and important tasks in space life science over the next thirty years. The
technical development of space crafts, capable of transporting humans to the Moon
or Mars, will be a monumental task. Additionally, strategies must be developed to
enable humans to live in space for an extended period of time allowing traveling to
another planet and back to Earth.
A microgravity environment is generated by a lack of gravitational forces and by
inactivity generally of the whole body and specifically the lower extremities. This
leads to adaptation processes that are of catabolic nature in the musculoskeletal
system. Currently, the duration of a regular shift for a crew member on board the
International Space Station is about six months. The longest manned mission to
date lasted 437 days which is approximately only one half of the length of a future
mission to Mars. Although training regiments during space flight are continually
improving, the deconditioning in microgravity cannot yet be avoided. Consequently,
the quest for optimized exercise regiments remains a continuous process with the
ultimate goal to develop a training protocol that is not only intense but also short in
duration while affecting as many structures and tissues as possible, mainly the
musculoskeletal system but also the cardio-vascular system.
Whole body vibration training has been proposed as an amendment to traditional
strength training in the past decade. There is scientific evidence to support the
stimulation of the anabolic processes in skeletal muscle and bone. However, many
positive effects have been stated so far without scientific approval or evidence.
Weight based strength training is not applicable in space, as dumbbells are also
weightless in microgravity. In contrast, whole body vibration could technically be
applied in space as it functions on the basis of acceleration of mass. Since technical
developments for space flight are rather expensive, the effectiveness and feasibility
of innovative and improved training methods are usually determined in ground
based models prior to technical developments being finalized for implementation in
space.
The purpose of this doctoral thesis is to test the potential of whole body vibration
training to counteract the effects of 14-days of head down tilt bed rest on the human
body with a focus on the musculoskeletal system. At the Institute of Aerospace
Medicine of the German Aerospace Centre (DLR) in Cologne, Germany, a bed rest
1 Introduction
2
study was performed to test the integrative effect of vibration training during a period
of immobilization.
Specifically, a series of experiments were performed to investigate the effects of
vibration training on the morphology of skeletal muscle, bone and knee cartilage, the
performance of balance and the cardio-vascular system.
Following the introduction, chapter 2 will give a general background on the effects of
microgravity on the human body and describe the current knowledge on vibration
training. Chapter 3 describes the overall hypothesis and the methods followed by
the specific experiments in chapters 4 to 6. These particular chapters that deal with
skeletal muscle, balance and articular cartilage, respectively, will include a specific
introduction to the field, followed by the specific hypotheses, methods, results and
discussion. The results presented in these chapters will be consolidated in the
general discussion presented in chapter 7.
2 Background
3
2 Background
2.1
Microgravity and Ground Based Models
2.1.1 Microgravity
Gravity is the force that affects all motion on earth and in space. In 1687, Sir Isaac
Newton described for the first time the nature of gravity as the attraction of two
masses towards each other. Gravitational force is defined as the product of the
gravitational constant and the mass of an object. On earth, the constant
acceleration, also called normal gravity is 9.81m/s² or 1g. It describes the
acceleration of an object by gravity alone without any external influence. Gravity is
the reason why we stand on the ground and why objects fall down. It is also the
force that causes the Moon, satellites and also the International Space Station (ISS)
to orbit Earth. Microgravitational conditions are the result of a free fall at the
acceleration of 1G. The International Space Station orbits earth at a height of about
400 km where the gravitational field is still 88.8% of 1G. This is the force that is
necessary to keep it orbiting around the Earth. The microgravity conditions on board
the spacecraft are caused by the continuous free fall of the space craft around our
Planet (Figure 2.1).
Figure 2.1: Mechanism of microgravity caused by a free fall around Earth
The International Space Station and all objects, including the astronauts inside it, fall
at the same speed around Earth and this is perceived as “weightlessness”. The
2 Background
4
approximate speed that is necessary to create a free fall around Earth is 28.000
kilometers per hour. Since gravity is not zero but approximately 1x10-6 g we use the
term microgravity rather than weightlessness.
Microgravity can be created whenever an object is in free fall. Therefore, in addition
to missions in space flight research with shuttles or the International Space Station,
microgravity can also be associated with parabolic flights, sounding rockets or drop
towers.
Gravity plays a major role in our daily life on Earth. We are used to the fact that
objects fall down and if we ‘lose’ something, we search the floor to find it. But how
do you change your strategy searching a three dimensional space without the
presence of normal gravity? While this reflects a major practical challenge, the
human organism and its evolution have also been strongly influenced by gravity.
When humans travel to space, the body rapidly adapts to the change in gravitational
force. Motion Sickness and Puffy Face are two phenomena that can be observed
very early during a space mission and this is followed by a huge number of
adaptation processes in the human body that are caused by the lack of gravity.
Generally, degradation of physiological processes and atrophy of several different
tissues are observed. They reflect a natural adaptation to the microgravity
environment which in turn can lead to health problems upon the return to the Earth
environment. Since the early days of space flights, astronauts have been subjects
for life science research with the aim to reduce the risks of space flight and to
develop countermeasures in order to decrease the rate of degradation.
2.1.2 Ground Based Models
As the number of subjects traveling to space is very limited, ground based models
that simulate the effect of microgravity on the human body were developed in order
to explore the response of the human body to immobilization and to develop
adequate countermeasures. It is important to note that microgravity itself cannot be
simulated except during free fall. During Parabolic Flights, time frames of
approximately 30 seconds of microgravity can be achieved, which is too short to
simulate physiological processes that occur during a space mission.
Immobilization using bed rest has been shown to be a highly feasible model to
simulate effects of microgravity on the musculoskeletal system. As described in the
recent review: ‘From space to Earth: advances in human physiology from 20 years
of bed rest studies.’ (Pavy-Le Traon et al., 2007), sitting on a chair or being
2 Background
5
immersed in water have also been used to simulate inactivity and the lack of
gravitational forces. Water immersion is still used as a model in space flight studies
because it can better simulate the lower gravitational forces acting on the human
body than bed rest. However, water immersion studies involve a number of risks
because the skin must be kept dry which creates a very complex experiment setting.
The bed rest model has been generally accepted as the standard model for
simulating the effects of microgravity for many physiological systems, particularly the
musculoskeletal system. A bed rest model has been used by “Space Flight Nations“
for research purposes since the 1960’s. Russian researchers concluded from a
study that bed rest at 6° head-down-tilt simulates more realistically the feeling to be
in space (Kakurin et al., 1976; Pavy-Le Traon et al., 2007). Since that time 6°-head
down tilt bed rest (6°-HDT bed rest) has been used to induce the effects of
microgravity on the human organism and is now called the gold standard.
However, ground based models can simulate only some of the physiological effects
that occur under microgravity. Parts of the mechanisms that lead to these
physiological effects may not be the same on the ground and in microgravity.
Microgravity is a unique condition and a ground based model with its underlying
assumptions can only try to replicate, as much as possible, the effects of spaceflight
on the human organism.
Bed rest studies can also be used to simulate physiological and pathophysiological
adaptations of the human body due to a sedentary lifestyle, longer-term
immobilization due to illness and/or injury or reduced mobility in aging. The
advantage of bed rest studies is that they are conducted in a tightly controlled
environment. In contrast to field studies, measures such as nutrient intake, fluid
intake and exercise can be standardized and controlled making it possible to
investigate the ‘isolated’ effect of unloading.
2 Background
2.2
6
Humans in Space – Physiological Effects
2.2.1 Physiological Effects of Microgravity
The human body requires a certain amount of physical activity in a gravitational
environment to maintain a healthy physical status of its various physiological
systems. Changes in the demands on the human body can lead to physiological
adaptations that enable the body to meet the new requirements. Athletes use this
plasticity of the body’s “active” biological tissues, such as muscle mass, for instance
by increasing the load during resistance training in order to achieve higher
performance levels after several weeks of training.
Space flight presents a complex challenge for the human body. The great variety of
physiological adaptations of the human body due to the microgravity environment
that affect, for instance, the musculoskeletal system, the cardio-vascular system, the
immune system and fluid regulation can be observed during and after the
astronauts’ stay in sapce. These adaptations of the body during a period in
microgravity provide an excellent opportunity to investigate the impact of normal
constant gravity on its physiological status (Convertino, 1996). Additionally, in terms
of energy expenditure, the activity level in space is reduced when compared to daily
life on earth. Particularly, since the use of the lower extremity is not necessary for
locomotion, the accompanied reduction in energy expenditure should contribute to
the major functional changes of the musculoskeletal system of the lower extremity.
In the following, the effects of microgravity on different tissues and organs of the
human body are described with a specific focus on skeletal muscle, balance and
cartilage since these tissues and processes were investigated in this doctoral thesis.
In general, the physiological effects are investigated under 1G conditions prior to the
space mission and after returnning of the astronauts to Earth. The physiological
changes caused by a microgravity environment normally do not harm the astronauts
or limit them in their actions as long as they stay in microgravity. Also, they usually
are not “pathological” in a space environment. However, once astronauts return to a
gravitational environment, such as Earth (or Mars or Moon in the future), they may
experience more or less serious health problems. While this may be of little concern
when they return to Earth since they can receive adequate medical support, there
could be major concerns regarding the astronauts’ safety during interplanetary
missions.
2 Background
7
2.2.2 Skeletal Muscle Performance
The skeletal muscles major tasks on earth are to facilitate the body’s upright position
and enhance locomotion. The muscles move objects, for instance masses, against
gravity. In microgravity, this force is lacking which means a reduced effort for
locomotion and consequently leads to disuse induced atrophic processes in skeletal
muscles. As a response to the change of demands by microgravity, there is a
physiological adaptation of muscle in terms of structure as well as function. The so
called anti-gravity muscles of the lower extremity are mainly affected by microgravity
since the difference in load for these muscles is greater than for arm and trunk
muscles. Decreased muscular performance limits their physical activity for a certain
period of time once they return to a gravity environment such as Earth or Mars.
Loss of strength has been measured for different muscle groups of the body in
microgravity (Kakurin et al., 1976; Kozlovskaya et al., 1981; Thorton and Rummel,
1977) and it affects both maximum strength and power. Thorton et al. (1977)
concluded that microgravity reduced muscle strength primarily in the lower
extremity. They further stated that the rate of loss in muscle strength was directly
linked to a reduction of body weight and leg muscle volume during the flight and was
inversely related to the amount of in-flight training performed by the astronauts.
When analyzing space flight results it has to be taken into account, that for example
NASA flight rules require that crew members must exercise if the flight duration is
longer than 10 days (Adams et al., 2003). This would lead to an underestimation of
the actual effects that microgravity alone would have on skeletal muscle. In addition,
discrepancies between the results of, for instance, Russian and American Missions
could be partly explained by these different rules.
To date, it is not known whether the high variability of microgravity effects between
astronauts is caused by different in-flight countermeasure treatments or is a true
difference in the sensitivity of skeletal muscle to microgravity (Fitts et al., 2000; Fitts
et al., 2001; Lambertz et al., 2001; Zange et al., 1997). Further, it is acknowledged
that data collected during space flight are rare and that the level of control of factors
including, for instance pre-flight training level, in-flight training intensity or nutrition, is
limited. Usually, the primary aim of space missions is not to conduct a physiological
study. Rather, in the past, physiological studies were often performed as a side
product because of the scarcity of ‘free time’. Further, the motivation and opportunity
to exercise during a mission differ between astronauts and missions. During space
flight, no comparable atrophic effects could be investigated for the arm muscles.
2 Background
8
This may be due to the fact that, first of all, astronauts use the arms in microgravity
for locomotion inside the shuttle or space station and also when they perform
experiments during the flight. Secondly, the differences in requirements in 1G
conditions compared to microgravity conditions are not as pronounced for the arms
which may result in less muscle atrophy. This might also indicate the impact of the
pre flight activity levels on the adaptation of skeletal muscles to the microgravity
environment.
The specific background in chapter 4 -Muscle Performance – will provide more
details on changes in skeletal muscle due to microgravity.
2.2.3 Balance
During spaceflight, the demands on the lower extremity muscles are reduced to a
minimum which not only leads to changes in muscle performance but also affects
the ability to stabilize body position when astronauts return to Earth. Peripheral and
central neural processes of postural control are physiologically and functionally
altered when astronauts return from a stay in microgravity (Clement et al., 2005).
Although postural control is important for the operational performance during a
space mission, the focus of this study will be on changes in postural body control
after a period of immobilization which is comparable to the return of astronauts into
a gravity environment, such as Earth, the Moon or Mars. Astronauts then show a
reduced ability for postural control together with less muscle performance which can
pose a major safety problem or risk of injury. This is especially important for future
interplanetary missions, where astronauts cannot always rely on physical support
from team members on Earth. Consequently, the effects of microgravity on balance
should be assessed and appropriate countermeasures should be considered in
order to minimize these safety issues and risks of injury.
Details of the effects of microgravity on balance will be introduced in chapter 5 Balance.
2.2.4 Cartilage
Articular cartilage in synovial joints serves a variety of functions, including providing
joint congruency, transferring and distributing forces, and allowing joint movement. A
healthy biological and mechanical environment of cartilage is the prerequisite for
proper joint function. Cartilage, like other biological tissues including skeletal muscle
and bone, is sensitive to loading and disuse (Johnson, 1998; Smith et al., 1992a).
2 Background
9
Typically, a change in the biological and/or mechanical environment of cartilage
leads to cartilage degeneration or osteoarthritis. While the role of mechanobiological
factors for healthy cartilage development and maintenance have received much
attention (Carter and Wong, 1988a; Wong et al., 1999; Wong and Carter, 1988) the
effects of space flight or immobilization and partial weight bearing after injuries on
cartilage biology and morphology in man are largely unknown.
Some animal studies (Haapala et al., 2000; Jurvelin et al., 1986; Kiviranta et al.,
1988a) have shown decreases in cartilage thickness and cartilage stiffness in dogs
after 11 week of immobilization whereas other studies found no changes in
proteoglycan and collagen content, cartilage stiffness or cartilage thickness (Setton
et al., 1997) after immobilization of canines. The discrepancy of these results may
be due to the fact that the type of immobilization plays a role in the potential of the
cartilage to recover (Behrens et al., 1989) .Only few studies (Eckstein et al., 2000;
Eckstein et al., 2002a; Eckstein et al., 2002b; Eckstein et al., 2005; Helminen et al.,
2000; Hinterwimmer et al., 2004; Hudelmaier et al., 2003; Muhlbauer et al., 2000;
Vanwanseele et al., 2002; Vanwanseele et al., 2003) have investigated the influence
of unloading on articular cartilage in humans so far. Studies on human articular
cartilage in the scope of space flight research have, to the best of our knowledge,
not been performed so far.
Specific details on the sensitivity of articular cartilage and biomarkers of cartilage
health will be given in chapter 6 -Cartilage Health.
2 Background
2.3
10
Vibration Training
Scientists have investigated the effects of vibration on the human body for many
years. Most frequently, vibrations were studied in the context of occupational
medicine and considered as ‘negative’. For instance, by damping seats in trucks and
cars, health risks potentially arising from vibration have been minimized. The
potential danger of the application of vibrations to the human body can not be
neglected and will be discussed in chapter 2.5.
Nevertheless, in the past decade, vibration training has become very popular as a
complement to regular strength training (Jordan et al., 2005) in an attempt to
increase the efficiency of strength training that may affect all tissues of the
musculoskeletal system. Current research is conducted to find the optimal
combination of different variables such as training intensity, frequency and
amplitude of the vibration, mechanical characteristics of the vibration input and
others that would result in a positive response in terms of an anabolic reaction in
training processes. An increasing number of studies investigating the effects of
vibration are being published each year and the results describing all facets of
vibration training, most frequently the effect on muscular performance, have been
published in various reviews (Cardinale and Wakeling, 2005; Issurin, 2005; Jordan
et al., 2005; Luo et al., 2005; Mester et al., 1999b; Mester et al., 2001; Mester et al.,
2006; Nordlund and Thorstensson, 2007; Rehn et al., 2007).
This chapter will deal with the physics of vibration and the human body, followed by
the known effects of vibration training on the musculoskeletal system, possible
underlying physiological mechanisms and health risks.
2.3.1 Physics of Vibration
Vibration has been defined as the motion of a particle which oscillates about its
position of equilibrium (Beer and Johnston, 1987). Vibrations can be divided into
deterministic and stochastic vibrations and can be classified as shown in Figure 2.2.
Only with a sinusoidal vibration is it possible to study the response to a single
frequency of motion (Griffin, 1996). Consequently, studies on the human response
to vibrations usually use the reactions to pure sinusoidal vibrations. Vibration studies
investigating vibration exposures of people during work, travel or leisure are often
described as random vibrations.
2 Background
11
Figure 2.2: Classification of Vibrations of different types of oscillatory motion (Griffin, 1996)
Vibrations can be described by the parameters of amplitude, frequency and
magnitude. The amplitude of the displacement of the vibration is determined by the
extent of the oscillation and the frequency by the repetition rate of the cycles of the
oscillation. The measure for frequency is cycles per second (s.p.s.) and the unit is
‘Hertz’ (Hz). The simplest type of motion contains only one frequency and would
2 Background
12
occur when there is a sinusoidal oscillation at only one frequency. Normally, the
human body is exposed to more than one frequency. The response to vibration
exposure is highly dependent on the frequency content of the vibration.
The magnitude of the displacement of oscillatory movements can be measured in
many different ways. First, it can be described as the difference between the
maximum displacement in one direction and the maximum displacement in the
opposite direction. However, displacement is only useful to describe large-amplitude
and low frequency vibrations. Secondly, the magnitude of the oscillation can also be
described by its velocity; a quantity that is related to the energy of the vibration.
Thirdly, the magnitude of oscillations can be described by its acceleration. The
acceleration is expressed in meters per second per second (m/s ² or m*s-²) (Griffin,
1996).
2.3.2 Mechanical Properties of the Human Body
Knowledge of the mechanical properties of the human body is important when
investigating the effects of vibrations. They help to estimate the physiological and
pathological effects that can be expected when the body is exposed to vibrations.
Knowing the mechanical properties also allows the biomechanical interpretation of
physiological responses caused by vibrations (Hauptverband der gewerblichen
Berufsgenossenschaften (Edt.), 1984).
The human body can be described as a damped-free-vibrating system and the
model that is usually used is a spring-mass-model. However, the human body is a
system with many different tissue properties which lead to different spring constants
and damping properties (i.e. muscles, ligaments, tendons, fat tissue bones and
others). Other variables, such as the masses of bones and other tissues, are difficult
to measure and may change due to different muscle activity (Hauptverband der
gew. BG (1984); (Rasmussen, 1983)).
2.3.3 Classification of Vibration Training
In the past decade, vibration training has evolved into a well known and wide spread
training method. The use of vibrations in isometric strength training was first
developed in Russia where training devices were used to transmit vibrations to the
muscle belly (Cardinale and Wakeling, 2005; Nazarov and Spivak, 1985). However,
the physiological consequences of vibration training are not fully understood.
Although very little is known about the mechanisms on how vibration training
2 Background
13
stimulates the human body, the manufacturer of the various commercially available
training devices (e.g. Galileo 2000 or Powerplate) have been advertising and selling
their machines.
When reviewing the literature on vibration training and on the influence of vibrations
on the human body, one should distinguish between whole body vibration training
and vibrations applied directly to the muscle belly or tendon. With regard to the
human body, the vibrations can be classified according to the point of contact with
the human body and on the proportion of the body they affect. The different modes
of vibration training range from whole body vibrations to local or regional vibrations
and can be foot-transmitted, head-transmitted or hand-transmitted vibrations.
Further, whole body vibration can be transmitted to the body while sitting, standing
or lying on the vibrating surface (Griffin, 1996). In sports, the body experiences
various types of vibration such as during alpine skiing, inline skating or cycling.
Where the body receives the vibration and whether it is possible for it to damp the
vibrations or not, determines if they are “good” or “bad” vibrations. More about safety
considerations and criteria for “good” and “bad” will be discussed in chapter 2.4 Health Risks.
The fact that the body is comprised of many different tissues makes the system
more complex and adds to the difficulty in understanding the response of the body
to vibrations (Spitzenpfeil et al., 2000).
Vibrations can also be classified by the type of oscillation produced by different
vibration devices. During whole body vibration training, the subject or athlete usually
stands on a vibration platform that produces oscillation vibrations. Depending on the
position of the subject on the plate, the vibrations are transmitted through the whole
body and even the head can receive a great amount of the mechanical vibration
signal, which must be regarded as one of the most dangerous effects.
The vibration plates that are currently available on the market produce two main
types of signals:
a. alternate acceleration of the left and right leg like a seesaw
b. simultaneous vibration of the whole body
So far there is no evidence, that one plate elicits better training responses than the
other although the different companies say so.
Many different companies offer their latest development of vibration plate such as
for example:
-
the Nemes Bosco System®, OMP, Rieti, Italy;
2 Background
-
14
Galileo 2000® device and Space Galieleo®, Novotec Pfortzheim,
Germany,
-
Powerplate® North America Inc., Northbrook, IL, USA,
-
VibroGym® , ES Haarlem, The Netherlands
Not only the characteristics of vibration as an input signal can be classified but also
the effect vibration elicits in the human body.
The effects of vibrations on the human body can be divided into ‘mechanical effects’
and ‘biological effects’. Mechanical effects describe the resonance and damping
properties of the human body. Biological effects deal with the respiratory, cardiovascular and neuro-muscular effects of vibration on the human body (Cole, 1982).
However, in practical applications it will be difficult to distinguish between the two as
it is not possible to apply vibration to a living organ and only elicit biological or
mechanical effects. Additionally, Griffin (1996) defines effects on comfort, physical
activity and health of the person. The following chapters however, will deal with the
biological adaptation of the body to vibration training.
2.3.4 Biological Adaptation to Vibration Training
2.3.4.1
Neurophysiological Effects
Although there is increasing interest in vibration training as a tool for rehabilitation,
training or prevention, knowledge about the physiological processes that vibration
training elicits is still limited. This is mainly due to the very complex input signal
caused by the vibration and the complexity of the human/animal body. Usually,
investigator groups are not able to account for all possible effects generated by
vibration. Consequently, each study only gives limited insight into the actual effect
vibration may have on the body.
In most of the studies investigating the training effects of vibration training, neural
adaptations to the vibration stimulus are expected. If a muscle is vibrated, this
stimulates the primary endings of the muscle spindle which consequently excites the
α-motoneurons and leads to muscle contraction. This tonic contraction of the muscle
has been described by Eklund and Hagbarth (Eklund and Hagbarth, 1966) as the
tonic vibration reflex (TVR). In their experiments they applied high frequency
vibrations directly onto the tendon which led to a contraction of muscle and the
relaxation of the antagonist
(Eklund and Hagbarth, 1966; Mester et al., 2001).
However, the involvement of the tonic vibration reflex during vibration training has
2 Background
15
not yet been experimentally proven and it has not been shown how such a
mechanism would cause a positive effect on muscle performance (Mester et al.,
2001; Nordlund and Thorstensson, 2007).
The tonic vibration reflex can actively be influenced by higher cortical centers of
motor control and it has not yet been shown whether mono-synaptic or polysynaptic
pathways are dominantly used for signal transmission through the body (Mester et
al., 2001).
Usually, in whole body vibration training, the mechanical input is applied through the
feet and other receptors than the muscle spindles are also stimulated such as for
example the Golgi-tendon organs. In the experiments of Eklund and Hagbarth
(1966), only the tendon was stimulated; whereas in vibration training, both the
tendons and muscle are likely to be stimulated through vibration. Thus, there may
very well be an overlap of several mechanisms that stimulate various receptors.
Nordlund et al. (Nordlund and Thorstensson, 2007) criticize the use of the tonic
vibration reflex as an explanation for the positive findings of vibration training. First
they state, that the tonic vibration reflex was demonstrated in a very different setting
from vibration training since the time of exposure was only 30s and the frequency
was higher than normally used in vibration training. Also, they put forth the criticism
that later experiments where vibration was directly applied to the muscle and a
decrease in muscle activity was reported (Bongiovanni et al., 1990; Ribot-Ciscar et
al., 1998) are often not considered in the discussion about the effects of vibration
training. Additionally, they noted that muscle spindle firing also causes inhibition of
the antagonistic muscles via reciprocal inhibition (Crone and Nielsen, 1994) and
thus a prediction of the actual activation level during the exposure to vibration would
be difficult (Nordlund and Thorstensson, 2007). They suggested that for an assumed
increased level of muscle activation during whole body vibration, the training would
have to cause an increase in the ability to maximally activate the agonistic muscle
and/or to improve inter-muscular coordination (e.g., decrease the activation of the
antagonistic muscles). Nordlund et al. (2007) also questioned the theoretical
benefits of whole body vibration training on coordinative performance as, from their
perspective, the training method lacks specificity. They concluded that there was no
evidence for justifying a recommendation of whole body vibration as a replacement
or addition for strength training.
2 Background
2.3.4.2
16
Muscle Performance
The term muscle performance comprises a wide range of parameters that can be
measured. The parameters one can measure in the context of skeletal muscle
performance are as diverse as the studies that have been published on the effects
of vibration training.
During whole body vibration training, the subject performs isometric or dynamic
exercises on a vibrating platform. In addition, the regular parameters such as
intensity, repetitions and amount of series of a specific exercise, training protocols
for vibration training can be adjusted in frequency and amplitude. Various vibration
frequencies between 15 Hz and 90 Hz have been used to achieve adaptations in
skeletal muscle or bone (Issurin, 2005; Rubin et al., 2002a). For safety reasons (see
also chapter 2.4), it has been suggested to exercise only on the vibration plate with
flexed knees, as this position minimizes the transmission of vibrations to the head
(Cardinale and Rittweger, 2006).
One can either measure the acute effects of vibration training, i.e., during or right
after the application of the training, or the long-term effects. However, there is no
clear-cut definition what is “acute” or “short-term” and what is “long-term”. The
results after two weeks of vibration training can be considered long term when
compared to measurements taken after a single bout of vibration. On the other
hand, the results after two weeks can be taken as acute or short-term effects when
compared to a six month vibration training intervention. Regardless whether acute or
long term effects were studied, the published results have so far been controversial.
Torvinen et al. for instance showed an increased jump height and isometric knee
force (Torvinen et al., 2002a) after 4 minutes of vibration training. Other studies
looking at the acute effects of vibration training found a decline in muscular
performance (De Ruiter et al., 2003; Torvinen et al., 2002a). Studies on long-term
effects of vibration training revealed that vibration training could be beneficial for
muscle performance. Several studies showed positive training effects on muscle
strength and power (Issurin et al., 1994; Issurin and Tenenbaum, 1999; Liebermann
and Issurin, 1997; Mester et al., 1999a). Increased performance after the exposure
to whole body vibration could be the result of an improved synchronization of motor
units and an improved co-contraction of the synergistic muscles (Haleva, 2005;
Jordan et al., 2005). More details on the effect of vibration training on muscle
performance will be presented in chapter 4 - Muscle Performance.
2 Background
2.3.4.3
17
Balance
Since the application of vibrations to the human body activates the neuro-muscular
system (Haas et al., 2004), it should also influence the coordination of movement.
Without affecting the coordinative portion of movement, vibration training would not
be able to enhance muscle performance. Additionally, there are certain receptors,
especially in the cutaneous tissue, that sense vibratory movements and hence
certainly will be affected by vibration training (for more details see chapter 5.1.1).
Studies on the effects of vibration training or vibration stimuli on balance and
coordinative processes have been performed mostly in medical environments. Such
examples as in the context of rehabilitation of orthopedic injuries (Berschin and
Sommer, 2004) and the prevention of fall risk (Bautmans et al., 2005; Bruyere et al.,
2005; Kawanabe et al., 2007) have produced promissing results.
Also, vibration training becomes popular as a training method for the treatment of
neurological diseases such as Parkinson disease (Haas et al., 2004; Turbanski et
al., 2005) or Multiple Sclerosis (Schuhfried et al., 2005) and injuries resulting in
paraplegic patients (Melchiorri et al., 2007). More details on the effect of vibration
training on balance performance will be presented in chapter 5 - Balance.
2.3.4.4
Cardio-Vascular-System
Since the cardio-vascular system serves as a ‘supplier’ for muscle and bone it
should also be affected as soon as vibration training affects the human body.
Additionally the vascular system that is close to the source of vibration should be
affected from the mechanical input signal since the vessels are vibrated as well with
the rest of the body. Therefore, this chapter will deal with the effects of training on
the cardio-vascular-system on the one hand and with direct effects on the vessels
on the other hand.
2.3.4.4.1 Endurance Performance
Rittweger et al. (Rittweger et al., 2000) showed an oxygen uptake of less then 50%
of VO2 max during cycle ergometry when performing whole body vibration training to
exhaustion. Additionally, systolic arterial blood pressure increased after vibration
training whereas diastolic blood pressure decreased. The reason for the decrease in
diastolic blood pressure could have been arterial vasodilatation that could be
accounted for by changes in muscular perfusion. They suggested that exhaustive
whole body vibration elicits only a mild cardio vascular exertion and that neural as
2 Background
18
well as muscular mechanisms may play a role in the functioning of vibration training.
Also vibration training led to erythema, swelling or itching in some subjects
(Rittweger et al., 2000) which might have been caused by an increased cutaneous
blood flow (Cardinale and Rittweger, 2006). Overall, the observed very mild
cardiovascular effect led them to conclude that this training method was well
applicable in the elderly as it did not stress them into exhaustion.
In a study by Kerschan-Schindl (Kerschan-Schindl et al., 2001), it was shown that
muscle blood volume increased in the calf and thigh during whole body vibration
training at 26Hz. In their study, blood pressure did not change with vibration training.
As previous studies have produced contradictory results at much higher frequencies
(Lundström&Burström 1984, Bovenzi&Griffin 1997), the authors concluded that the
circulatory response was highly dependent on the magnitude as well as the vibration
frequency. Also, the group showed an increase in blood flow in the popliteal artery
suggesting that vibration training reduced the viscosity of blood and thus increased
it’s velocity through the arteries.
More recent studies published by Rittweger (Rittweger et al., 2001; Rittweger et al.,
2002) showed that the metabolic power of skeletal muscle was enhanced during
vibration training and could be controlled by frequency and amplitude of the
vibration, as well as by the application of additional loads.
Cardinale et al. (Cardinale and Wakeling, 2005) suggested that the above
mentioned studies indicated a mild effect of vibration training on the cardiovascular
system. However, they concluded that the stimulus of whole body vibration would be
too low making it unlikely that athletes would benefit from it as a new training
method. However, it has to be taken into account that the training design choosen
by Rittweger and Kerschan-Schindl was not used to enhance endurance
performance. Adding whole body vibration on a cycle ergometer or on a treadmill
may produce better results for the cardio-vascular system. Suhr et al. (Suhr et al.,
2007) could show, for example, that high intensity cycling under vibration conditions
could enhance the concentration of vascular endothelial growth factor (VEGF). The
results suggested a positive effect of vibration training on the angiogenesis.
2.3.4.4.2 Energy Expenditure
Only a few studies addressed the effect of vibration training on energy expenditure
of vibration training. Rittweger et al. (2002) reported that metabolic power increased
with vibration training. They stated after VO2max measurements with and without
vibration that energy requirements during vibration training were as high as during
2 Background
19
moderate walking and that this could even be increased with increasing frequency
and amplitude of the vibration signal (Rittweger et al., 2002). Da Silva et al. (Da
Silva et al., 2007) investigated the effects of vibration training used for hypertrophy
training on energy expenditure. They found that application of vibration training
during half squatting increased energy expenditure when compared to non-vibration
controls.
2.3.4.4.3 Mechanical Effects on the Cardio-Vascular-System
Studies on cardiovascular effects of vibration training are rather scarce to date. Most
of them are done on animal models.
Murfee et al. (Murfee et al., 2005) found that 6 weeks of vibration training for 15
minutes/day stimulated vascular remodeling in mice, meaning they observed a
decrease of blood vessels per muscle fiber in mouse soleus muscle while the
muscle fibers themselves and the number of muscle fibers did not change. They
were surprised at the results since they were not as expected. However, the authors
pointed out that the vascular remodeling was sensitive to the applied vibration
protocol and the direction of the response could have been altered to an anabolic
response with changing the training intensity.
Yue et al. (Yue and Mester, 2007a; Yue and Mester, 2007b) performed a model
analysis to predict the effects of whole body vibration on the cardiovascular system
and more specifically, the blood vessels in humans. Hydrodynamic analysis showed
that longitudinal vibration of vessels increased the shear stress on the vessel walls,
especially in the larger vessels such as the aorta, larger veins and arteries, and the
coronary artery. They suggested, that this strong mechanical stimulus could be
beneficial because it might elicit endothelial-dependent and nitric oxide-dependent
angiogenesis (Yue and Mester, 2007a). On the other hand, the increased shear
stress could be a potential risk factor when performing vibration training with a
history of diseased coronary or cerebral arteries. The lateral component of the
vibration signal was analysed separately and showed that vibration led to a dilation
of the vessel which significantly decreased the total peripheral resistance (Yue and
Mester, 2007b). The mechanisms underlying that finding seemed to be mechanobiological in nature. The vibration causes motion of the red blood cells which, in turn,
causes them to collide with the walls of the vessels and with each another. These
collisions may induce the release of nitric oxide (NO), a strong vasodilator. The
authors suggested, that vibration training may have been beneficial to improve the
ability of the body to counteract high blood pressures with the vasodilatation (Yue
2 Background
20
and Mester, 2007b). Similar results were published by Mester et al. (Mester et al.,
2006) who found an increase in peripheral resistance during vibration training at
different frequencies compared to pre-training levels. However, after exercise, the
peripheral resistance was lower than the pre-training levels which suggested that
the body compensated for the higher oxygen requirements during training by dilating
the vessels (Mester et al., 2006).
Although the number of studies dealing with the direct effects off vibration training
on the vascular system is small, as opposed to the effects on endurance
performance, the results are similar. The vascular system of the body is sensitive to
even very low mechanical stimulation.
2.3.4.5
Endocrine System
The effect of vibration training on the endocrine system has not been studied in
depth yet. However, some studies in the past years have investigated acute and
long term effects of vibration training on the endocrine system (Cardinale et al.,
2006; Di Loreto et al., 2004; Kvorning et al., 2006b). It has been stated that the
additional gravitational load the subject is exposed to elicits an anabolic hormonal
response (Cardinale and Bosco, 2003). This would be comparable to mechanistic
studies during conventional strength training where evidence evolved that increasing
blood levels of anabolic hormones are positively correlated to both muscle
hypertrophy and muscle strength (Ahtiainen et al., 2003; Kraemer et al., 2002;
Kraemer and Ratamess, 2005).
Some studies have investigated the
acute effect of vibration training on the
endocrine system (Bosco et al., 2000b; Bosco et al., 2000a; Cardinale et al., 2006;
Cardinale and Bosco, 2003; Kvorning et al., 2006a). Bosco et al. (2000) applied 10
minutes of whole body vibration at 26 Hz and 4 mm amplitude to recreationally
active people (Bosco et al., 2000b). They reported acute increases in serum levels
of testosterone and human growth hormone (hGH) and decreases of cortisol levels.
However, as stated by Cardinale et al., their earlier study was missing a control
group; thus, the differences between conventional resistance training and whole
body vibration training remains unknown (Cardinale and Wakeling, 2005).
Recent studies used better control conditions. Di Loreto and Co-Workers (Di Loreto
et al., 2004) hypothesized that vibration training might be a treatment for obesity
because increasing serum levels of hGH and testosterone and concurrent inhibition
of cortisol should have lead to a reduction of fat and augmentation of lean body
2 Background
21
mass; thus reducing fat mass. In order to test their hypothesis they exposed 10
healthy men to 10 x 1 minute of whole body vibration training at 30Hz and
investigated the effect on circulating levels of glucose, insulin, glucagon, hGH, IGF-1
cortisol, epinephrine, norepinephrine and total and free testosterone. However, their
hypothesis could not be confirmed. Although they found slightly reduced plasma
glucose and slightly increased plasma norepinephrine levels, all the other
parameters remained unchanged. Therfore, they concluded that vibration training
transiently reduces plasma glucose, possibly by increasing glucose utilization by
contracting muscle, and increases plasma norepinephrine, possibly by protracted
peripheral sympathetic pathway activation (Di Loreto et al., 2004). They suggested
that the hormonal response of vibration training is not mediating the anabolic effects
of vibration training on bone and muscle. However, it has to be acknowledged that
the intensity of the applied training may not have been high enough as subjects only
stood on the vibration plate and performed a static exercise without additional load.
Kvorning et al. (Kvorning et al., 2006a) reported greater increases in cortisol when
performing squats with vibration than squats alone. Combining conventional
resistance training (squats) with vibration did not increase testosterone levels;
however, it did stimulate a greater response in hGH in the first training. Changes in
hGH and testosterone were similar when squats were performed on a vibration plate
and squats alone. Their decision to generally reject the hypothesis that whole body
vibration training could optimize resistance training and the anabolic hormonal
response to it should be modified in that way that the training protocol they used did
not lead to beneficial effects on the hormonal response to resistance exercise. This
is important to note as there is potential to optimize the time point of testing and
measuring as well as the training intensity itself.
Also, the most recent studies on the anabolic stimulation through vibration training
(Cardinale et al., 2006; Erskine et al., 2007) did not find an increase in testosterone
and IGF-1 levels. They tested the effect of a single session of vibration training on
the hormonal response.
In summary, the hormonal response to vibration training on a systemic level did not
show consistent results yet. Similar to many of the other physiological systems of
the human body, the training intensity has to be tailored much more individually than
it has been done to date and it seems that often intensity levels for the vibration
condition were very often not high enough for the chosen sample of test subjects.
2 Background
2.3.4.6
22
General Performance
To summarize the training effects of vibration training, it is concluded that there is
still no consensus on how vibration training “works” and whether it is a beneficial
method to amend traditional training methods. It appears that there is a lack of
systematic research in the area. Most of the studies are in terms of training intensity
and volume not tailored to any specific training method. For example if the training
includes squats with additional weight there is a training impact on the quadriceps
muscle. However, to find changes in calf muscle performance or in endurance
parameters after that kind of training is unlikely. Therefore, in future studies, the
training protocols should be much more tailored to the muscle or focused on the
system of interest. Jordan et al. (Jordan et al., 2005) stated that the variability in
outcomes of vibration studies may be a result of the differences in the training
protocols. Most of the protocols used thus far, vary in vibration characteristics,
position on the plate, performed exercise on the plate, additional load and others. It
is probable that each of these parameters affects the physiological response to the
applied training. Consequently, there is a need for well controlled studies to explore
further the effects of vibration training.
2 Background
2.4
23
Health Risks
The human body consists of rigid structures, such as bones, and non-rigid
structures such as muscles, fat tissue and other soft tissues such as organs. Every
structure, including biological tissues has resonance frequencies. If a structure is hit
by its resonance frequency this can lead to destruction, not only for example for
bridges but also for tissues. Therefore, vibration exposure is an important issue in
the field of occupational medicine as vibrations often occur in the working
environment (e.g., car seats, jackhammer, chain saw) and can cause discomfort,
injury and disease (Griffin, 2004).
The resonance frequency (natural frequency) varies depending on the mechanical
properties of the structure in question. Bones have resonance frequencies of 200 to
900 Hz (Nigg and Wakeling, 2001) and the resonance frequency of different
muscles ranges between 5 and 65 Hz (Wakeling and Nigg, 2001). If the vibrations
transmitted to the human body overlap with the resonance frequency of the specific
tissue, there may be pathological effects. If the body is exposed to long-term or
high-energy vibrations, this often results in discomfort or even pathological changes
to the nervous and vascular systems (Sakakibara, 1994).
The resonance frequencies for different extremities, including the organs, are
presented in Figure 2.3.
Resonance frequencies depend on the posture of the person when receiving
vibrations as they change with muscle activity (Wakeling and Nigg, 2001). How
exposure to the vibrations can be tolerated also depends on the direction in which
the vibrations act on the human body. The resonance frequencies of muscle are in
the range of the input frequencies the body receives; for example, during the landing
in sport activities such as normal running (Stefanyshyn and Nigg, 2000). Due to the
structural composition of the human body it is difficult to observe how the vibrations
are transmitted through the body (Junghans, 1986) and how they change from the
time when they are introduced to the body to the time they are damped out. Also,
the various joints increase the variability of the transmission of the vibrations through
the human body.
Additionally, the health risk of vibration training is dependent on the characteristics
of the stimulus itself (Cardinale and Rittweger, 2006). Hand-transmitted vibrations
can cause the so called hand-arm-vibration syndrome experienced by workers using
vibration equipment such as jackhammers whereas long exposure to whole body
vibration in an industrial setting can cause lower back pain (Cardinale and Pope,
2 Background
24
2003). Lower back pain is a very good example of the importance for the right dose
of vibration training as it can be beneficial for the prevention of lower back pain if the
training occurs in small doses.
Figure 2.3: Resonance frequencies of different tissues of the human body (Mester et al.,
2001).
It is noted that there is no ‘recipe’ for the right dose of vibration in order to be
beneficial. As Cardinale et al. (2006) pointed out, the frequently used protocol of 10
minutes vibration training at 2 mm amplitude is above the limits of vibration
exposure for workers in the European Union (The European Parliament and the
Council of the European Union, 2002). However, it may be beneficial in regimented
training. Also other protocols that are reasonable in vibration training are well above
the “caution zones” (Figure 2.4) defined for workers (ISO 2631-1, 1997).
2 Background
25
Figure 2.4: “Caution zones” as defined in the ISO 2631-1 (ISO 2631-1, 1997) compared with
the vibration exposure in previously used vibration training protocol.
When using vibration training, one has to keep in mind the danger of the chosen
method. Each participant will show a different response to this type of training; thus
training protocols should be designed individually. Also, the body should be given
the opportunity to damp the occurring vibration. Consequently, participants, for
example, should never extend their legs fully nor should they sit on the platform as
this limits the ability of the body to respond to the vibration stimulus.
2 Background
2.5
26
General Hypotheses
In summary, research publications have shown in the past decade that vibration
training has become a very popular complement in exercise programs and positive
effects on various musculo-skeletal-systems have been reported. Vibration training
mainly addresses increases in muscle performance and bone mass as well as an
enhanced ability to stabilize body position.
Joining the potential of vibration training and the atrophic processes in humans
observed during a sojourn in microgravity, there seems to be a potential
countermeasure. However, to date, the literature in the field of vibration training is
still very controversial and there seems to be a lack of systematic research which
had been proposed by other previous authors (Cardinale and Wakeling, 2005;
Jordan et al., 2005; Nordlund and Thorstensson, 2007). There is a wide range of
vibration training protocols being used and also a wide range of experiments that
have been applied either during or after the application of vibration training.
Infrequently a whole set of measures has been applied to the same population of
subjects and even less frequently, different tissues have been investigated in the
same study campaign.
Consequently, the general purpose of the Vibration-Bed-Rest-Study (VBR-Study)
was to investigate the effects of 14-days of a 6°-head down tilt bed rest (HDT bed
rest) on the human body in an integrative approach, including skeletal muscle, bone,
knee cartilage, hemodynamics, balance performance and the cardiovascular
system, and to determine whether vibration training can counteract the effects of
immobilization on these systems.
The general hypotheses were:
a) 14-days of HDT bed rest lead to a general deconditioning of the human
body.
b) Vibration training has the potential to counteract deconditioning during
14-days of HDT bed rest in terms of slowing down or preventing the
effects on the human body.
To test these hypotheses, a total of 10 experiments have been conducted during the
VBR-Study, each consisting of multiple measurements. Additionally, blood, urine
and feces samples were taken on all days, as indicated in Table 2.1, in order to
analyze markers of bone and cartilage metabolism, calcium excretion and
2 Background
27
endocrinology of muscle metabolism, cardio-vascular function and hemodynamics.
When establishing the study schedule, a crossover design was chosen and it was
ensured that the different experiments did not impact each other. The order of the
experiments was identical for the two phases of the study.
In this thesis the results of the following experiments will be presented and
discussed:
o
Skeletal Muscle Performance (Chapter 4)
o
Balance Performance (Chapter 5)
o
Cartilage Biology and Morphology (Chapter 6)
2 Background
28
Table 2.1: Overview of the experiments conducted in the VBR-Study. Abbreviations: MRI =
‘Magnet Resonance Imaging’, MRS = ‘Magnet Resonance Spectroscopy’. Subjects
experienced HDT bed rest during the intervention period.
3 General Methods
29
3 General Methods
3.1
Study Design
The Vibration-Bed-Rest-Study (VBR Study) was carried out in August / September
2004 and February / March 2005 in a randomized cross-over-design. Subjects
performed two study phases: one containing the control intervention, the other
containing the vibration training intervention. Each of the two study phases
consisted of 23 days during which the subjects remained stationary in the clinical
research center of the Institute of Aerospace Medicine in the German Aerospace
Center (DLR), in Cologne, Germany. Each study phase was divided into three
periods: a 4-day adaptation period, a 14-day intervention period with bed rest in a
6°-head down tilt (HDT) and a 5-day recovery period (see Table 3.1).
Table 3.1: Study design of the VBR-Study. HDT is the abbreviation for Head-Down-Tilt
(HDT).
Study Phase
Adaptation
normal
A
physical activity
(4 days)
normal
B
physical activity
(4 days)
Intervention
6°-HDT bed rest +
vibration training
(14 days)
6°-HDT bed rest +
control
(14 days)
Recovery
normal
physical activity
(5 days)
normal
physical activity
(5 days)
Both study phases were identical with respect to environmental conditions, study
protocol and diet. How these measures were standardized will be described later in
this chapter.
The subjects were randomly divided into two groups. All subjects completed both
study phases and the order of the study phases was randomized. Subjects were
allowed to walk around inside the clinical research center during the adaptation
period and the recovery period; however, physical exercise was not allowed.
3 General Methods
30
During the intervention periods, subjects were kept in bed for 24h every day at a 6°head down tilt bed rest (HDT bed rest) and were not allowed to elevate their upper
body. All activities, including eating, showering, and weighing, were carried out in
the 6°-HDT position. In the clinical research center, controlled daylight exposure,
constant room temperature and relative humidity were ensured. During the
intervention period, subjects either received vibration training or the control
intervention.
3 General Methods
3.2
31
Study Location
The clinical research center is located in the basement of the building of the Institute
of Aerospace Medicine, DLR, Cologne, Germany. It contains 8 single rooms for the
subject accommodation and two bathrooms in the sleeping area and kitchen, living
room, bathroom and 4 rooms for experiments or storage in the living area.
Figure 3.1: Floor plan for the clinical research centre at the DLR-Institute of Aerospace
Medicine, Cologne, Germany.
3.3
Population
3.3.1 Recruitment Process
For subject recruitment, several media were used for advertisement in order to get a
high number of applicants.
Criteria for subject selection included:
-
a healthy male,
-
age between 18 and 35 years,
-
bodyweight: 75 ± 10 kg,
-
height: 180 ± 10 cm,
-
willingness to participate in
the complete study, including both study
phases,
-
ability to pass a screening test for sinistrin-hypersensitivity.
Criteria for exclusion of the study:
-
regular physical training (more than 3 x per week),
3 General Methods
-
32
drug, alcohol and substance abuse (e.g. regular consumption of more
than 20 – 30 g alcohol / day),
-
adiposity / underweight,
-
smoking,
-
increased risk of thrombosis.
Using a telephone screening questionnaire, the first selection, following the
established criteria, was conducted. Potential subjects then received a detailed
subject information brochure and were invited to an information seminar presented
by the head medical doctor and the study coordinator.
If the applicants remained interested in performing the VBR-study, they were asked
to complete a psychological screening questionnaire. Due to the high demands of
the study protocol for the subjects, these tests were highly relevant as they gave
information about the personality of the candidates and whether they were aware of
and understood their responsibilities if they participated in the study and had the
potential to ‘work’ in a team. The psychological questionnaires were administered
and evaluated by the aviation and space psychologists of the DLR-Institute of
Aerospace Medicine in Hamburg, Germany.
The final selection of the subjects was done using the following criteria:
a) the results of a medical screening at the Aeromedical Center of the DLRInstitute of Aerospace Medicine in Cologne, Germany, which was done by an
independent physician,
b) the content of the individual psychological interviews which were performed
by the aviation and space psychologists of the DLR-Institute of Aerospace
Medicine, the study coordinator and the head physician of the study.
This highly complex screening process was necessary to minimize the risk of
subjects for droping out of the study. Since the study is very complex, a drop out
could not have been replaced and had jeopardized the statistical analysis.
3.3.2 Subjects
Eight healthy male subjects (average ± 1 standard deviation; age: 26 ± 5 years;
mass: 78 ± 10 kg; height: 179 ± 10 cm) participated in this study after giving their
informed consent in accordance with the approval of the Ethics Committee of the
Ärztekammer Nordrhein, Düsseldorf, Germany. All subjects were moderately
physically active, meaning they did not exercise more then three times a week on a
3 General Methods
33
regular basis. None of the subjects were involved in weight lifting or any other
similar recreational sport.
3.4
Vibration Training Intervention
3.4.1 Vibration Training Devise
During the VBR-Study, the Galileo 900 (Novotec Medical GmbH, Pfortzheim,
Germany) was used as the training device (Figure 3.2).
Figure 3.2: The ‘Galileo 900’ vibration platform
The technical data of the platform are the following:
Dimensions:
Height 190 mm / Ø 700 mm
Height with rail:
ca. 1250 mm
Weight:
50 kg
Amplitude:
0 – 5.3 mm (peak – peak)
Frequency range:
5 – 30 Hz
The Galileo vibration platform produces a sinusoidal signal. Differently than all other
plates on the market, the platform produces reciprocating vertical displacements of
the left and right side of a fulcrum like a compensator (Figure 3.3).
3 General Methods
34
Figure 3.3: Mode of operation of the Galileo 900 Vibration platform.
3.4.2 Vibration Training Protocol
The vibration training was applied twice daily in the bed rest period when subjects
received the training intervention. Training sessions were scheduled at least 30
minutes after breakfast and lunch.
Subjects walked a defined path to the training room. The distance was recorded with
an accelerometer-based activity monitor (AMP331; Dynastream Innovations Inc.,
Cochrane, Canada). Each vibration training unit included 5 times of 60 seconds of
isometric exercise units on the vibration platform in an upright standing position with
a knee flexion angle of 30°. The vibration platform vibrated with a frequency of 20
Hz and with about 3 mm amplitude at the centre of the foot. Subjects carried an
additional weight of 15 % of their bodyweight which was adjusted to a diving belt.
Other studies like the ‘Berlin Bed Rest Study’ have used the so called ‘space galileo’
(Bleeker et al., 2005; Blottner et al., 2006; Mulder et al., 2007), which is designed for
training application in the supine position. In our VBR-Study, the subjects trained in
the upright position, although confined to bed rest which was done deliberately.
From the researcher’s perspective we felt that the training intensity could be
controlled more accurately in that position. With training in an upright position,
subjects had to carry their body weight and the load could be increased with free
weights. Also, by defining joint angles and the position of the body on the plate, the
transmission of the vibration could be better controlled and reproduced which meant
standardization of the training was easier to achieve and the scope for the individual
subjects to perform the training differently was smaller. The joint angle was
controlled at the beginning of each exercise with a metal angle. A goniometer was
attached to the knee joint in order to have a visual control of the knee joint
movement.
Between exercise units subjects rested for 60 seconds while sitting on a chair.
3 General Methods
35
During the control intervention, everything, except for the vibration of the plate, was
completely identical with the intervention phase (e.g. schedule, additional load,
standing-sitting-rhythm). The control intervention was designed for the purpose of
investigating the difference in the response between the bed rest with vibration
training and the bed rest without vibration. Consequently, the treatments were
identical except for the application of vibration. We were then able to interpret the
real ‘vibration effect’.
Figure 3.4: Position during the training intervention in the VBR-study.
3 General Methods
3.5
36
Diet
3.5.1 Meal Schedule
Beginning with the adaptation period subjects received a controlled diet throughout
the entire study phase. They ate 3 main meals per day and 3 snacks per day at
predefined times (Table 3.2). Additionally the fluid supply was constant and
controlled.
Table 3.2: Meal schedule for the VBR-Study
Time
08:00
10:30
13:00
16:00
19:00
21:30
22:30
Meal
Breakfast
Snack 1
Lunch
Snack 2
Dinner
Snack 3
Drink
Subjects were asked to consume their meals completely at a specific time. If the
meals could not be served at that time due to experiments, they ate them earlier or
later, depending on the requirements of the experiments. Occasionally, snack, lunch
or dinners were given at the same time. The food menu and the meal frequency
were identical for each subject in both study phases to avoid any impact of nutrients
other than the controlled foods.
3.6.1 Nutrient Intake
The diet of the test subjects was individually tailored according to their body weight.
Energy expenditure was calculated by summing up the resting metabolic rate (RMR)
according to the WHO-equation (DGE et al., 2000), plus 10% of RMR for energy
expenditure because of thermogenesis from food and beverages, plus 40% of RMR
for the light physical activity during the adaptation phase (corresponds to a
PAL (physical activity level)-value of 1.4) and the recovery phase or 10% of RMR
during the 6°-HDT-phase. Dietary protein, fat and carbohydrate intakes were
calculated according to dietary reference intake values (DRI, Ref) (protein: 1g / kg
BW; fat: < 30% of total energy expenditure (TEE); carbohydrate: 55 – 60% TEE).
The relation of vitamins and minerals also matched the DRI; the diet consisted of
200 mmol Sodium (Na+)/day and 1000-1150 mg Ca/day. Subject were given 50 ml
water * kg BW
-1
. All food items varying in sodium content, like bread, cakes or
pastries were homemade. Predefinition of the daily menus for each subject was
done using ‘PRODI’-software (PRODI Version 4.5 LE 2001, Nutri-Science GmbH,
3 General Methods
37
Karlsruhe). Subjects received the exact amount of the food that was predetermined
and this was done by weighing the ingredients, the food items, and the beverages
for each subject on a laboratory scale with a precision of 0.1 mg.
3.6
Environmental Conditions
The clinical research center was completely air conditioned thus it was easy to
control and standardize the environmental conditions independently from the time of
the year when the study period was performed. The control of the environmental
conditions was important in order to avoid sweating or freezing which may affect
energy expenditure. Room temperature and humidity were recorded three times a
day at 8:00 am 16:00 pm and 24:00 pm. The mean values were 23.0 ± 0.9 °C for
temperature and 54.0 ± 5.7 % for humidity.
3.7
Physiotherapy
Subjects received physiotherapy every second to third day during the bed rest
period. Some subjects suffered back pain from lying in bed and a light massage
minimized the pain and also to prevented it. All subjects were treated in the same
way for both study phases and the treatment consisted mainly of a light massage.
Consequently, we do not expect that this treatment affected our results.
3.8
General Statistics
When measurements are taken and recorded, statistical analysis is needed in order
to organize, present and treat the data so that interpretation may occur (Vincent,
2005). Statistical analysis can be distinguished between descriptive and inferential
statistics. Descriptive statistics, which simply describe the conditions and results of
measurements, will be used in this doctoral thesis to analyze the results of the
measurements (e.g., by giving the means and standard deviations of the
measurements and to describe the properties of the subjects, the environmental
conditions, and other variables).
The comparison among population means that are based on samples from the
population will be done by using inferential statistics (Vincent, 2005). One
assumption using inferential statistics is that the mean of a sample of a population
gives an estimate of the mean of the whole population. A prerequisite for this
assumption is that the sample has to be randomly selected. However, using
inferential statistics, one can never be 100% sure about the correctness of the
3 General Methods
38
judgment or estimate one has made. It is always a statement made with a certain
level of confidence. For example, if we claim that there is a difference between two
population means with 90% or 95% confidence, the corresponding values of p would
be 0.10 or 0.05 respectively. Another example is the estimate of a population mean
based on a sample of the population. In this case, the standard deviation or
standard error of a mean indicates the size of the error that may occur when using a
sample mean. Sometimes, a 95% confidence range may be used.
The accuracy of the estimate of the population mean based on a sample depends
on the sample size and the precision of the experimental methods. With decreasing
sample size the risks of a biased sample mean increases.
When performing statistical analysis, there is always the risk of mistakenly rejecting
or accepting the Null-Hypothesis, which is referred to as making type I and type II
errors respectively. In order to create a balance between the risks of making type I
and II errors, the p-value should be chosen carefully. Critical to the decision of the pvalue is the consequence of making each type of error. The decision should always
protect against the most costly error (Vincent, 2005). The only way to reduce the
risks of making the two types of errors simultaneously is to increase the sample
size. The used cross-over-design used in this study has two advantages: (a) the
same group of subjects participated in the measurements under different conditions.
Thus, the differences in the results would be only caused by different experimental
conditions rather than by different groups of subjects and (b) for the given limited
number of subjects, this is a way to make the sample size not too small.
Statistical analysis for all experiments in this doctoral thesis was performed using
the software “Statistica 7.0” from Statsoft (Tulsa, USA). Depending on the type of
measurements, either Student t-Tests or Analysis of Variance (ANOVA) has been
used for statistical analysis. For more details on the specific statistics, see the
method sections in the respective chapters (4 – 6).
Dependent t-tests were used for the experiments where only pre- and post-bed rest
measurements were performed (e.g. balance, cartilage thickness). With the
Student’s t-test, it can be judged whether the means of two populations are different
based on the means, standard deviations and the sizes of the samples from the
populations. There were the following assumptions:
o
the population was normally distributed,
o
the samples were randomly selected from the population,
o
the data were parametric.
3 General Methods
39
For experiments with multiple measurements of the same group of subjects
repeated measures ANOVA was used. One of the assumptions for repeated
measures ANOVA is the homogeneity of variance and the homogeneity of
covariance, collectively referred to as sphericity (Vincent, 2005). The probability of
making a type I error increases when the assumption of sphericity is not met.
Greenhouse Geiser and Huyah-Feldt adjustments were used in this thesis in order
to correct for a violation of the assumption of sphericity.
A Post Hoc test was performed by using the Tukey’s test.
4 Muscle Performance
4
4.1
40
Muscle Performance
Specific Background
The status of muscle mass as well as muscle performance of an individual depends
on the individual activity level. It can only be maintained through usage. Disuse
consequently leads to atrophic processes of muscle. Prolonged disuse of muscles
can occur either due to bed rest after injury and illness or in situations of prolonged
unloading as in space travel. Compared to gravity conditions, where we walk and
move using our legs at least half of the day, in space, the leg muscles are used
infrequently. In space flight, the possibility of long term missions (e.g., a space trip to
Mars) and the lack of appropriate training methods accentuates the need to develop
new training methods in order to prevent atrophy of skeletal muscle. The decreased
muscle performance leads to health problems as soon as astronauts return to a
gravity environment. Resulting training methods of space studies could also be
applied to patients or elderly people with an inactive lifestyle.
4.1.1 Immobilization / Spaceflight
The lack of gravity, compared to a gravity environment, during space travel leads to
a mechanical unloading of the lower extremity. Several studies reported changes in
muscle performance, muscle architecture and muscle biology due to space flight.
Generally, long term exposure to microgravity (e.g., the Skylab missions), causes
decreased muscle performance and muscle size (Thorton and Rummel, 1977). Most
of all, anti-gravity muscles that are responsible for locomotion and postural control,
are affected by microgravity (Aubert et al., 2005). For human skeletal muscle, data
suggested that leg extensors atrophy faster than flexor muscles and showed also an
earlier loss in peak force (Greenleaf et al., 1989). The same authors suggested, that
the longer the missions are, the more similar are the responses of different muscle
groups (Greenleaf et al., 1989). Other authors reported a decline of maximal
voluntary contraction for the calf plantar flexors of up to 48% after a 6 month period
on the space station MIR (Zange et al., 1997) and an average decline of 17% after
90 -180 days in microgravity (Lambertz et al., 2001). It has been suggested (Fitts et
al., 2001), that the observed decreases in peak force may be due to muscle atrophy
and the selective loss of muscle protein (Fitts et al., 2000; Fitts et al., 2001).
Spaceflight also seems to have caused a greater atrophy in the soleus than in the
gastrocnemius fibres (Fitts et al., 2001). Fitts et al. (Fitts et al., 2001) stated that this
41
may be caused by a shift in the neuronal recruitment, favouring the soleus over the
gastrocnemius muscle within the calf. Another reason, that has been suggested is
that muscle with larger fibre diameter during pre-flight showed greater atrophy than
muscles with smaller fibre diameter (Edgerton et al., 1995; Fitts et al., 2001; Widrick
et al., 1999). Although there are no space mission data on muscle protein content,
Fitts et al. (Fitts et al., 2001) suggested the previously shown loss of force per crosssectional area in the slow type 1 fibres (Widrick et al., 1999) may indicate a selective
loss of slow myosin in humans.
In animals, it could be shown, that a 12.5-day space flight led to a significant decline
in myofibril content of the slow-twitch vastus intermedius but not in the fast-twitch
vastus lateralis fibres (Baldwin et al., 1990). Animal studies also showed that within
1 week of exposure to microgravity, muscle mass in rats decreased up to 37% (Fitts
et al., 2000). Additionally, muscles with mainly slow-twitch fibres in rats atrophied
more than fast muscles and the reduction in muscle mass was more pronounced in
the leg extensors, than in the flexors (Jiang et al., 1992; Ohira et al., 1992; Tischler
et al., 1993).
However, data on humans showed a high variability of the observed changes
between individual astronauts and to date, it is not known whether the high
variability was caused by different in-flight countermeasure treatments or was a true
difference in the sensibility of skeletal muscle to microgravity (Fitts et al., 2000; Fitts
et al., 2001; Lambertz et al., 2001; Zange et al., 1997). It is acknowledged that data
collected during space flight are rare and the level of control in terms of pre-flight
training level, in-flight training intensity and nutrition are limited. Also, astronaut’s
motivation to exercise during a mission as well as the opportunities for work out,
vary between missions. To overcome these limitations of in-flight data, models have
been developed that can simulate some of the effects of microgravity on the human
body and also establish an environment that allows for more controlled conditions
compared to space flight. Bed rest at 6°-head-down-tilt limits the weight bearing
activity on all postural body structures and tissues (Adams et al., 2003) and leads to
a fluid shift towards the upper body. Thus, this model can simulate the effects of
microgravity on skeletal muscle structure and function (Kakurin et al., 1976) and
data from a ground based model can be used to support findings that have been
collected from in-flight data. Also, using the bed rest model, it is possible to transfer
the results from such studies to other situation where disuse decreases muscle
mass and muscle performance, such as aging or illness. Additionally, in bed rest
studies, investigators are able to control nutrition and exercise during the study and
42
it is possible to measure a true control group. Adams et al. (Adams et al., 2003)
compared muscle performance data from several different space flights and bed rest
studies and found that generally, bed rest data and in-fight data over the same time
frame show similar results in loss of muscle performance. However, it has to be
taken into account that in-flight data usually represented the effect of microgravity
plus a certain amount of training as a countermeasure whereas bed rest data
included no countermeasure. Consequently, they concluded that the decreases
would even be greater in space fight than in bed rest studies (Adams et al., 2003).
Results from bed rest studies also suggested, that most of the muscle atrophy of the
lower extremity muscles occurred in the first 2-3 weeks after unloading and it
seemed that the rate of loss decreases (Adams et al., 2003) with increasing time in
bed rest.
4.1.2 Countermeasures
Several countermeasures have been developed since humans have travelled into
space. To date, the suggested amount of training for astronauts is 2.5 hour / per
day. The ISS is equipped with a treadmill, a cycle ergometer, electrostimulation
devices and a strength training device. So far, the astronauts are not compelled to
train and their training duration depends on the motivation and also the amount of
free time they have, depending on their working schedule. Thus, training times vary
a lot between astronauts and most of them perform less than 2 hours of training per
day and sustain substantial losses in muscle mass. Although some astronauts
voluntarily perform a high training volume, they still remain susceptible to the
negative effects of spaceflight on the musculoskeletal system.
4.1.3 Vibration Training
Attempting to increase the efficiency of strength training that may affect all tissues of
the musculoskeletal system, in the past decade, vibration training became very
popular as a complement to regular strength training (Jordan et al., 2005). An
increasing number of studies have been published every year. The results have also
been published in various reviews (Cardinale and Wakeling, 2005; Issurin, 2005;
Jordan et al., 2005; Luo et al., 2005; Mester et al., 1999a; Mester et al., 2006;
Nordlund and Thorstensson, 2006; Rehn et al., 2007).
During whole body vibration training, the subject performs isometric or dynamic
exercises on a vibrating platform. Currently, there are two major types of vibration
43
plates. One type of plates produces an oscillating sinusoidal signal where the whole
plate moves uniformly up and down. The other model of vibration plates produces
reciprocating vertical displacements of the left and right side, similar to a
compensator. In addition to the regular parameters such as intensity, repetitions and
amount of series of a specific exercise, training protocols for vibration training can
be adjusted in frequency, amplitude and magnitude. For safety reasons, it has been
suggested to exercise only on the vibration plate with flexed knees, as this position
minimizes the transmission of vibrations to the head (Cardinale and Rittweger,
2006). Various vibration frequencies between 15 Hz and 90 Hz have been used to
either achieve adaptations in skeletal muscle or bone (Issurin, 2005; Rubin et al.,
2002a). The results of the studies investigating the acute effects of vibration training
have been controversial thus far.
Torvinen et al. showed increasing jump height and isometric knee force (Torvinen et
al., 2002a) after 4 minutes of vibration training. Bosco et al. reported increasing
serum levels of testosterone and human growth hormone after 10 sets of 60
seconds of whole body vibration (Bosco et al., 2000b) indicating the augmentation of
anabolic processes. Other studies investigating the acute effects of vibration training
found a decline in muscular performance (De Ruiter et al., 2003; Torvinen et al.,
2002a). Studies on chronic effects of vibration training revealed that over a longer
training cycle, vibration training could be beneficial for muscle performance. Several
studies showed positive training effects on strength and power (Issurin et al., 1994;
Issurin and Tenenbaum, 1999; Liebermann and Issurin, 1997; Mester et al., 1999a).
For example, 21-days of training of a well trained alpine skier lead to a 43%
increase in isometric muscle performance (Mester et al., 1999a).
Increased performance could be the result of an improved synchronization of motor
units and an improved co-contraction of the synergistic muscles (Jordan et al.,
2005). Also, the ‘tonic vibration reflex’ (Hagbarth and Eklund, 1968) has been
described as one of the underlying physiological processes which leads to a reflex
induced muscle contraction that is mainly caused by the stimulation of the muscle
spindles (Burke et al., 1976). On the other hand, vibration inhibits the stretch as well
as the H-reflex (Desmedt and Godaux, 1978). Additionally, it can be assumed that
vibration training also stimulates many other sensory structures in the effected
tissues such as tendons, ligaments, cartilage and bone which consequently may
lead to an adaptation of these structures to the vibration stimulus.
Jordan et al. (Jordan et al., 2005) stated that the variability in outcomes of vibration
studies could be a result of the differences in the training protocols. Most of the
44
protocols used so far, vary in vibration characteristics: position on the plate,
performed exercise on the plate, additional load and others. It is very likely that each
of these parameters affects the physiological response to the applied training.
Therefore, there is a need for well controlled studies to explore the effects of
vibration training.
Vibration training would be applicable in space as it would still be possible to
accelerate a certain mass, in this case a body, although it is weightless. To use
vibration training, it would be necessary to secure the astronaut to the plate with a
belt system, which also is used for in-flight training on the treadmill or the cycle
ergometer.
4.1.4 Purpose of the Study and Hypotheses
As previously discussed, disuse as in bed rest during illness, sedentary lifestyle or
space travel induces a reduction in muscular performance. To date, time efficient
countermeasure programs are still lacking. Several different studies so far
investigated the effects of vibration training on muscle performance; however, there
is a lack of controlled studies. Additionally, the results of vibration training are
controversial. Therefore, the purpose of this study was to investigate the combined
effect of unloading during 14-days of 6°-HDT bed rest and daily vibration training on
maximal voluntary contraction (MVC) and maximal power of the knee flexors and
knee extensors. It was hypothesized, that (a) 14-days of 6°-HDT bed rest without
training would lead to a reduction in MVC and maximal power for the knee flexor
and extensor muscles and that (b) bed rest with vibration training would lead to a
smaller reduction in these parameters or even avoid any losses in muscle
performance.
4.2
45
Specific Methods
4.2.1 Muscle Performance Testing
Strength performance testing was conducted three times throughout each study
phase (Table 4.1) (see also (Schmidt, 2006). The series of measurements started
with a baseline measure at day -1 of the adaptation phase, which was the day
directly prior to bed rest, followed by a re-test at day R1 of the recovery phase after
the subject got up from the bed rest and finished with a last measure at the R5 of
the recovery period. Measurements were performed in the laboratory of the Institute
of Training Science and Sport Informatics at the German Sport University in
Cologne, Germany. All measures of muscle performance were carried out at the
same time of day in the afternoon. At day R1 the measurement was performed
approximately 24h after the last vibration training session and approximately 8h after
subjects left the 6°-HDT position.
Muscle
Performance
Vibration
Training
Table 4.1: Study design of the VBR-Study. Muscle Performance was measured during the
Adaptation and the Recovery period. In the intervention phase subject were immobilized at
5°-HDT-bed rest. During that time period, subjects either engaged in vibration training or the
control intervention.
Regular strength training devices (Gym 80, Gelsenkirchen, Germany) equipped with
a force transducer and a displacement transducer (mechaTronic GmbH, Hamm,
Germany) allowed us to measure isometric and dynamic forces for the knee
extensor and knee flexor muscle groups. Data recording and data analysis was
performed with the commercial software (windigi, DigiMax, mechaTronic GmbH,
Germany, Version 8.1). The two parameters measured were maximal voluntary
contraction and power for the knee flexor and knee extensor muscles.
Prior to the strength test, subjects performed a 5 minute warm up on a treadmill at
2.5 m / s walking speed. Also all subjects had to perform a specific warm up at each
R5
R4
R3
R2
R1
14
13
12
11
Recovery
10
9
8
7
6
5
4
3
2
Intervention
1
-1
-2
-3
Experiment
Day
-4
Adaptation
46
of the training devices consisting of 1 set of 8 repetitions with a load of 5 kg. This
specific warm up was supposed to give the subject the chance to get used to the
device as well as to the movement they were asked to do. All training devices were
adjusted to the individual anthropometric values, meaning that for the dynamic as
well as the isometric measures, joint angles were used to reflect the optimal joint
position for the specific movements (Baratta et al., 1988; Herzog et al., 1991;
Savelberg and Meijer, 2003; Solomonow et al., 1987; Ullrich and Brueggemann,
2007). The goal of controlling the joint angles for each subject individually was to get
as close as possible with the used methods to an optimal muscle length for the
required movement. Settings of the training devices were identical for all repeated
measurements.
4.2.1.1
Isometric Measurements
For isometric maximal voluntary contraction (MVC) measurement the lever arms of
the training devices were adjusted, to reduce, as much as possible, any additional
movement. Joint positions were set at 60° knee flexion and 90° hip flexion for the
knee extensor measurements and 20° knee flexion for the knee flexor
measurements. After the specific warm up, the lever arm was adjusted and the
subjects were asked to perform one test trial followed by three real MVC
measurement. After receiving a previously learned command, they pressed, to the
maximum, against the resistance with both legs at once. Between repetitions,
subjects had a 120 seconds break. No verbal motivation was used throughout the
study to ensure consistent conditions for all six measures of muscle performance.
The highest force out of the three recorded values was included as MVC into the
statistical analysis. Subjects were deprived of their reached maximal strength values
in order to minimize a personal bias.
4.2.1.2
Dynamic Measurements
For the dynamic measurements, the mass that had to be accelerated was adjusted
to the individually determined 50% MVC. Thus, the mass was recalculated for each
of the strength testing sessions throughout the study. When the MVC decreased,
consequently the mass subjects had to accelerate decreased as well. The maximal
power achieved in this measure was included into the statistical analyses.
47
4.2.2 Statistical analyses
Statistical analyses were performed using STATISTICA software (Version 7.0,
StatSoft, Inc., Tulsa, USA). Randomization of subjects was tested using factorial
analyses of variance (ANOVA) prior to all other statistical tests. The time effects of
bed rest and vibration training on MVC and maximal power values were tested using
repeated measures ANOVA. Data for the control intervention and the vibration
training intervention were compared using ANOVA within-within. Significant
differences were adjusted using Greenhouse Geiser correction and Huynh-Feldt
(HF) adjustments. Post hoc tests were performed in order to further analyze time
effects for the different days. Differences were regarded to be statistically significant
at P < 0.05. All results are shown as means ± SD.
4.3
48
Results
Factorial ANOVA revealed no effect of the randomization of subjects to the order of
the treatment. There was no difference in baseline performance levels between the
two groups. Also, it did not affect the results whether subject started with the control
or with the vibration training intervention; hence, there was no learning effect
between the two different study phases. Thus, the subsequent statistical analyses of
the data were divided only into the two intervention groups.
Maximum voluntary contraction (MVC) did not decrease significantly for the knee
flexor and knee extensor muscles when subjects receive bed rest only (Table 4.2
and 4.3).
When subjects received vibration training, there was a significant decrease in MVC
for the knee flexor muscles (p=0.003) but not for the knee extensor muscles.
Maximal power at 50% of the MCV values did not change significantly throughout
the time course of measures for the knee flexor muscles. However, there was a
significant decrease in maximal power of the knee flexors when subjects received
vibration training (p=0.047).
Table 4.2: Effects of HDT bed rest on muscle performance for knee extensors and flexor
muscles.
Vibration training could prevent a decrease of maximal power in the knee extensor
muscles. When subjects received the control intervention, maximal power
decreased significantly (p=0.007), whereas there was no statistical significance in
maximal power when subjects received vibration training. These results were
49
confirmed by an ANOVA within-within, where a significant difference in the effect of
the two treatments was found (p=0.001).
When MVC or maximal power showed a significant reduction in the achieved
values, subjects did not recover to baseline levels after the five day recovery period.
In contrast, the maximal power and MVC of the knee flexors values further
decreased, although subjects were mobile in the laboratory again (see Table 4.3).
Table 4.3: Muscle performance for the knee extensor and knee flexor muscles before and
after HDT bed rest. Following are the results for the control and the vibration intervention.
Asterisks indicate a significant difference (p < 0.05) between baseline and the respective
value.
Intervention
pre-HDT
post-HDT
post-HDT
(day -1)
(day R1)
(day R5)
1287 ± 314
1190 ± 209
1168 ± 219
-5 %
-6 %
1240 ± 213
1188 ± 200*
-4 %
-7 %*
614 ± 134
617 ± 122
-2 %
3%
676 ± 157
608 ± 167*
-7 %
-10 %*
2196 ±445
2131 ± 440
-2 %
-6 %
2076 ± 460
2253 ± 642
-9 %
-2 %
811 ± 237*
871 ± 253
-12 %*
-5 %
825 ± 201
801 ± 250
-12 %
-7 %
Knee flexors
MVC [Newton]
control
% change
vibration
1284 ± 206
% change
Power [Watt]
control
645 ± 196
% change
vibration
699 ± 179
% change
Knee extensors
MVC [Newton]
control
2250 ± 439
% change
vibration
2305 ± 519
% change
Power [Watt]
control
915 ±211
% change
vibration
% change
927 ± 263
4.4
50
Discussion
The purpose of this study was to investigate the combined effect of unloading during
14-days of 6°-HDT bed rest and daily vibration training on MVC and maximal power
of the knee flexors and knee extensors.
The first hypothesis, that 14 days of 6°-HDT bed rest without training would lead to a
reduction in MVC and maximal power for the knee flexor and extensor muscles
could not, in general, be confirmed. MVC did not decrease significantly for leg
extensor and leg flexor muscles after 14 days of strict bed rest. This is surprising as
14 days of bed rest due to illness or 14 days of casting of a joint may have major
effects on muscle performance. Deconditioning, due to injury or illness is often
caused by total joint immobilization, for example, with a cast or caused by neural
inhibition due to pain. Thus, the above conditions of immobilization are not
comparable with the conditions to which our subjects were exposed to as they were
allowed to move their joints as long as they did not leave the 6°-HDT-position.
Additionally, they walked a defined path to the training room twice every day which
did not affect the known effects of bed rest on the cardio-vascular system
(unpublished data); however, it may have affected the impact of 14 days of bed rest
on muscular performance.
Pre-bed rest muscle and training status seem also to have a major impact on the
deconditioning of muscle during bed rest. The subjects in our study were untrained.
Thus, the activity level during bed rest plus walking some meters every day may not
have been much different from their daily activity outside the lab. If this was the
case, for our subjects bed rest, as the initial stimulus for detraining, may not have
been effective. Wackerhage et al. (2006) (Wackerhage H. and Atherton P., 2006)
hypothesized that there is a ‘moving threshold’ for the intensity that is necessary to
initiate muscle growth. This would mean that an atrophied muscle needs less
stimulation to start anabolic processes than a hypertrophied muscle. Other authors
(Phillips et al., 1999) showed that in untrained subjects lower levels of resistance
training lead to muscle protein synthesis than in resistance trained athletes.
Possibly, the opposite mechanism holds true for detraining processes. For untrained
subjects, lower levels of activity and longer periods of de-activation may be needed
to initiate catabolic processes in skeletal muscle than in resistance-trained subjects.
It also has to be considered that the energy intake of our subjects was controlled.
This means that they consumed the amount of food required to be in a balanced
51
energy status (DGE et al., 2000). The massive decrease of muscle performance
during space flight and in illness or injury induced bed rest is partly due to
hypocaloric food intake (Biolo et al., 2007). Our results show that if subjects receive
a diet tailored to their energy requirements, they do not necessarily show a
decreased muscle performance. The chosen PAL-value in our study was at a level
for primarily sitting daily activity. The finding that the subjects were in a balanced
energy state with that chosen PAL-value also supports the statement that the
activity level during the study may not have been much different to their daily
activities for some of the them.
Our data show that there is no general response of the lower extremity muscles to
bed rest. The response of skeletal muscle to 14 days of bed rest is muscle specific.
The maximal power decreases earlier and is more pronounced in knee extensor
than in knee flexor muscles. This finding supports the results of previous studies,
which reported earlier and greater losses in extensor muscles (Greenleaf et al.,
1989). They suggested that the longer a space mission lasted, the more similar
were the losses in muscle performance between different muscle groups. Atrophy
may occur earlier and is more pronounced in muscles, for example, anti –gravity
muscles, that are used extensively under gravity conditions (Aubert et al., 2005) as
well as in muscles with larger diameter (Edgerton et al., 1995; Fitts et al., 2001;
Widrick et al., 1999). The knee extensor muscle has one of the largest girths in most
of the people and even in untrained individuals, it is one of the most frequently used
muscles since it maintains the body in an upright position or lifts it against gravity.
There is often a neuromuscular disbalance between the knee extensor and flexor
muscles. Thus the knee flexor muscle may not recognize a 14-day bed rest period
as a major change in the normal pattern of usage and therefore show a latent
response.
Additionally, the length of a muscle in immobilization is critical for the occurring
effects. Although our subjects were not “fixed” in a certain position, they spent their
days lying in bed with their knee joint extended most of the time. This meant a short
muscle length for the knee extensors that would encourage the loss of sarcomeres
from the ends of the fascicles. For the knee flexors, on the other hand, an extended
knee position means that they are at their maximal length. Since the sarcomeres in
series are one important factor for the maximal power of a muscle, the above
mentioned “length theory” may explain the different responses of the two muscle
groups.
52
In summary, the changes in MVC and Power after 14-days of immobilization of
healthy subjects with controlled diet are muscle specific and may depend on the
physical status pre-bed rest.
The second hypothesis was that vibration training will lead to a smaller reduction or
avoids losses in MVC and Power in knee flexor and extensor muscles. Vibration
training lead to less decrease in power for the knee extensors meaning the rate of
change in muscle performance due to bed rest could be decreased with the applied
training protocol. A static squat position at a knee flexion angle of 30° activates the
knee extensors as agonists more than the knee flexors. The superimposed vibration
in this position may induce an eccentric load at the level of muscle fibres that is
more effective for the knee extensors than for the knee flexors. More specific
exercises on the vibration plate may also lead to less decrease in the knee flexor
muscles.
The bed rest intervention did not result in a significant decrease in the MVC values
of our subjects. Thus, the expected decrease in muscle performance that we hoped
to avoid with our training intervention could not be observed. This finding makes it
more difficult to show positive effects of vibration training. With the volume and
intensity of our training program, we did not intend to increase muscle performance.
Taking this into account, it is not surprising that vibration training during bed rest did
not lead to a much different response in MVC values than bed rest alone.
If muscle performance decreased due to bed rest, as the power data for the knee
extensors showed, vibration training could counteract this effect. The power data
also show that although the MVC was the same before and after bed rest, the ability
of the subjects to maximally accelerate a given mass, decreased. The decreased
power could, for example, be caused by a lower intramuscular coordination or a
change in the quality of muscle. Maximal power also depends on the length of the
muscle, hence, the sarcomeres in series. Riley et al. (Riley et al., 2000) reported a
decreased length in some fibres after short periods in space. That this holds true for
the knee extensor again supports the finding that the knee extensors adapt earlier
than the knee flexors.
Only one comparable study has been conducted in recent years. In the ‘Berlin Bed
Rest Study’, 20 male volunteer were immobilized for 56 days in head down tilt bed
rest (Blottner et al., 2006). They received a combination of whole body vibration and
resistance training twice daily for 6 minutes on the ‘Galileo Space’ device at
frequencies between 19 and 25 Hz. The group found that the vibration training
group showed less reduction in maximal voluntary contraction of the plantar flexors.
53
Additionally, they showed an increase in soleus myofibres type I and type II in the
vibration training group and suggested this could be due to hypertrophy.
Unfortunately, a control intervention with “vibration-only” or with “resistive exercise
only” was missing in this study. Consequently, it was not possible to distinguish
between vibration and resistance training effects.
The findings of the ‘Berlin Bed Rest Study’ are not in conflict with the results of this
study as the length of immobilization is much different. It may be that atrophic
processes start later than after 14 days off bed rest if nutrition is controlled and
subjects are not in a cast. However, our results would support the hypothesis that
vibration training may act as a potential countermeasure for bed rest induced
muscle atrophy.
Maximal velocity and power give a different insight into muscle function and possible
adaptations of space flight. Whereas the maximal voluntary contraction (MVC) only
reflects the alterations in strength at one given joint angle, the force-velocity
relationship describes the amount of force that can be produced at any given
shortening velocity. The product of force and velocity is mechanical power, which is
an important functional measure. Maximal force is mostly dependent on the number
of sarcomeres in parallel, whereas Vmax is highly dependent of the sarcomeres in
series. Due to technical limitations, the effect of microgravity on the force- and
power-velocity relationship is inadequately studied (Adams et al., 2003) so far.
The force-velocity relationship of ankle plantar flexor and extensor muscle showed a
reduction after long (110-237 days) as well as short (7 days) term missions
(Grigoriev et al., 1991; Kozlovskaya et al., 1981). More specifically, the decreased
strength in the ankle plantar flexor was greatest at high angular velocities. On the
other hand, Trappe et al. (2001) found no effects of 17-days of space flight in the
torque velocity relationship for the ankle plantar flexors (Trappe et al., 2001).
4.4.1 Limitations of the Design
The vibration bed rest study was designed as a cross over study in order to account
for the small number of subjects. Thus, it was possible to compare the effects for
each subject individually as each of them conducted two interventions, the control
and the training intervention. The training load was tailored to body weight. It may
have been optimal to tailor the training intensity to each subject’s pre-bed rest
training level. However, our subjects were not athletes, meaning they were not
trained. We assumed, therefore, that their muscles’ work load was mainly carrying
54
their body weight. Therefore, normalizing the training load to body weight seems
appropriate. Also, we did not increase the training load progressively, but it was
consistent over the whole 14 days of bed rest. A progressive increasing training load
may have led to more distinct differences between the training and the control
group.
Generally, we chose a relatively low training load. However, as this was the first
study to implement isolated vibration training in a bed rest study and vibration
training is recognized as a very intense training method, the main goal, besides, of
course to prevent deconditioning, was to prevent injury to our subjects. It is
recommended that future studies incorporate a higher training intensity and a
progression of the training load to increase anabolic effects of vibration training.
The upright training position has been chosen consciously. Compared to a lying
position, we felt that training upright would provide more control of what the subjects
actually did during their training. Also, the transmission of the vibration through the
body is identical with the training situation in space and therefore seems more
appropriate.
In summary, during the vibration bed rest study, vibration training during 14-days of
6°-HDT bed rest led to less decrease of power in the knee extensors. Thus, the
used training protocol was sufficient to minimize the decrease for power of the knee
extensors. Surprisingly, bed rest did not lead to a decrease in MVC of knee flexors
and extensors in our subjects. In conclusion changes in MVC and power after 14days of immobilization of healthy subjects with controlled diet are muscle specific
and may depend on the physical status prior to bed rest.
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5 Balance
5.1
Specific Background
The ability to stabilize body position is mandatory for the performance of movement
(Wilke, 2000) and is highly dependent upon the grade of experience. For example,
gymnasts who exercise on the high beam, skateboarders and other individuals who
are regularly exposed to an ‘unstable’ ground, perform much better in balance than
others who do not force the ‘balance system’ as much. During spaceflight, the
demands on the lower extremity muscles are reduced to a minimum which not only
leads to changes in muscle performance but also affects the ability to stabilize body
position. These changes in body control are not of much importance as long as the
astronauts stay in a microgravity environment. However, as soon as they return to a
gravity environment, for instance, to Earth, Moon or Mars, the degenerative effects
can lead to major safety and injury risks (Hrysomallis, 2007). This is important to be
aware of, especially when astronauts in the near future are on interplanetary
missions, where they don’t have the physical support from team members on earth.
As with most of the data obtained in space flight, the sample size is very small and it
is difficult to generalize the results gained during spaceflight and draw conclusions
for a normal population. However, knowledge obtained from spaceflight in that field
is very important as it mimics the absence of load and gravitation on the human
body perfectly. The rare occasion of having an astronaut as a subject led to the
development of models that can simulate the effects of microgravity on the human
body. Immobilization in 6°-head down tilt bed rest (HDT-bed rest) can simulate some
of the effects space flight has on the musculoskeletal system. Recorded results from
spaceflight or immobilization studies may help to better understand the processes
involved in the ability to stabilize body position and even more importantly, to
develop adequate countermeasures.
5.1.1 General Physiology
The ability to “keep balance” is the result of the interaction of many different organic
and reflex systems of the human body.
To be able to coordinate movement and body position, the brain needs useful
information about the position of the body in space. Proprioception is the sense of
the position in space, where the sensory input is collected through sensors entitled
mechano-receptors or proprioceptors. The different receptors can be classified by
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the organs or tissues which they are located in, (e.g., joints, muscles, tendons,
ligaments, the skin and the vestibular organs) and through their function (Table 5.1).
The collected sensory information is then transmitted to the central nervous system
(Shaffer and Harrison, 2007).
Table 5.1: Mechano-receptors in humans
Receptor
Muscle Spindles
Location
skeletal muscle
Function
- sense muscle stretch
- causes agonist contraction and
antagonist relaxation
Pacinian
near joints in the deep
Corpuscle
subcutaneous tissue
Golgi-Receptors
tendons and ligaments
- sense rapid changes in pressure
and vibrations
- low excitation level
- measure tension
- can enhance or inhibit muscle
activity of the whole extremity
- measure skin stretch
Ruffini Endings
joint capsule
Free Nerve
all tissues except cartilage - detect changes in pressure,
Endings
temperature, pain and stretch
The vestibular organ is located in the inner ear and it represents a mechano-sensory
organ. Its role is to stabilize the field of vision and to control the upright body position
(Clarke and Scherer, 2001). There is a strong connection between the vestibular
system and motor activity since the afferent information from the vestibular system
is being used to stabilize eye movement and body position. Ocular counter rolling
represents one example for an otolith-ocular reflex which occurs in response to the
activation of the otholiths which are located in the inner ear (Moore et al., 2001).
Receptors play a major role in reflex-loops as they deliver the afferent input signals.
In postural control, the two important reflex loops are the vestibulo-ocular reflex and
the vestibulo-spinal-reflex. The first enables the body to stabilize the field of vision
as the head moves. Although this reflex loop is affected by a microgravity
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environment, we will not include it here as we will not be able to measure the impact
of bed rest on this system in the experiments performed in this study.
The vestibulo-spinal-reflex is responsible for the regulation of the muscle tone that is
necessary to keep the body in an upright position. To accomplish this, the vestibular
system is connected with the “anti-gravity-neurons” that trigger the muscle spindle
reflexes (Clarke and Scherer, 2001; Scherer, 1997).
5.1.2 Adaptation during Spaceflight and Immobilization
5.1.2.1
Spaceflight
The absence of normal gravitational loading or immobilization as in injury, aging or
disability, leads to changes in the sensibility of the receptors. This can result in the
inability to estimate the position of the body in space correctly (Olivier and Fakler,
2005). In the long term, a complete “set” of input signals is necessary to be able to
control the body’s equilibrium (Dietz and Duysens, 2000). The special conditions in
space are characterized by a relatively low muscle activity that is necessary to keep
the body in a balanced position (Edgerton et al., 2001; Lestienne and Gurfinkel,
1988). Since the sensory input for the lower extremity muscles is missing in
microgravity, it has been shown that peripheral and central neural processes are
physiologically and functionally altered when astronauts return from a stay in
microgravity (Clement et al., 2005).
Also, massive irritation of the control of body position and movement after a stay in
microgravity have been investigated by different authors (Graybiel, 1980; Grigoriev
et al., 1991; Homick and Reschke, 1977; Paloski et al., 1992b; Paloski et al.,
1992a). The explanation seems obvious in that the anti-gravitational muscles
showed the most severe atrophy of all skeletal muscle (e.g. (Edgerton et al., 2001)
and they are the major muscle groups responsible for keeping the body in an upright
position under gravitational conditions (Baroni et al., 2001a).
Additionally, the function of receptors generally changes in a microgravity
environment. Due to the microgravitational environment, all gravitationally
dependent functions of the vestibular system are irritated which leads to “illusory
motions” (Reschke et al., 1994; Reschke et al., 1998) and motion sickness with
symptoms like dizziness and malaise (Mittelstaedt, 1999). The reason for motion
sickness is mainly due to the inability of the otholiths to sense accelerations as their
physiological functionality depends on the presence of gravity (Lackner and Dizio,
2000; Mittelstaedt and Glasauer, 1993). On the other hand, Ross et al. (1993) could
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show in a rat experiment that the morphology of the vestibular organs, such as the
otholiths, did not seem to be affected by microgravity. After 10 – 14 days of
spaceflight, no changes in their morphological development could be determined.
However, neuronal connections between the single sensory cells increased 12-fold
(Ross, 1993) which indicated a high plasticity of the vestibular organs in response to
changes of the environment (Clarke and Scherer, 2001).
Beside motion sickness at the beginning of a flight, the main health issues
associated with the effects of microgravity on balance occur after the return to a
gravitational environment (e.g., earth). The re-adaptation to gravity also causes
dizziness as in “motion sickness” (Clement et al., 2005), which is comparable to the
swinging movement that people experience when they leave a boat after a longer
trip and step on rigid ground again.
Also, the response patterns of the muscle spindles change, as they sense a different
length of the muscle due to the lack of gravity (Baroni et al., 2001b; Dietz et al.,
1989; Matthews, 1981; Matthews, 1988). This results, for example, in the inability to
reproduce a joint angle without visual control (Clement et al., 1984) after a stay in
microgravity.
Due to the negative adaptations of skeletal muscle to microgravity the vestibulospinal-reflexes also decrease which leads to difficulties in controlling an upright body
position as well as the coordination of a uniform gait when astronauts return to earth
(Clarke and Scherer, 2001; Clement and Reschke, 1996). As a result of that, the
decrease of the vestibulo-spinal reflex leads to irritation of the muscle spindles
(Reschke et al., 1984; Watt et al., 1986). In this context Roll et al. (Roll et al., 1993)
stated that the weakening of the vestibulo-spinal reflexes could lead to lower
excitation of the anti-gravity muscles which would explain the reduced ability to
control movement and position during space flight. Roll et al. confirmed their results
with experiments that could show only a limited ability to elicit the H-reflex in
response to the application of vibrations on a tendon after 21 days in microgravity
(Roll et al., 1993). The same experiment led to the conclusion that biomechanical
properties of certain receptors also changed since they showed lower activateability
of the proprioceptors.
Cherepakhin et al. (Cherepakhin et al., 1973) studied the human sensorimotor
coordination after 18 days of spaceflight. The ability to maintain the vertical posture
decreased and it took 10 days after their return from microgravity until values were
at baseline levels again.
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5.1.2.2
59
Immobilization
Decreased mobility usually causes decreased skeletal muscle performance which
plays a major role in the ability to keep balance. For example, the strong synergy
between agonistic and antagonistic muscles is very important for the intra- and
intermuscular coordination and one should expect postural control to worsen with
decreasing muscle performance. Immobilization always reflects a decrease in
dynamic input signals. It is expected that with immobilization due to injury or trauma
an “atrophy in dynamic receptors” can occur (Froböse et al., 2003).
Muscle tonus is a result of the body’s challenge to keep an upright position against
the force of gravity and it will be reduced after prolonged immobilization
(Wiesendanger, 1997). During immobilization, the mechanisms that regulate the
muscle tone receive smaller input signals from receptors, the vestibular system and
the visual system which leads to an adaptation of skeletal muscle to the current
conditions. All these mechanisms would also add to a decrease in coordination.
Changes in the body’s ability to maintain equilibrium may also be caused by muscle
atrophy. If, after atrophic processes, the body is challenged with stability exercises,
the requirements for the muscle increase with the increasing difficulty of the exercise
(Wilke et al., 2003). Thus, a decrease in skeletal muscle performance, due to injury
or immobilization leads to the decreased ability of muscle to support the body in
‘keeping balance’.
Davis et al. (Davis et al., 1997) investigated the effects of head down tilt bed rest on
postural control. EMG measurement before and after 5 days of bed rest showed that
immobilization increases muscle activity of the lower extremity during walking which
corresponds to a decreased ability of postural control. Exercise interventions during
the bed rest intervention could not counteract this effect. The group limits their
results to the finding that the used protocol may not have been sufficient to
counteract the bed rest effect. It is also noted that longitudinal electromyographic
studies face specific problems in the standardization and calibration of the signals.
Different studies showed a reduction of electromyographic activity during
immobilization (Alkner and Tesch, 2004) as well as a change in conduction velocity
(Rüegg et al., 1998). The conduction velocity decreased due to a smaller muscle
cross sectional area and a recovery to normal values needed approximately 14 days
of normal mobilization.
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The application of vibrations to the human body activates the neuro-muscular
system (Haas et al., 2004) and consequently, should also effect the coordination of
movement. As previously described, many studies investigated the effect of
vibration training on performance parameters as maximal force or power (see
chapter 2.3.4.2) and although the results are controversial it seems more likely that
vibration training does have the potential to elicit anabolic processes. If this method
is able to enhance muscle performance, there should also be an effect on the
coordinative portion of movement. Also, if one studies the properties of mechanical
receptors, it becomes clear that they are sensitive for the properties of a vibratory
input signal, especially the Pacinian corpuscle.
Studies on the effects of vibration training or vibration stimuli on balance and
coordinative processes have mostly been performed in medical environments, for
example in the context of rehabilitation of orthopedic injuries or in the prevention of
risks in falling for elderly people (Ahlborg et al., 2006; Bautmans et al., 2005;
Bogaerts et al., 2006; Brunetti et al., 2006; Bruyere et al., 2005; Gusi et al., 2006;
Kawanabe et al., 2007; Torvinen et al., 2002a; Torvinen et al., 2002b; Torvinen et
al., 2003).
Berschin et al. (Berschin and Sommer, 2004) observed an increased co-activation of
synergistic muscle groups in response to vibration training which is necessary for
joint stability. Therefore, they suggested to using this training method as a tool in the
rehabilitation of anterior cruciate ligament (ACL) deficient patients as well as for the
prevention of injuries in people with predisposed joint instability. Also, they stated
that vibration training may stimulate receptors that have been affected through the
injury as well.
Vibration training can influence movement control in terms of an incorrect estimation
of joint angles (Cordo et al., 1995). The irritation of the proprioception is thereby
dependent on the vibration frequency (Kasai et al., 1992), the velocity of movement
(Steyvers et al., 2001) and the activation level of the muscle (Haas et al., 2004).
Furthermore, vibration can lead to body tilting if calf muscles are stimulated during
quiet standing (Eklund, 1972) or to movement illusions if the trunk is fixed and thus
unable to move (Lackner and Levine, 1979). These effects are dependent upon the
stability of the supporting surface upon which the subjects stand. They are
attenuated if the subjects stand on an unstable surface (Ivanenko et al., 1999).
Experiments during walking showed that vibration of the thigh muscles altered the
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walking speed depending on the direction of the progression (Ivanenko et al., 2000).
Ivanenko at el. (2000) concluded that the proprioceptive input from the muscle
spindles is important for the maintenance of a steady state during human
locomotion. The proprioceptive influence of the muscle spindles is task specific and
it seems that the information about the movement of the foot relative to the trunk is
important for the control of the walking speed.
Vibration training is being successfully applied for the prevention of risks in falling
among elderly people. Bruyere et al. (2005) reported an improvement of health
related quality of life in nursing home residents. They improved their walking ability
and minimized the risk of falling after 6 weeks of whole body vibration compared to
the control group (Bruyere et al., 2005). A different group confirmed these findings
with improved performance of timed up-and go and the Tinetti-test after 6 weeks of
vibration training with nursing home residents (Bautmans et al., 2005). Kawanabe et
al. (2007) only recently investigated the effect of a 2 month vibration training
program added to an exercise routine compared to the exercise routine only for
elderly people. Although subjects trained only once a week, they improved walking
speed, stride length and standing time on one leg compared to the control group
(Kawanabe et al., 2007).
Vibration training becomes also popular as a training method in the treatment of
neurological diseases and injuries such as Parkinson Disease (Novak and Novak,
2006; Turbanski et al., 2005), Multiple Sclerosis (Schuhfried et al., 2005) and
paraplegic patients (Melchiorri et al., 2007).
Postural control of patients with Parkinson Disease, for instance, could be enhanced
spontaneously with a treatment of 5 x 60sec of vibration at 6Hz (Turbanski et al.,
2005). Postural stability was enhanced after the training and Turbanski et al. (2005)
stated that it may serve as an alternate treatment method that could potentially
enable the patients with Parkinson Disease to adopt a more active way of life.
In summary, the observations of the effects of spaceflight on balance previously
described, show, that a decrease in balance ability can become a major health risk
in space flight since it can lead to injuries. The development of good training
programs that avoid these effects is very important and can also have an impact on
the design of rehabilitation or prevention programs for elderly people who also show
an increase in risks of falling and consequently are at higher risk for bone injuries.
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The effects of head down tilt bed rest on balance performance under controlled
conditions remain unknown. Vibration training seems to be a promising complement
to regular strength training and additionally may have an impact on balance
performance, as previously described.
Therefore, the purpose of our study was to investigate the effects of 14-days headdown-tilt bed rest on balance performance as measured with the Posturomed®
device and to test the impact of a vibration training protocol on the effects of bed
rest. The hypotheses were the following:
a) 14-days of head down tilt bed rest negatively affects the ability to stabilize
body position as measured with the Posturomed® device; and
b) Vibration training during 14-days of head down tilt bed rest can minimize the
negative effects of immobilization on balance performance.
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5.2
63
Methods
5.2.1 Posturomed® Device
In this study, ‘balance’ is defined as the ability to stabilize body position. Following,
both of the terms ‘balance performance’ and ‘balance ability’ will be used in
reference to the ability to stabilize body position.
For the balance experiment, the Posturomed® device (Haider Bioswing, Euskirchen)
was used (Figure 5.1). The device is built out of three main elements that are
mounted on top of each other: a platform, an intermediate plate and a ground plate.
The platform is the top layer and is coated with a plastic material to avoid slipping. It
is 60 cm X 60 cm and can swing in two directions, anterior-posterior and mediallateral. For safety reasons, the platform is surrounded by a handrail on three sides
which gives the subjects or patients something to hold on to.
Figure 5.1: The Posturomed® device used in the study
The platform is attached to 4 special ‘Bioswing’-swing devices that allow for
movement in two independent swing circles. The amplitude of the platform can be
adjusted with the help of two brakes that are attached to the side of the
Posturomed®. This results in three levels of difficulty: free swing in two directions,
free swing in one direction and constricted swinging in both directions (Rasev and
Haider, 1995).
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The Posturomed® used in the study was equipped with an accelerometer at one
side of the platform that could sense accelerations of the plate in the horizontal
plane in the two described directions (see Figure 5.2). Additionally, sensors were
attached to the platform that recorded changes in the path-time course of the plate.
The data were recorded at 500 Hz sampling frequency, then transferred through an
amplifier to an analogue / digital transducer and finally processed with special
software in the associated computer.
Afterwards, a mechaTronic software enables the user to display the movement of
the platform on the screen. All technical data and technical details are also
described by Rasev and Haider (1995).
Figure 5.2: Position-time diagram of the Posturomed®.
Using the Posturomed® device, ‘balance’ is described in the displacement of the
platform in mm in the two different directions. A good ability to balance the body is
defined through a small displacement of the platform in either direction, whereas big
displacements are considered to reflect a bad ability to stabilize the body position
(Schlumberger and Schmidtbleicher, 1998).
An additional feature to measure balance ability is a displacement mechanism
(Müller et al., 2004). It enables the researcher to assess the reactive ability to
stabilize the body. Subsequently, this test will be named ‘provocation’. The platform
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is dislocated and adjusted in the medial-lateral direction by 20 mm. When eliciting
the fixation, the platform follows gravity and swings sideways. The subject is asked
to re-stabilize as fast as possible again.
The Posturomed® device has been used in the diagnosis of balance and also in the
training of sensori-mortor and neuro-muscular abilities (Wilke et al., 2003).
5.2.2 Test Protocol
The balance test was performed on study-days -4 and R1. In the morning of day -4
an extra session was performed in order to familiarize with the experiment. The goal
was to minimize the learning effects as much as possible in order to prevent the
results from being biased by such an effect. Therefore, the subjects were introduced
to the Posturomed® device and the different tasks they had to perform. This is very
important, especially for the subjects with lower balance ability. These trials were
also recorded in order to compare, if necessary, the values with the second pre-bed
rest session. The actual data collection was done in the afternoon of day -4. The
results of the pre-bed rest measure were considered the ‘normal’ values and postbed rest values were related to these values.
The post-bed rest measurement was conducted on day R1, immediately after
subjects finalized the immobilization period with the tilt-table-experiment. All subjects
walked a distance of about 15m from the tilt table experiment to the testing room for
the balance experiment. Procedures were identical for the control and the vibration
condition.
The whole balance experiment consisted of 6 different tasks that increased in their
degree of difficulty (Jansen, 2006).
Task 1: two legged – open eyes
Task 2: two legged – closed eyes
Task 3: one legged – open eyes (left and right leg alternately)
Task 4: one legged – closed eyes (left and right leg alternately) – free leg at
the height of the ankle of the supporting leg
Task 5: one legged – opened eyes (left and right leg alternately) – free leg at
90° hip and knee flexion
Task 6: one legged – open eyes provocation (left and right alternately) - free
leg the height of the ankle of the supporting leg – displacement of the
platform of 20mm in the x-Axis – provocation from medial
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66
The order in which the tasks were performed was the same for all subjects and for
all experiment sessions. Each task was performed for a maximum of 30 seconds
and was repeated three times in a row. Between repetitions of identical trials,
subjects had a 90 second rest and between the different trials 150 seconds in order
to minimize the effects of fatigue. During the resting periods, subjects were sitting on
a chair.
The optimal performance was defined at a holding time of 30 seconds. When
subjects completed this, the trial was ended. Time was stopped if subjects touched
the ground with the free leg or had to grab the handrail and when they left the
platform.
The position of the supporting legs was standardized as much as possible. To be
able to do so, a scale was mounted to the plate that indicated the mid point of the
plate in both directions (Figure 5.3). For the two legged position, the foot was
positioned with the midpoint of the length of the foot on the medial-lateral axis of the
platform. The legs were ‘hip wide’ apart with each leg having the same distance
from the anterior-posterior axis of the platform.
Figure 5.3: Position on the ‘Posturomed®’ Platform for all two-legged tasks
For all one-legged tasks, the foot was placed in the middle of the plate with
reference to the anterior-posterior and the medial-lateral axis of the foot as well as of
with the platform (Figure 5.4). The position of each subject was recorded and used
again for all following measures.
After the positioning of the foot, the measurements commenced. After taking the
right position for the next task, the subjects had the possibility to stabilize their
5 Balance
67
position on the platform. When ready, the researcher would perform a countdown in
order to get the subject’s attention to the experiment. Only with the beginning of the
measurement, the subject would loosen the grip on the handrail and place the
hands on the hips. This assured a repeatable position for the balance tests.
Figure 5.4: Position on the ‘Posturomed®’ Platform for all one-legged tasks
For the trials with closed eyes, the subjects used a blindfold in order to ensure the
absence of vision for the complete task. In order to avoid injuries, a second person
stood right beside the platform and helped the subject when he lost their balance.
5.2.3 Statistics
The ability to stabilize body position on the ‘Posturomed®’ device was used to
quantify the effect of bed rest as well as the combination of bed rest and vibration
training on balance. The parameters were:
o
holding time of a certain position in seconds (s)
o
displacement of the platform per second in centimetres (cm)
For the holding time, the mean of the three trials for each task were calculated, then
pooled for all of the subjects and then compared using a t-test.
5 Balance
68
Displacement was measured by an accelerometer in mean distance of the sensor to
the origin of the platform in time. Here an increase in displacement indicates a
decrease in the ability to stabilize body position.
Level of significance was reached at α = 5%. Thus, values were considered to be
different when p < 0.05. Data analysis was performed using Statistica Softwear
(StatsSoft, Version 7.0). Additionally, the correlation between the parameters
‘holding time’ and ‘displacement of the platform’ was analysed. The correlation
between the two parameters, displacement and holding time, was calculated using
the same mean values as previously stated for holding time and displacement.
Correlation was calculated using the Pearson-Test.
5.2.4 Association with Data Loss
For the measure of displacement, some data points were lost due to a crash of the
computer system. This affected one session for two subjects. The missing data were
replaced by the values of the familiarization measurement. An impact on the
outcome of the results is not expected as this happened in the VBR 2 study phase
and the subjects knew the ‘Posturomed®’ system by that time. Also, the affected
subjects had very well developed balance ability and data analyses of the pre-bed
rest values from the VBR 1 study phase did not show a learning effect for these two
subjects. General effects on balance should not be affected as the lost trails only
represent 60 data points out of 1960. Holding time has not been affected as a
manual protocol for these values existed.
5.2.5 Malfunction of the Sensors of the ‘Posturomed®’
In 9 trials, displacement was not measured correctly in one of the two axes. The lost
data were compensated with the following formula:
Formula 1:
(value of the measured axis) ∗
2
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5.3
69
Results
5.3.1 Holding Time
For the analysis of holding time, the mean values of each task for all subjects were
calculated and then pooled. Figure 5.5 shows the mean values of holding time for all
subjects and all tasks.
Figure 5.5: Mean holding time (± Standard deviation) for all subjects and all tasks (n=48) in
seconds (s). Asterisk indicates a significant difference between the values (p = 0.01).
During the control intervention, the holding time did not change compared to pre-bed
rest values after 14 days of bed rest (Control: pre-bed rest: 25.8 ± 7.65 seconds /
post-bed rest: 25.5 ± 7.98 seconds). When subjects received vibration training
holding time decreased significantly from 27.0 ± 6.8 seconds to 25.6 ± 8.32 seconds
(p = 0.01)
The analysis of the individual tasks could indicate that not all tasks are affected by
bed rest (see Table 5.2). Significant differences in balance performance were only
detected in Task 4 ‘one-legged stand with closed eyes’ for the control (pre-bed rest
14.10 ± 7.15 s / post-bed rest: 11.33 ± 5.56 (p = 0.02)) and the vibration condition
(pre-bed rest 16.71 ± 9.29 s / post-bed rest: 11.94 ± 8.30 (p = 0.02)). All subjects
always completed fully the ‘two-legged stand’ task independently from visual control.
Results did not change due to bed rest. For the ‘one-legged’ conditions, increasing
standard deviations were noted.
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70
Table 5.2: Mean holding time ± Standard deviation for all subjects (n=8) and the 6 different
tasks. Values are shown for pre and post-bed rest during the control and the vibration
training intervention. Grey marked boxes indicate significant changes from pre to postbedrest values for the different interventions (control: p = 0.02 / vibration: p = 0.02).
Tasks
1
2
3
4
5
two legs
open eyes
two legs
closed eyes
one leg
open eyes
one leg
closed eyes
one leg
high
6 provocation
pre-HDT
control
post-HDT
control
pre-HDT
vibration
post-HDT
vibration
30 ± 0
30 ± 0
30 ± 0
30 ± 0
30 ± 0
30 ± 0
30 ± 0
30 ± 0
27.73 ± 5.58
27.90 ± 3.58
29.40 ± 1.78 29.62 ± 1.45
14.10 ± 7.15
11.33 ± 5.56
16.71 ± 9.29 11.94 ± 8.30
29.87 ± 0.48
29.65 ± 1.29
27.35 ± 5.76
28.83 ± 4.27
30 ± 0
28.42 ± 4.09
28.90 ± 2.92 28.19 ± 4.65
5.3.2 Displacement of the Platform
For the analysis of displacement of the platform, the mean values of each task for
each subject were calculated and then pooled. Thus, one mean value for each
subject per task went into the analysis. Figure 5.6 shows the mean values of
displacement of the platform for all subjects and all tasks.
During the control intervention, the displacement of the platform did not change from
pre to post-bed rest values (control: pre-bed rest: 3.62 ± 3.87 cm / post-bed rest:
4.13 ± 4.74 cm (p = 0.054). When subjects received vibration training during the
bed rest period, a significant increase in displacement of the platform of 22% was
noticed (vibration: pre-bed rest: 3.05 ± 3.27 cm / post-bed rest: 3.71 ± 4.71 (p =
0.01).
Analysis of the different tasks separately showed a significant difference in
displacement from pre to post-bed rest values for the control and the vibration
intervention (see Table 5.3) when performing ‘task 4 - one leg closed eyes’. No
other significant changes were found when analysing the different tasks.
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71
Figure 5.6: Mean holding time (±Standard deviation) for all subjects and all tasks (n = 48) in
seconds (s). Asterisks indicate a significant difference between the values.
Table 5.3: Mean displacement ± Standard deviation in cm/s for all subjects (n=8) and the 6
different tasks. Values are shown for pre and post-bed rest during the control and the
vibration training intervention. Grey marked boxes indicate significant changes from pre to
post-bed rest values for the different interventions (control: p = 0.03 / vibration: p = 0.02)
Tasks
two legs
1
pre-HDT
control
post-HDT
control
pre-HDT
vibration
post-HDT
vibration
0.32 ± 0.07
0.36 ± 0.08
0.32 ± 0.06
0.43 ± 0.1
0.47 ± 0.21
0.38 ± 0.11
0.50 ± 0.25
0.62 ± 0.27
2.37 ± 2.01
2.33 ± 1.64
1.93 ± 1.17
1.82 ± 0.92
9.65 ± 3.19
11.68 ± 2.89
8.07 ± 3.60
10.35 ± 4.37
1.88 ± 0.64
1.91 ± 0.60
1.81 ± 0.86
2.02 ± 0.83
3.84 ± 2.97
4.38 ± 4.62
3.04 ± 1.85
3.84 ± 3.12
open eyes
two legs
2
closed eyes
one leg
3
open eyes
one leg
4
closed eyes
one leg
5
high
6
provocation
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72
5.3.3 Correlation of the Parameters Displacement and Holding Time
The calculation of a correlation between the two parameters, displacement (cm) and
holding time (s) shows a high negative correlation for each of the measuring points
(Table 5.4).
Table 5.4: Correlation of displacement pro (s) in (cm) and holding time (s) for all subjects and
all tasks.
Control
Control
Vibration
Vibration
Pre-bed rest
Post-bed Rest
Pre-bed rest
Post-bed Rest
-0.93
-0.86
-0.87
-0.92
Correlation
displacement /
holding time
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5.4
73
Discussion
The results did not confirm the first hypothesis that 14-days of 6°-HDT bed rest
would negatively affect the ability to stabilize body position as measured with the
Posturomed®’ device. Contrary to our expectations, 14-days of immobilization did
not lead to negative effects on holding time and displacement of the platform. The
predicted correlation between the parameters displacement of the platform and
holding time of the tasks were confirmed.
Balance ability in the VBR-Study was measured with the Posturomed® using the
parameters holding time and displacement of the platform’. The Posturomed®
measures a very complex process on a systemic level. Although many components
contribute to the ability to keep balance, the Posturomed® only gives information
about the overall balance performance level of a subject. Negative effects of a
measure on some of the contributors to ‘balance ability’ may be compensated by
other components that are less affected. The sum of the activities of all contributors
may still result in the same total balance performance. This could be due to the
relatively short period of bed rest in addition to the fact that healthy subject were
investigated. A more detailed analysis, for example, on receptor activity or the
different reflex loops may have given another picture.
Figure 5.7: Organs and tissues contributing to the ability to keep a balanced body position.
In this experiment, it is only possible to estimate the effects of bed rest on the
contributing organs and tissues and how much this may have affected the result of
our study in comparing the data with other research literature.
The otolith-ocular reflex and thus the ocular counter-rolling certainly does have a
major impact on the ability to keep balance (Moore et al., 2001). This is supported
by the investigation of a significant decrease in the performance level for task 4 –
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74
one leg - closed eyes from pre-bed rest to post-bed rest values during the control
intervention. Vision serves the subject some reliability that may counteract physical
weaknesses. If the visual control is deactivated, the physical abilities get more
important and weaknesses may show up that have not been noticed before. It would
be interesting and important to actually measure how the different factors of balance
performance contributed to the results. However, this was not the main task of this
study and it was outside the scope of our methodology.
In this context, it should also be noted that the level of difficulty of the separate tasks
may not have been high enough. To fulfill a motor task, it needs certain physical
requirements. If an adequate level of, for example, fitness is achieved, one can
perform this task. But to be able to perform task 1 – two legged open eyes, the
motor capabilities are unlikely to be exhausted, meaning the capacity is much higher
than the requirements. In other words, the task is very easy for the subject. On the
other hand, if the task is so much below the actual capabilities, the capacity to
perform a task can become smaller; but on the performance level, this would not be
noticed, particularly with the methods used in this study. The performance of the
easy task does not change but the potential and ability to perform more difficult
tasks decreases.
In this study, the duration of the immobilization may not have been sufficient to
affect clearly balance performance so that it could have been adequately examined
with our set of test level. Healthy subjects who were still allowed to move within the
given bed rest requirements, were investigated. Consequently, our subjects were
more mobile in bed compared to injured or disabled patients for whom movement
may be completely reduced, for example, due to pain, bandage or casting.
Additionally, subjects walked a defined distance, twice daily, to the training room
and back. However, this procedure was important in order to be able to respond to
our hypothesis. Nevertheless, it may have led to a slower decrease in balance ability
as the body still received postural input twice a day.
The conditions of the bed rest study were very controlled and most importantly, the
subjects received a normo-caloric diet for the activity conditions they lived in during
the bed rest period (see Chapter 3 - General Methods). This may have contributed
to the observed effects on skeletal muscle that were much less than expected (see
Chapter 1 - Muscle Performance). As mentioned earlier, there is a strong
relationship between muscle atrophy and balance performance (Froböse et al.,
2003; Wilke et al., 2003). Decreases in skeletal muscle mass were observed in this
study; however, this did not affect muscle performance as much as expected.
5 Balance
75
Muscle performance does play a key role in balance performance and this may
explain the unchanged level of balance performance.
Our second hypothesis, that vibration training during 14-days HDT bed rest can
minimize the negative effects of immobilization on balance performance, was also
not confirmed. Holding time as well as displacement of the platform, showed
deterioration after 14-days of HDT-bed rest with vibration training rather than an
improvement in this area.
Our first hypothesis that bed rest would affect balance performance was not
supported by the results. A clearly negative effect of bed rest on balance
performance that could be counteracted by vibration training has not been found.
Moreover, vibration training even deteriorated the effect of bed rest on holding time
as well as displacement of the platform (Jansen, 2006). This result is surprising
given that many studies suggested a positive effect of vibration training on balance
(Bautmans et al., 2005; Bogaerts et al., 2006; Brunetti et al., 2006; Bruyere et al.,
2005; Cheung et al., 2003; Cheung et al., 2007; Gusi et al., 2006; Kawanabe et al.,
2007). However, with durations from 6 weeks up to 12 months of time for treatment
in these studies, they were a lot longer compared to our study. More importantly,
most elderly people (average age > 60) were investigated in previous studies
compared to young, healthy subjects in our study. Since the sensory motor system
showed a deterioration with aging at different levels of the sensory and motor
systems (Shaffer and Harrison, 2007; Shkuratova et al., 2004), it seems likely that
the age of the subjects has an impact on the outcome of a study. Presumably,
subjects in the previous studies started at a much lower balance performance level
than our subjects. With lower baseline performance levels and longer periods of
vibration training, it is more likely to improve balance performance than under the
conditions of the VBR-study. As discussed earlier, only 14 days of bed rest may not
have been long enough to affect significantly the balance performance in the control
group and to result in a significant compensatory training effect in the vibration
group. A study of Davis et al. (1997) also showed no effect after 5 days of bed rest
due to a training intervention compared to the control group (Davis et al., 1997)
which supports the finding that duration of the bed rest and intensity of the treatment
were not sufficient to cause a potential improvement for the vibration training group.
The vibration training did not just fail to counteract a bed rest effect, but it decreased
the level of balance performance as well. The measure of balance performance was
performed right after subjects finalized the bed rest period with the tilt table
experiment. The time point could be called ‘semi-acute’ as the last vibration training
session had been performed the day before. Thus, an adequate time for adaptation
5 Balance
76
was not given. A follow up measure would be desirable and should be applied in
future studies, but it is not available for the VRB-Study.
The sinusoidal signal from the vibration platform has been one of the few sensory
input signals the subjects received during the bed rest period. Subjects were barefooted and stood on the vibration platform with the whole sole of the foot. Especially
for the mechano-receptors that are located in the lower limb and under the sole of
the foot, which were closest to the vibration source, the vibration signal is a very
demanding input. The decreased balance ability could be the result of an irritation or
adaptation of the respective receptors to the vibration signal. This is especially true
for the Meissner corpuscles and the Pacinian corpuscles which are located in the
skin and are specifically sensitive to vibrations. These mechano receptors do not
typically belong to the proprioceptors but belong more to the cutaneous receptors
(Lundy-Eckman, 2002; Shaffer and Harrison, 2007). However, their input is very
important for the sensing of joint position as well as movement. For the receptors
under the sole of the foot, it could be shown that these receptors give information
about the site and the force of weight-bearing activities and they also can influence
muscle activity of the lower extremity (Burke et al., 1989; Kennedy and Inglis, 2002;
Lundy-Eckman, 2002; Perry, 2006; Robbins et al., 1995; Shaffer and Harrison,
2007). Since they are very sensitive to an adaptation in response to vibration
training, it is very likely and may be the reason for the decrease in balance ability
after the application during the bed rest period. However, due to our methods, we
can only speculate about this process. Longer studies may show different results
because the lower the level of balance performance becomes in response to
immobilization the more the effect of a vibration training application dominates over
the effect on the cutaneous receptors.
Other sensory organs, like the Golgi-Tendon organ or the muscle spindles, may
show the same effect of adaptation to the vibration training intervention. Muscle
spindles are very sensitive to stretch of the muscle and play an important role in
reflexive and voluntary movements as they provide afferent input to the central
nervous system (Prochazka, 1981; Shaffer and Harrison, 2007). As muscle spindles
are sensitive to aging (Shaffer and Harrison, 2007; Swash and Fox, 1972) and
immobilization (Anderson et al., 1999; Jozsa et al., 1988; Rosant et al., 2006) it is
likely that they are also sensitive to overload due to vibration stimulus during an
otherwise passive situation. Consequently, this could lead to deterioration when
performing the balance testing immediately after completing the bed rest period.
As expected, there is a high negative correlation between the two parameters
displacement and holding time. It is not surprising that with an increasing
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displacement of the platform, the holding time decreases. Thus, using the
Posturomed® device, the ability to stabilize the platform is well predictable for the
holding time to achieve a task and vice versa.
5.4.1 Limitations of the Design
5.4.1.1
Influence of Learning Effects
A great effort has been made to minimize the impact of learning effects on the
outcome measures (see 5.2.2). The balance performance level was heterogeneous
in the population of this study that made the practice session even more important,
especially for the subjects with a lower level of balance performance. Familiarization
and practice clearly minimized the learning effect. However, it could not avoid
differences in the performance levels of the subjects and thus in the sensibility to
respond with a change in balance performance due to bed rest. The heterogeneous
population may also have caused the high standard deviations observed, especially
in the one legged tasks. For future studies, an additional practise session should be
performed.
Data analysis showed that the holding time of a certain position was more sensitive
for learning effects than the displacement of the platform.
5.4.1.2
Order of the Tasks
The 1-6 order of the tasks was intentionally chosen by the investigators. The reason
for this was an increase in the level of difficulty so that the most difficult task was
positioned at the end of the experimental session. Only during the performance of
the experiment did it turn out that the subjects assessed the level of difficulty
differently. Task 4 ‘one leg, closed eyes’ was considered the most difficult task as
the visual control was missing. It was decided, however, to retain with the same
order for the rest of the study and for all subjects. Thus, if fatigue had an impact on
the balance performance of the subjects, it was the same for all subjects. The
separate analyses of the different tasks showed that ‘task 4’ in fact was the only one
that showed significant changes due to immobilization which was probably due to
the fact that it was the most demanding task.
5.4.1.3
Control Group
The decision to allow the subjects to train in an upright position was chosen
intentionally in order to get the highest degree of control of the training intervention
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(see chapter 3 - General Methods). However, it may have had an impact on the
results for the pre and post-bed rest values that reduced the difference in response
between the control and the vibration intervention group.
5.4.2 Conclusion and Future Work
In conclusion, both of the hypotheses could not be confirmed. However, the goal to
measure the effect of bed rest on balance with the Posturomed® was achieved and
well tolerated by the subjects. The results suggest that vibration training may be a
very demanding task for the cutaneous receptors as well as muscle spindles and
other proprioceptors. This aspect needs further investigation within the context of
vibration training.
The length of bed rest that was under very well controlled conditions used in this
study may not have been sufficient to significantly affect balance. Clearly, if vibration
training is to be applied over a long duration in space flight, the effects of vibration
training on all factors influencing the stability of body position should be further
investigated in order to be able to predict the range of effects on different structures
in the human body that can occur and to determine the advantages and
disadvantages of a training method.
6 Cartilage Health
79
6 Cartilage Health
6.1
Specific Background
Articular cartilage in synovial joints serves a variety of functions which include
providing joint congruency, transferring and distributing forces, and allowing joint
movement. A healthy biological and mechanical environment for cartilage is the
prerequisite for proper joint function. Typically, a change in the biological and/or
mechanical
environment
for
cartilage
leads
to
cartilage
degeneration
or
osteoarthritis. The most common location for osteoarthritis is the knee (Neame et
al., 2004). While the role of mechanobiological factors for healthy cartilage
development and maintenance have received much attention (Carter and Wong,
1988a; Wong et al., 1999; Wong and Carter, 1988) the effects of immobilization or
partial weight bearing after injuries and the effects of space flight on cartilage
biology and morphology in man are largely unknown.
6.1.1 Cartilage Morphology and Loading
Mechanobiological factors cause, throughout life, changes in articular cartilage
thickness distributions or cartilage morphology in a joint (Carter and Beaupre, 2001).
Cartilage morphology, for example when cartilage degrades and thus becomes
thinner, may be indicative of degenerative processes of cartilage (Phan et al., 2005).
Healthy articular cartilage tends to be thickest in joints, such as the knees, that
experience high forces. In addition, side differences in muscle cross sectional are
positively correlated with side differences in articular cartilage morphology (Eckstein
et al., 2002b). A recent study (Andriacchi et al., 2004) showed, that for healthy
knees, the ratio of medial to lateral cartilage is greater in individuals who have a
larger peak knee adduction moment during walking, suggesting that cartilage is
thicker in areas where the load is greater. These results support the animal studies
(Haapala et al., 1996; Haapala et al., 1999; Haapala et al., 2000; Jortikka et al.,
1997; Jurvelin et al., 1986; Kiviranta et al., 1988a; Kiviranta et al., 1994) where
articular cartilage increased in thickness by up to 19 to 23% (Kiviranta et al., 1988b)
when high mechanical loads were applied. An increase in cartilage thickness with
exposure to higher loads may be off-set by a greater cartilage surface that may be
caused by high physical activity during growth (Eckstein et al., 2002a; Muhlbauer et
al., 2000). Changes in tibio-femoral cartilage thickness are not dose dependent
suggesting that adult human cartilage properties may not be sensitive or improved
with training (Eckstein et al., 2005).
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80
Disuse induced changes in cartilage morphology and biology could be shown in
previous studies on animals as well as humans. A study on young beagle dogs
found decreases in proteoglycan concentration and compressive stiffness after 11
weeks of immobilization (Haapala et al., 2000; Jurvelin et al., 1986; Kiviranta et al.,
1988a). In this study, the right hind limbs of the dogs were immobilized at 90° flexion
of the knee and ankle joint with a fibreglass cast. Further investigations of the same
group showed that the immobilization induced cartilage softening was not fully
restorable (Haapala et al., 1999). In a different study, canine knees were
immobilized with a sling causing mechanical unloading but still allowing minimum
motion in the joint (Setton et al., 1997). The investigators found no changes in
proteoglycan and collagen content, cartilage stiffness or cartilage thickness (Setton
et al., 1997). The discrepancy of these results may have been due to the fact that
the type of immobilization played a role in the potential of the cartilage to recover
(Behrens et al., 1989). Only a few studies (Eckstein et al., 2002a; Hinterwimmer et
al., 2004; Muhlbauer et al., 2000; Vanwanseele et al., 2002; Vanwanseele et al.,
2003) have investigated the influence of mechanical unloading on articular cartilage
in humans. For instance, in paraplegic patients, cartilage thinning of up to 25% after
24 months has been observed (Vanwanseele et al., 2003). Hinterwimmer et al.
(Hinterwimmer et al., 2004) investigated the effect of 7 weeks of partial load bearing
on articular cartilage morphology changes in all knee compartments. Changes in
articular cartilage thickness for the different compartments ranged from -2.9 ± 3.2 %
for the patella to -6.6 ± 4.9% for the medial tibia.
6.1.2 Cartilage Oligometric Matrix Protein
Cartilage oligometric matrix protein (COMP) is a structural protein primarily found in
cartilage (Hedbom et al., 1992). COMP may also play a role in stabilizing the
extracellular matrix through its interaction with collagen fibrils and other matrix
components (Johnson et al., 2004; Mann et al., 2004). Changes in serum COMP
concentration have been associated with cartilage degradation (Neidhart et al.,
1997) and may be an indicator of cartilage catabolism (Jordan, 2005). Serum COMP
concentrations are elevated in patients with knee osteoarthritis (Clark et al., 1999)
and rheumatoid arthritis (Forslind et al., 1992). Cartilage, like other biological tissues
including skeletal muscle and bone, is sensitive to loading and disuse (Johnson,
1998; Smith et al., 1992b). For instance, elevated serum COMP concentrations
have been reported after a moderate walking exercise in healthy adults
(Mundermann et al., 2005) and after extensive running exercise in athletes (Neidhart
et al., 2000). Thus, serum COMP concentration appears to be sensitive to
6 Cartilage Health
81
physiological loading. Similarly, it has been suggested (Carter and Wong, 1988b;
Wong and Carter, 1988) that cyclic mechanical loading may play an important role in
regulating metabolic processes associated with the development, remodelling and
disease of biological tissues, including cartilage. In particular, the turnover of COMP
fragments may be an important mechanism for the regulation of tissue synthesis
and degradation (Giannoni et al., 2003; Wong et al., 1999).
The increasing number of patients with degenerative cartilage diseases, as well as,
for example, the prospect of a possible flight to Mars with an possible duration of
two to three years emphasizes the need for further research in the field of cartilage
health and mechanical unloading. One model for simulating physiological effects of
a microgravity environment on the human body on earth is bed rest in a 6°-headdown-tilt (HDT) position (Kakurin et al., 1976).
In an attempt to increase the efficiency of strength training that may affect all tissues
of the musculoskeletal system, in the past decade vibration training became very
popular as a complement to regular strength training (Jordan et al., 2005). During
whole body vibration training, the subject performs isometric or dynamic exercises
on a vibrating plate. Vibration frequencies between 15 Hz and 90Hz have been used
to either achieve adaptations in muscle or bone muscle (Issurin, 2005; Rubin et al.,
2002a). For instance, high frequency low amplitude vibration training has been
shown to increase osteogenesis of bone in animals (Rubin et al., 2001) and humans
(Rubin et al., 2002a; Rubin et al., 2002b). Thus, vibration training may have the
potential of reducing negative effects of unloading on biological tissues including
cartilage.
There is still a controversial debate whether articular cartilage is sensitive to
unloading and also if articular cartilage is able to recover after degradation. Also the
biological response of articular cartilage in healthy subjects to relatively short term
unloading during bed rest induced immobilization or spaceflight is still unknown.
Similarly, it is not known if possible effects of unloading on articular cartilage can be
avoided using a simple and time-efficient exercise regiment.
Therefore, the purpose of this study was to assess the influence of a vibration
training intervention on the morphological and biological changes on cartilage
associated with immobilization. To achieve this purpose the following hypotheses
were explored:
6 Cartilage Health
a)
82
14-days of head down tilt bed rest will lead to a reduction in cartilage
thickness loss,
b)
Vibration training will slow down or prevent the reduction in cartilage
thickness,
c)
14-days of head down tilt bed rest will lead to a reduction in serum
COMP concentrations,
d)
Vibration training will slow down or prevent the reduction in serum
COMP concentrations.
6 Cartilage Health
6.2
83
Specific Methods
6.2.1 MR-Imaging
The left knee of each subject was examined using a 1.5 Tesla magnetic resonance
imaging (MRI) scanner (Siemens Sonata, Erlangen, Germany). MRI data collection
was performed at the Cardio-MR Praxis, Krankenhaus Porz, Cologne, Germany.
Articular cartilage of the tibio-femoral joint was imaged in the sagittal plane before
and after the intervention or control phases. Images were taken on the last day (day
-1) of the adaptation period prior to bed rest and on day R1 in the recovery period
after the bed rest. Subjects walked a defined distance to the MR praxis, controlled
by the activity monitor. Imaging was performed at an in-plane resolution of 0.35 mm
x 0.35 mm, slice thickness 2mm, and an image matrix of 448 x 512 pixels. After data
collection, all images were segmented by one of the investigators. The investigator
was blinded to the order of the image acquisition (pre-HDT, post-HDT) and also to
the intervention (vibration training, control intervention).
6.2.2 Three-dimensional (3D) Cartilage Model
Cartilage in each slice of the MR images was segmented using a B-Spline Snake
algorithm with manual correction built into our custom software (Koo et al., 2005).
Once a user draws an initial boundary, the algorithm moves the boundary close to
the edges of cartilage. The MR images do not always have consistent brightness,
thus manual correction was required. The cartilage boundaries from all slices in a
MR image set were combined to create a 3D cartilage model using a volume
rendering technique (Koo et al., 2005), which fills the space between boundaries
obtained from adjacent slices and creates a polygonal surface model. The cartilage
model was divided into an articulating surface and cartilage-bone interface surface
to calculate cartilage thickness. For each point on the articulating surface, the
closest point on the cartilage-bone interface surface was found and the distance
between the two points was color-coded on the two points. The accuracy of the
cartilage thickness measurement using this method was verified in our previous
study (Koo et al., 2005). The cartilage model building process was performed by a
single observer to increase the reproducibility of the process. The coefficient of
variation (= standard deviation / mean * 100) of intra-observer reproducibility in
measuring average cartilage thickness of a weight bearing region over five
repetitions was 1.6%.
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6.2.3 Cartilage Thickness Measurement
The tibio-femoral contact areas in the femoral cartilage were divided into three
functional weight bearing regions for each condyle based on the knee flexion angle
during walking (Koo et al., 2005). The knee is flexed from 0 to 30 and 0 to 60
degrees during stance and swing phases of normal walking respectively. The flexion
angle can be less than 0 in the case of knee hyper extension. Thus we defined
anterior, middle and posterior weight bearing regions which match the tibio-femoral
contact regions at -30° to 0°, 0° to 30° and 30° to 60° of knee flexion angles
respectively (Figure 1). Average thickness was calculated for the load bearing
anterior, middle and posterior regions of the femur and the anterior and posterior
region of the tibia. Medial and lateral articulating surface of femur and tibia were
analysed.
6.2.4 Blood
Fasting blood samples were drawn at 7.00 am on days -3 and -1 in the adaptation
period, days 2, 6, 8, 11, 13, 14 of the intervention period and on day R2, R3 and R5
of the recovery period (Table 1). Blood was drawn by medical doctors using a short
catheter in serum monovettes (Sarstedt, Germany) from a antecubital vein. 150 µl
serum was aliquotted into Eppendorf tubes and frozen at -80°C until analysis.
Serum COMP concentration was analysed using a commercial enzyme-linked
immunosorbent assay (COMP® ELISA; AnaMar Medical AB, Lund Sweden).
Analysis was performed in duplicate. All samples of any subject of both study
phases were analysed on plates from the same batch of COMP® ELISAs. In
addition, all samples of any subjects were analysed on the same plate to avoid
differences in serum COMP concentration due to inter-assay variation.
6.2.5 Statistical Analysis
Statistical analyses were performed using STATISTICA software (StatSoft, Inc.,
Tulsa, USA). All results are shown as means ± SD. Differences in serum COMP
concentrations between days and phases were detected using repeated measure
analysis of variance (ANOVA) with phase as factor. Similarly, differences in cartilage
thickness before and after intervention and between phases were detected using
repeated measures ANOVA with phase as factor.
6 Cartilage Health
6.3
85
Results
6.3.1 Cartilage Thickness
Changes in average and maximum cartilage thickness after 14 day of 6°-HDT bed
rest were observed for the tibia but not for the lateral and medial compartments of
the femur (Table 6.1).
Table 6.1: Average values and changes in mean and maximum thickness (± SD) for the
mechanically loaded regions of articular cartilage in the knee pre and post 14 days of HDTbed rest (n=8).’d -1’ stands for day -1 in the recovery phase, d R1 for the first day in the
recovery phase. The asterisk indicates p-values < 0.05.
Compartment
Maximum Thickness
Mean Thickness
[mm]
[mm]
Control
Vibration
Control
Vibration
Tibia
pre-HDT (d -1)
5.02 ± 1.18
4.18 ± 1.03
3.08 ± 0.60
2.66 ± 0.45
post-HDT (d R1)
4.29 ± 1.25
5.25 ± 1.21
2.82 ± 0.60
3.24 ± 0.63
%change
-14.57*
26.61*
-8.3*
21.91*
pre-HDT (d -1)
3.70 ± 0.50
3.91 ± 0.52
2.37 ± 0.40
2.50 ± 0.24
post-HDT (d R1)
3.90 ± 0.74
3.97 ± 0.46
2.41 ± 0.30
2.52 ± 0.25
%change
5.32
1.58
-2.16
-5.90
pre-HDT (d -1)
3.73 ± 0.51
3.50 ± 0.86
2.36 ± 0.43
2.28 ± 0.22
post-HDT (d R1)
3.84 ± 0.50
3.40 ± 0.58
2.44 ± 0.32
2.30 ± 0.23
%change
2.70
-2.50
3.70
-2.51
Lateral Femur
Medial Femur
The rate of change in average and maximum cartilage thickness did not differ for the
medial and the lateral compartment as well as for the anterior and posterior region in
each compartment of the tibia for both phases (CON and VIB) so that all values for
the tibia were analysed as one compartment. When subjects received the control
intervention, average and maximum cartilage thickness decreased significantly
(average thickness: p = 0.025; maximum thickness: =0.015) after 14 days of bed
rest (maximum thickness: %-change = -14.57% (Figure 6.1), average thickness: %-
6 Cartilage Health
86
change -8.3 %). The opposite result was observed for the vibration training
condition. Average and maximum thickness in the tibial cartilage increased
significantly by 26.61% (maximum thickness) and 21.91% (average thickness).
Values in the lateral as well as the medial femoral cartilage for anterior, middle and
posterior regions did not show significant differences as a result of bed rest or the
training intervention.
7
cartilage thickness [mm]
6
*
*
5
pre
post
4
3
2
1
0
control
vibration
intervention
Figure 6.1: Absolute changes of cartilage thickness in the tibia from pre- to post-HDT-bed
rest for the control and the vibration condition (n = 8). Data are shown as mean of all
subjects with SD. *: p < 0.05.
6.3.2 Serum COMP Concentration
On adaptation day -3, mean serum COMP concentration was 7.02 ± 1.12 U/l for the
control phase (CON) and 7.23 ± 1.15 U/L for the intervention phase (VIB). With 6.80
± 1.41 U/L (CON) and 6.90 ± 0.95 U/L (VIB) at day -1 prior to bed rest, serum
COMP concentrations were stable for the baseline measurements. Serum COMP
concentration was in the range of normal distribution for healthy subjects (AnaMar
Medical AB, 2003).The first blood samples after 24 hours of 6°-HDT intervention
showed a significant decrease in serum COMP levels (CON: 5.80 ± 0.84 U/L; VIB:
6.20 ± 0.75 U/L (p = 0.022)) (Figure 6.2). Values decreased on average by 14.8%
6 Cartilage Health
87
when subjects received the control condition and by 10.1% for the vibration training
condition. However, there was no statistical difference in the response of serum
COMP concentration between the control and the vibration training condition. During
the 14-day 6°-HDT bed rest period the values stayed stable at lower levels for both
groups. No difference in the adaptation of the serum COMP concentration due to the
training intervention could be observed throughout the period of bed rest. Serum
COMP concentration for both phases returned to baseline levels after subjects were
mobile again (CON: 6.78 ± 0.91 U/L (+ 28.6%), VIB: 6.96 ± 0.94 U/L (+ 26%): (p <
0.001)) and remained stable at higher levels for the recovery period.
9
COMP (U/L)
8
*
*
HDT VIB
HDT CON
7
6
5
4
0
-3
-1
2
6
8
11
14
R2
R3
R5
days
Figure 6.2: Average changes in serum COMP concentration in response to 6°-HDT bed rest
and vibration training (n=8). Serum COMP concentration decreased significantly (p = 0.022)
after 24h of bed rest and returned to baseline levels after subjects were mobile again (p =
0.001).
6 Cartilage Health
6.4
88
Discussion
The data show that 14-days of HDT bed rest lead to a significant loss in cartilage
thickness in the tibia as well as systemic serum COMP concentration. The applied
vibration training protocol appears to prevent the loss of cartilage thickness and, the
reduction in serum COMP concentration could not be prevented.
This is the first study to investigate the adaptation of articular cartilage in the knee to
a short period of immobilization in healthy young subjects. We hypothesized that a
14 day bed rest immobilization will lead to a reduction in cartilage thickness and
serum COMP concentration and secondly, that vibration training may be beneficial
to prevent a reduction in cartilage thickness and serum COMP concentration. Our
results show that, after only 14 days of immobilization through bed rest, cartilage
thinning at the knee can be observed. When subjects received vibration training
twice a day, cartilage thickness at the knee increased.
Cartilage thinning in our study was only significant in the tibia compared to previous
studies (Hinterwimmer et al., 2004; Vanwanseele et al., 2002) that reported changes
in all cartilage compartments at the knee. However, Hinterwimmer et al.
(Hinterwimmer et al., 2004) and Vanwanseele et al. (Vanwanseele et al., 2002) also
found that changes of articular cartilage thickness were more pronounced in the tibia
than in the femur. Different results for both the tibia and the femur are not surprising
considering that, due to the anatomy of the knee joint, the load bearing area of the
tibial plateau is much smaller compared to the femur head for knee flexion angles
between 0° and 60°. This contributes to higher stress rates in the tibia when the joint
is mechanically loaded and may also cause a stronger response of the tibia to
unloading.
In the current study, cartilage thinning was similar for the medial and lateral tibia
compartments in contrast to previous studies (Hinterwimmer et al., 2004;
Vanwanseele et al., 2002). A possible explanation may be the short amount of time
that our subjects were exposed to immobilization compared to those in previous
studies. This time period may not have been long enough to develop different
adaptations in different compartments.
The subjects in this study had no history of knee injury and no cartilage lesions were
detected in the MR images. Subjects were ‘mobile’ during the bed rest period. This
meant that they were allowed to move their joints and to turn around to lie on their
back, front or on their side as long as they did not leave the 6°-HDT position. In
addition, subjects walked a defined path to the training room leading to cyclic
loading of cartilage possibly stimulating metabolic activity. Patients who are
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89
immobile after injury or surgery are usually under pain and thus move their joints
even less than our subjects. It may be that changes in cartilage thickness in these
patients would be even more pronounced.
Because cartilage is an avascular, aneural and alymphatic tissue, mechanical
stimulation is, besides diffusion, the only signal pathway from the periphery to the
chondrocytes. The extracellular matrix functions as the signal transmitter which
transfers mechanical signals to the chondrocytes. In response, chondrocytes
change their metabolic activity (Martinek, 2003). It has also been shown previously,
that unloading cartilage changes proteoglycan synthesis (Gray et al., 1988) resulting
in altered mechanical properties of the tissue. Proteoglycans are negatively charged
and therefore exert a large swelling pressure that causes tensile stress on the
surrounding collagen network (Maroudas, 1976). If unloading of a joint can lead to
changes in proteoglycan content, this may result in different hydration of cartilage.
Thus, the measured decrease in cartilage thickness for the control condition and the
increase for the vibration training intervention may not necessarily reflect a loss in
cartilage tissue but a change in the mechanical properties of cartilage, due to an
altered hydrostatic pressure. However, the imaging technique used in this study only
detects quantitative changes in cartilage thickness and provides no information
about the quality of the cartilage tissue.
The mean and maximal thicknesses of the knee cartilage were quantified from MR
images. They were taken in the sagittal plane, which did not allow for the accurate
segmentation of the marginal areas. Additionally, we did not determine cartilage
thickness of the patella. In contrast to previous studies (Hinterwimmer et al., 2004;
Muhlbauer et al., 2000; Vanwanseele et al., 2002) that investigated changes in
cartilage thickness over the entire surface under various conditions, we chose to
measure cartilage thickness only in the load-bearing regions of articular cartilage.
Therefore, our technique of using sagittal plane images was appropriate. In activities
of daily living, the flexion angle of the tibio-femoral joint ranges between 0° and 60°.
This corresponds to certain regions of the cartilage surface that are more frequently
in contact with the congruent joint surface than others. Most likely, regions that are
often more exposed to mechanical loading in every day life are more sensitive to
unloading than regions that are generally not exposed to loading. This phenomenon
can be compared with bone mineral content in mechanically loaded bones as
compared, for example, to arm or shoulder bones. Loss in bone mineral content,
due to unloading, is more pronounced in bones that are usually exposed to
mechanical loading (Uebelhart et al., 2000). Similarly, for articular cartilage, a
greater response to unloading in cartilage regions that are loaded during normal
6 Cartilage Health
90
joint motions than in normally unloaded regions may be expected. If usually loaded
regions are more sensitive to unloading, then this may explain the greater range of
change in mean cartilage thickness in our study compared to previous studies
(Hinterwimmer et al., 2004; Vanwanseele et al., 2002).
The results of this study show that a short term bed rest at 6°-HDT results in a
reduction in serum COMP concentration within less than two days indicating that
COMP is sensitive to unloading. One possible explanation for this reduction in
serum COMP concentration is a decreased diffusion of COMP molecules from the
cartilage into serum due to a lack of exposure of the joint to cyclic movement and
loading. This possibility is supported by the fact that serum COMP concentrations
returned to baseline within 24 hours following bed rest. Previous studies also found
the sensitivity of COMP to mechanical loading (Jortikka et al., 1997; Neidhart et al.,
2000; Wong et al., 1999). Our results support findings in marathon runners (Neidhart
et al., 2000) and healthy subjects after walking exercises (Mundermann et al., 2005)
who both found increases in serum COMP concentration in healthy subjects after
exercise and thus stated the sensitivity of COMP to mechanical loading. This would
lead to the conclusion that unloading should also affect serum COMP concentration.
With our results, we could show deceases of serum COMP in the absence of joint
loading.
Another possible explanation for the reduction in serum COMP concentration during
bed rest is a change in cartilage metabolism in response to the lack of mechanical
stimulus during this period. Wong et al. (Wong et al., 1999) earlier reported a cyclic
compression in vitro results in an up-regulation of protein synthesis. They stated that
chondrocytes had the ability to sense stress or strain in the extracellular
environment that resulted in an alteration of the expression of matrix proteins.
Moving the knee joint causes hydrostatic stress and strain within the cartilage tissue
of the knee joint. During our bed rest study, movement of the joint was reduced to a
minimum due to the immobilization. Consequently, stress and strain in knee
cartilage was likely to be reduced that possibly lead to a slower metabolism and thus
reduce the turn-over of COMP.
The vibration training intervention did not have a different effect on serum COMP
concentration than the control intervention. Despite its benefits for general physical
conditioning (Cardinale and Wakeling, 2005), the vibration training intervention used
in this study with the goal to avoid the effects of prolonged bed rest may not have
been sufficient in magnitude and/or duration to cause any significant changes in
serum COMP concentration compared to the control intervention.
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91
Scientific investigations of the effects of vibration training in a controlled study
design are rare. The physiological response mechanisms caused by vibration
training are largely unknown. The current study was a first attempt in quantifying the
effect of arbitrary vibration training on cartilage in vivo. Secondly, different biological
tissues, including cartilage, bone, muscle, ligaments, and tendons, may respond
differently to the various combinations of vibration frequency, amplitude, training
duration, and number of vibration bouts and thus, a training regime that is beneficial
to muscle may not affect COMP turnover. Another aspect may be that the effect of
immobilization on serum COMP concentration is greater than a possible effect of
vibration training to counteract this effect. This may be caused by the amount of
cartilage that is affected by bed rest compared to articular cartilage that is affected
by the vibration training. Therefore, possibly only a more demanding training
protocol would lead to changes in serum COMP concentrations systemically
measured in blood.
Vibration training had an effect on cartilage thickness but not on serum COMP
concentrations. This result is not necessarily controversial. It may well be that the
decrease in serum COMP concentration was caused by reduced diffusion of COMP
molecules into the blood due to no movement of the joint. Cartilage thickness on the
other hand, was maintained due to a mechanical stimulus that is load dependent.
Thus thickness maintenance may not require flexion-extension movement.
In summary, the results of this study suggest that articular cartilage thickness is
sensitive to unloading and vibration training may be a potent countermeasure
against these effects. Future research should strive to reveal the physiological
processes that lead to the results that have been observed in this study.
Additionally, the potential of the recovery of cartilage thinning in man after confined
immobilization is still unknown. Serum COMP concentration is sensitive to unloading
during bed rest. While COMP is a structural protein that reflects the state of
cartilage, future research should investigate the effect of unloading on cartilage
metabolism with the ultimate goal to minimize negative effects of bed rest or other
models of unloading, such as space flight, on cartilage health. Understanding and
quantifying the mechanical response of articular cartilage to its physical environment
in healthy subjects may help to develop countermeasures to prevent cartilage
thinning after prolonged bed rest due to illness or surgery. Until countermeasures
have been developed, cartilage health has to be considered when patients start to
load their joints again after mid-term or long-term bed rest and for astronauts upon
their return to earth after a lengthy space flight.
7 General Discussion
92
The general purpose of the Vibration-Bed-Rest-Study was to investigate the effects
of 14-days of 6°-head-down-tilt bed rest on the human body in an integrative
approach and to test whether vibration training could counteract the effects of
immobilization on different systems and tissues of the human body. The results
should provide a recommendation whether vibration training may serve as an
appropriate countermeasure in the scope of space flight.
Although HDT bed rest is a well established model to simulate the physiological
effects of microgravity, the comparability of the population of students we examined
in the VBR-Study with the population of astronauts may be difficult. These two
populations may differ, for instance, in age and physical fitness, which would both
impact the responsiveness to training. We are well aware of the differences of these
two populations; however the problem cannot be resolved. Thus, the here presented
results of the VBR-Study represent the effects investigated in our group of subjects.
However, one should be aware of the earlier described constraints of inferential
statistics (see chapter 3.8 - General Statistics). The transfer of the results into the
application in space should only be conducted with the given limitations.
The first hypothesis that 14 days of HDT would lead to a general deconditioning of
the human body could not, in general, be confirmed for all physiological parameters
examined in this thesis.
A decrease in muscle performance was only given for the MVC and power of the
knee flexors, whereas the extensors were not significantly affected. As discussed in
chapter 4, there may be several reasons. Most importantly, subjects had different
fitness levels prior to the bed rest study. Although there was an attempt to choose a
homogenous group of subjects regarding the training status, this was not fully
achieved. That is because not only the absolute fitness level plays a role, but also
the activity level in normal daily life. Since subjects were only immobilized for 14
days, the different fitness levels may have had an impact on the velocity and relative
degree of weakening in adaptation to disuse. When using longer periods of bed rest,
this effect will loose significance since sooner or later atrophic processes will be
initiated independently in every subject from the previous fitness level.
The examination of balance performance showed similar results. Subjects did not
indicate the expected decreases in balance performance as described in chapter 5.
Levels of balance performance were different before the study, ranging from high to
low balance skills. Decreases in the performance level only became obvious when
subjects had to perform very challenging tasks, which may be an indicator for the
93
onset of degenerative processes concerning balance performance. For this
experiment a longer period of immobilization may have possibly resulted in a
different outcome. Moreover, the walk to and back from the training room twice daily
may have impacted more than expected, the response of balance performance to
bed rest.
The fact that 14 days of bed rest under very controlled conditions did not affect
muscle and balance performance in general showed the importance of a high level
of standardization of study protocols, especially with respect to diet, body position
and experiments during the bed rest period that may have an impact on the
adaptation of muscle and balance performance. The results showed how much the
response depended on the individual subject and muscle that was investigated.
The approach to investigate knee cartilage morphology with respect to space flight
or immobilization of healthy subjects was fairly new. The results indicated that
changes due to bed rest did occur; however further research has to be performed to
really understand the findings and their underlying mechanisms. So far, the
decrease in cartilage thickness of the weight bearing regions of the tibia fits into the
concept of degenerative processes in response to immobilization of the human
body.
Regarding our second hypothesis, that vibration training has the potential to
counteract the effects of 14 days of bed rest, the difficulty was that our first
hypothesis generally could not be confirmed. Consequently, vibration training could
not act as a countermeasure since the expected degenerative processes did not
occur. However, the training protocol and the training intensity were not designed in
order to increase muscle or balance performance but to minimize the rate of
degeneration. Thus, it did not seem surprising that vibration training did not lead to a
change in the response to bed rest, when the specific system did not show
degeneration, for example, the MVC for knee extensor muscles. The deterioration of
the bed rest effects that could be observed for balance performance as well as for
power and MVC of the knee flexors had not been expected before. Again, this may
have been due to the length of the investigation and the days of the experiments.
Compared to the differences in fitness levels among the subjects, the training
protocol that was applied seems to fail individualization. Additionally, the training
intensity was not adapted progressively throughout the bed rest period which we
would now recommend, based on the results of our investigation.
In general, for the testing of training measures in the scope of bed rest studies
longer duration of immobilization should be considered. This would favour both the
deconditioning as well as the training processes that are both critical for the
94
outcome of the study. In the VBR-Study it had been expected, that the 14 days of
immobilization would lead to a general deconditioning in all subjects, however this
was not the case. The assumption, that a general deconditioning would occur,
resulted in the general development of a training protocol that should not overload
our subjects, but adequately counteract the bed rest effects. As this deconditioning
was missing in some parts, the training intensity was not appropriate to impact the
performance levels anymore. The individual tailoring of the training protocol
represents another important variable for the outcome. In future studies, a more site
specific training should be considered compared to the general whole body vibration
training in this study. This would result in the use of regular strength training
exercises on a vibration platform that are muscle specific.
Based on the results of the VBR-Study and its predetermined conditions, a general
recommendation for a vibration training protocol that can counteract bed rest
induced changes in muscle and balance performance, as well as cartilage
morphology and biology, cannot be given, but potential remains that whole body
vibration can positively change the responsiveness to resistance training. However,
controlling the training intensity that leads to anabolic responses in the human body
is not trivial and needs a high level of individualization. It should be necessary to
consider the initial training status during recruiting and screening the subjects.
Within this focus, a homogeneous group of subjects should be aspired. Generally,
higher training intensities are recommended that are tailored to the individual
performance levels as well as the individual responses to the bed rest intervention.
Consequently, future studies are needed in order to optimize countermeasures for
bed rest induced degradation of tissues of the human organism.
8 Summary
95
8 Summary
The Vibration-Bed-Rest-Study (VBR-Study) was performed to investigate the
potential of whole body vibration training to counteract degenerative effects of 14
days of 6° head down tilt bed rest (6°-HDT bed rest) on the human body. The effects
of immobilization with and without vibration training on different tissues and organs,
including skeletal muscle performance, balance performance and articular cartilage,
were determined. The following general hypotheses were tested:
a) 14 days of 6°-HDT bed rest lead do a general deconditioning of the human
body.
b) Vibration training has the potential to counteract deconditioning during 14days of 6°-HDT bed rest in terms of slowing down the effects or even
preventing them.
In this thesis, the results of the following experiments were presented and
discussed:
o
Skeletal Muscle Performance (Chapter 4),
o
Balance Performance (Chapter 5),
o
Cartilage biology and morphology (Chapter 6).
Eight healthy male subjects (age: 26 ± 5 years; mass: 78 ± 10 kg; height: 179 ± 10
cm) participated in the study after giving their informed consent. The study was
performed in a cross-over-design where each subject received vibration training in
one phase and a control intervention in the other. During the training intervention,
subjects trained 2 x 5 minutes per day at 20 Hz with ~ 3 mm amplitude on a
vibration plate (Galileo 900). Subjects walked a defined path to the training room
and back twice daily. The schedules during the control and the vibration intervention
were identical except for the vibration of the plate. By this study design we were able
to interpret the real ‘vibration effect’. The experiments on muscle performance,
balance performance and cartilage morphology were scheduled before and after the
14 days of 6°-HDT bed rest. Blood sampling for the analysis of biomarkers was
done regularly at predefined times during the whole study.
Muscle performance was measured in maximum voluntary contraction (MVC) and
maximal power. MVC did not change due to bed rest for the knee flexor and knee
extensor muscles. When subjects received vibration training there was a significant
decrease in MVC for the knee flexor muscles, but not for the knee extensor
muscles. Maximal power did not change due to bed rest for the knee flexor muscles.
However, there was a significant decrease in maximal power of the knee flexors
when subjects received vibration training. In the knee extensors, bed rest lead to a
8 Summary
96
significant decrease in maximal power which could be prevented by vibration
training. The results indicated that changes in MVC and power after 14 days of 6°HDT bed rest under the given conditions were muscle and subject specific and may
have depended on their initial physical status. In reference to the power of the knee
extensors, the used training protocol was sufficient to cause a significant difference
in bed rest effects with and without training. Thus, vibration training with the protocol
used had the potential to affect the response of muscle to bed rest induced
immobilization.
Balance performance was measured with the Posturomed® device, using the
parameters ‘holding time’ and ‘displacement’. Bed rest did not lead to a general
deterioration in both parameters. Vibration training lead to a significant decrease in
holding time and an increased in displacement of the Posturomed®, which reflected
a decline in the performance level. The results may have been impacted by the early
point in time of the measurement, which did not allow for adaptation to the training
process, in addition to the relatively short duration of the bed rest and the training
period. Also, vibration training is a very complex and demanding input for our
postural receptor system and the central nervous system, which may possibly have
caused an acute disorientation that lead to the results.
Articular cartilage thickness was measured using magnet resonance imaging (MRI)
of the right knee. Additionally, serum concentrations of ‘Cartilage oligometric matrix
protein’ (COMP) were analysed from 10 blood samples taken throughout the study.
Decreases in average and maximum cartilage thickness after bed rest were
observed for the tibial condyle and the effects inverted into an increase when
subjects received vibration training. No changes were obtained for the femoral
condyle. After 24h of 6°-HDT bed rest, serum COMP concentration decreased
significantly and the values returned to baseline after bed rest. Vibration training did
not alter the response of serum COMP concentrations. This study showed that
decreases in cartilage thickness after a 14-day bed rest can be observed and that
vibration training may be able to counteract this effect. Changes in cartilage
thickness could reflect a change in mechanical properties of articular cartilage due
to the bed rest and the control intervention. Bed rest resulted in a reduction of serum
COMP concentrations within less than two days which might have been caused by
decreased diffusion of COMP molecules from the cartilage into serum due and / or
might reflect a change in cartilage metabolism in response to a lack of exposure of
the joint to mechanical loading.
Summarizing
the
results,
our
general
hypotheses
were
not
completely
substantiated. It can be stated that the degenerative effects of immobilization did not
8 Summary
97
reach the degree that was previously expected. Amongst others, the effect of the
very controlled study conditions, the normo-caloric diet and the allowance to stand
up and walk to the training room and back twice a day might have contributed to this
outcome. Also, the pre-study training status may impact the bed rest effects more
than expected. The training intensity was chosen in order to prevent or decelerate
the de-conditioning of the human body due to bed rest. As this deconditioning was
missing in some parts, the training intensity was not appropriate to impact the bed
rest effects anymore. The observed decline in performance due to the vibration
training has not been expected before.
Based on the findings of the VBR-Study, we cannot recommend generally pure
vibration training as a countermeasure for changes in muscle performance, balance
performance and articular cartilage morphology. For the latter, our results showed
that cartilage in the knee joint is responsive to both unloading and vibration training.
However, further research is encouraged in order to specify the responses. It is
likely that the combination of whole body vibration with resistance training will lead
to more promising results. Additionally, we suggest considering the initial training
status when recruiting and screening subjects. With this in focus, a homogeneous
group of subjects should be aspired. Generally, higher training intensities are
recommended, in addition to an individually tailored vibration training protocol for
each subject with a progressively increasing training intensity.
9 Zusammenfassung
98
9 Zusammenfassung
Im Rahmen der ‚Vibration-Bed-Rest-Study’ (VBR-Studie) wurde der Einsatz von
Vibrationstraining als Gegenmaßnahme für die degenerativen Auswirkungen von
Bettruhe in 6°-Kopftieflage (6°-head-down-tilt (6°-HDT)) untersucht. Dazu wurden 8
Probanden für 14 Tage in Bettruhe mit 6°-HDT immobilisiert. Die Auswirkungen von
Bettruhe mit und ohne Einsatz von Vibrationstraining auf unterschiedliche Gewebe
und Organe wurden untersucht, darunter z.B. die muskuläre Leistungsfähigkeit, die
Gleichgewichtsfähigkeit,
sowie
Gelenkknorpel
im
Knie.
Gegenstand
der
Untersuchung waren die folgenden allgemeinen Hypothesen:
a) 14
Tage
HDT-Bettruhe
führen
zu
einer
allgemeinen
Dekonditionierung des menschlichen Körpers.
b) Die Anwendung von Vibrationstraining während 14-tägiger Bettruhe
in 6°-HDT kann dieser Dekonditionierung entgegenwirken. Das zeigt
sich in einer Verlangsamung oder Aufhebung der zuvor beobachteten
Effekte.
In dieser Dissertation werden die Ergebnisse der folgenden Untersuchungen
präsentiert und diskutiert:
- Muskuläre Leistungsfähigkeit der unteren Extremität (Kapitel 4)
- Gleichgewichtsfähigkeit (Kapitel 5)
- Gelenkknorpelbiologie und –morphologie (Kapitel 6)
Acht gesunde männliche Probanden (Alter: 26 ± 5 Jahre; Gewicht: 78 ± 10 kg;
Größe: 179 ± 10 cm) nahmen an der VBR-Studie teil, die im ‚Crossover-Design’ mit
zwei Studienphasen durchgeführt wurde. Jeder Proband erhielt in einer Phase
Vibrationstraining und in der zweiten Phase eine Kontrollintervention. Während der
Trainingsintervention in der Bettruhephase trainierten die Probanden 2 mal täglich
für 5 mal 60 Sekunden auf der Vibrationsplatte (Galileo900) bei ein Frequenz von 20
Hz und einer Amplitude von ~ 3 mm. Die Strecke zum und vom Trainingsraum
wurde zweimal täglich gegangen. Die Abläufe waren identisch für die Kontroll- und
die Trainingsintervention, lediglich die Vibrationsplatte wurde während der
Kontrollintervention nicht angestellt. Dieses Studiendesign ermöglichte es daher,
den isolierten „Vibrations-Effekt“ zu untersuchen. Die Experimente zur muskulären
Leistungsfähigkeit, Gleichgewichtsfähigkeit und Kniegelenksknorpel wurden jeweils
vor und nach der Bettruheintervention durchgeführt. Blutabnahmen für Biomarker
fanden in regelmäßigen Abständen während der gesamten Untersuchung statt.
Die Kraftleistungsdiagnostik zeigte keine Veränderungen in der Maximalkraft der
Kniebeuger und Kniestrecker durch Bettruhe. Vibrationstraining führte zu einer
9 Zusammenfassung
99
Verschlechterung der Maximalkraft in den Kniebeugern, nicht aber in den
Kniestreckern.
Die
maximale
Leistung
zeigte
in
den
Kniebeugern
keine
Veränderung durch Bettruhe, Vibrationstraining veränderte das Ergebnis nicht. In
den Kniestreckern nahm die maximale Leistung nach Bettruhe signifikant ab, was
durch Vibrationstraining aufgehalten werden konnte. Die Ergebnisse zeigten, dass
eine Veränderung der Maximalkraft sowie der maximalen Leistung nach einer 14tägigen Bettruhe unter den gegebenen kontrollierten Bedingungen sehr muskel- und
probandenspezifisch auftritt, was an der initialen Leistungsfähigkeit liegen kann.
Betrachtet man die maximale Leistung, so konnte Vibrationstraining den
Bettruheeffekt für die Kniestrecker signifikant beeinflussen.
Die Gleichgewichtsfähigkeit wurde mit Hilfe des Posturomed® untersucht, die
Messgrößen waren die Haltezeit und die Auslenkung des Posturomed® bei der
Ausübung
vorgegebener
Übungen.
Bettruhe
führte
zu
keiner
generellen
Veränderung in beiden Parametern. Wurde Vibrationstraining angewendet, so
verschlechterten sich Haltezeit und Auslenkung signifikant. Beide Ergebnisse
stützen die Ausgangshypothese nicht, dass Bettruhe zu einer Abnahme der
Gleichgewichtsfähigkeit führt. Im Gegenteil, Vibrationstraining verschlechterte den
Bettruhe-Effekt. Als Grund kann der frühe Messzeitpunkt genannt werden, der keine
adäquate Zeit zu einer Trainingsanpassung zuließ, zusätzlich zu der relativ kurzen
Bettruhe- und Trainingsintervention. Außerdem stellt Vibrationstraining einen sehr
komplexen und anspruchsvollen Reiz für die Propriozeptoren und das zentrale
Nervensystem dar, was zu einer akuten Irritation führen kann.
Knorpeldicke wurde mit Hilfe der bildgebenden Magnet Resonanz (Magnet
Resonance
Imaging
(MRI))
gemessen.
Zusätzlich
wurden
die
Serum-
Konzentrationen von ‚Cartilage Oligometric Matrix Protein’ (COMP) untersucht. Eine
Abnahme der mittleren sowie der maximalen Knorpeldicke nach 14.Tagen Bettruhe
konnte an den Tibia-Kondylen festgestellt werden, nicht aber für den Femur.
Vibrationstraining führte zu einer Zunahme der mittleren und maximalen
Knorpeldicken. Serum-COMP-Konzentrationen nahmen nach 24 Stunden in
Bettruhe signifikant ab und stiegen direkt nach der Bettruhe wieder auf das
Ausgangsniveau an. Vibrationstraining veränderte diese Reaktion nicht.
Die
Ergebnisse
der
Knorpeluntersuchungen
zeigten
eine
Abnahme
der
Knorpeldicke in der Tibia und eine Umkehr des Effektes durch Vibrationstraining,
was auf eine Veränderung in den mechanischen Eigenschaften von Knorpel durch
die Kontroll- sowie die Trainingsintervention zurückzuführen sein könnte. Die
Veränderungen der Serum-COMP-Konzentration ist möglicherweise auf veränderte
Transportbedingungen der Fragmente aus dem Gelenk zurückzuführen und könnte
9 Zusammenfassung
100
auf eine Veränderung im Knorpelstoffwechsel durch die mangelnde mechanische
Belastung in Bettruhe hinweisen.
Zusammenfassend konnten die allgemeinen Hypothesen der Untersuchung nicht
vollständig bestätigt werden. Degenerative Veränderungen durch 14 Tage in HDTBettruhe konnten für muskuläre Leistungsfähigkeit, Gleichgewichtsfähigkeit und
Kniegelenksknorpel mit den hier angewendeten Methoden nicht in dem erwarteten
Ausmaß festgestellt werden, beziehungsweise waren parameter- und probandenspezifisch sehr unterschiedlich. Die Gründe dafür können vielfältig sein, beigetragen
dazu haben sicher die sehr kontrollierten Bedingungen, der ausgeglichene
Energiehaushalt, das Aufstehen, um zum Trainingsraum zu laufen, sowie der initiale
Trainingszustand der Probanden. Das Vibrationstraining wurde in seiner Intensität
so gewählt, dass es Organe und Gewebe vor Degeneration bewahren oder den
Prozess verlangsamen sollte. Die zum Teil ausbleibende Degeneration führte dazu,
dass der Trainingsreiz unter Umständen nicht mehr angemessen war. Wenn
Bettruhe keinen negativen Effekt auf das jeweilige System hatte, so konnte
Vibrationstraining dann auch nicht mehr als Gegenmaßnahme wirken. Die zum Teil
gefundenen negativen Effekte waren so nicht erwartet worden.
Auf Grundlage der hier vorgestellten Ergebnisse kann isoliertes Vibrationstraining
nicht generell als Gegenmaßnahme für Effekte von Bettruhe in 6°-HDT auf
muskuläre
Leistungsfähigkeit,
Gleichgewichtsfähigkeit
und
Gelenkknorpel
empfohlen werden. Dennoch sollten weitere Untersuchungen folgen, um die
Kombination von Vibrationstraining mit herkömmlichen Krafttrainingsmethoden im
Rahmen von Bettruhestudien zu untersuchen, und um die Ergebnisse für
Gelenkknorpel zu spezifizieren. Dabei sollte schon im Auswahlprozess der
Probanden dem initialen Trainingsniveau gesteigerte Beachtung geschenkt werden.
Wünschenswert
wäre
eine
bezüglich
des
Leistungsniveaus
homogene
Probandengruppe. Generell sind höhere Intensitäten in der Trainingsplanung
empfehlenswert und im Weiteren sollte der Schwerpunkt zukünftig auf eine
individuellere, progressive Steigerung der Trainingsintensität im Rahmen von
Bettruhestudien gelegt werden.
10 References
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Jarvinen, T. L., Jarvinen, M., Oja, P., Vuori, I., (2002a). Effect of a vibration exposure
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S., Jarvinen, T. L., Jarvinen, M., Oja, P., Vuori, I., (2002b). Effect of four-month
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202. Torvinen, S., Kannus, P., Sievanen, H., Jarvinen, T. A., Pasanen, M., Kontulainen,
S., Nenonen, A., Jarvinen, T. L., Paakkala, T., Jarvinen, M., Vuori, I., (2003). Effect
of 8-month vertical whole body vibration on bone, muscle performance, and body
balance: a randomized controlled study. J Bone Miner.Res. 18, 876-884.
203. Trappe, T. A., Lindquist, D. M., Carrithers, J. A., (2001). Muscle-specific atrophy of
the quadriceps femoris with aging. J.Appl.Physiol 90, 2070-2074.
204. Turbanski, S., Haas, C. T., Schmidtbleicher, D., Friedrich, A., Duisberg, P., (2005).
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205. Uebelhart, D., Bernard, J., Hartmann, D. J., Moro, L., Roth, M., Uebelhart, B.,
Rehailia, M., Mauco, G., Schmitt, D. A., Alexandre, C., Vico, L., (2000). Modifications
of bone and connective tissue after orthostatic bedrest. Osteoporos.Int. 11, 59-67.
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Trained Athletes. Int.J Sports Med.
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11 APPENDIX – Publications related to the VBR-Study
112
a) Congress Abstracts
Liphardt AM, Jansen C, Kleinöder H, Heer M, Mester J (2007): The potential of
whole body vibration training during 14-days of 6°-head down tilt bed rest to affect
balance. 4th European Congress: Medicine in Space and extreme Environments,
Berlin, Germany
Zange J, Liphardt AM, Schmidt A, Müller K, Kleinöder H, Heer M, Mester J (2006):
20-Hz whole body vibration training fails to counteract the decrease in leg muscle
performance and volume induced by 14 days of 6° head down tilt bed rest. 8th
Congress of Medicine and Mobility, Berlin, Germany.
Baecker N, Liphardt AM, Frings P, Heer M (2006): Effects of vibration training on
bone metabolism in immobilized healthy subjects. 8th Congress of Medicine and
Mobility, Berlin, Germany.
Liphardt AM, Bäcker N, Mündermann A, Koo S, Andriacchi T, Zange J, Mester J,
Heer M (2006): The potential of vibration training to affect the response of muscle,
bone and cartilage during short term bed rest.
15th World Congress of
Biomechanics, Munich, Germany.
Liphardt AM, Mündermann A, Koo S, Bäcker N, Andriacchi T, Zange J, Mester J,
Heer M (2006): Changes in Cartilage Morphology of the Knee after 14-days of Bed
Rest. 36th COSPAR Scientific Assembly, Beijing, China.
Liphardt AM, Adams F, Gottschalk S, Bäcker N, Frings P, Heer M, Luft FC2,
Jordan J, Boschmann M (2006): Impact of daily whole body vibration training (WVT)
on muscle blood flow and metabolism during 14 days of bed rest. 11th Annual
Congress of the European College of Sport Science, Lausanne, Switzerland.
Liphardt AM, Zange J, Schmidt A, Kleinöder H, Heer M, Mester J (2006): 20-Hz
Whole body vibration training fails to counteract negative effects of 14 days of bed
rest on muscle performance. 11th Annual Congress of the European College of
Sport Science, Lausanne, Switzerland.
113
Zange J, Liphardt AM, Müller K, Mester J (2006): 20Hz whole body vibration
training fails to counteract the decrease in leg muscle volume induced by 14 days of
6° head down tilt bed rest. 11th Annual Congress of the European College of Sport
Science, Lausanne, Switzerland.
Liphardt AM, Mündermann A, Bäcker N, Zange J, Mester J, Heer M (2006): Serum
COMP concentration is sensitive to a 14.day bedr rest intervention. 52nd Annual
Meeting of the Orthopaedic Research Society, Chicago, Illinois, USA.
Bäcker N, Liphardt AM, Frings P, Boese A, Heer M (2005): Effects of mechanical
stimuli via vibration plate training on bone metabolism in immobilized healthy
subjects. 56th International Astronautical Congress, Fukuoka, Japan.
Liphardt AM, Mündermann A, Koo S, Zange J, Mester J, Heer M (2005): The Effect
of Vibration Training During 14-Day Bed-Rest on Articular Cartilage Morphology.
European Space Agency (ESA) and International Society of Gravitational
Physiology (ISGP) Joint Life Science Conference, Cologne, Germany.
Zervoulakos P, Blank C, May F, Gauger P, Liphardt AM, Heer M, Beck L (2005):
Vibration training fails to improve orthostatic tolerance after 14 days of 6° HDT bed
rest. European Space Agency (ESA) and International Society of Gravitational
Physiology (ISGP) Joint Life Science Conference, Cologne, Germany.
12 Danksagung
114
12 Danksagung
Ich bedanke mich herzlich bei allen Personen, die mich bei der Erstellung dieser
Arbeit unterstützt und begleitet haben. Mein besonderer Dank gilt:
Prof. Dr. Dr. h.c. mult. Joachim Mester für die Überlassung des Themas sowie die
fachliche Diskussion und die ständige Bereitschaft mich zu unterstützen.
Frau PD. Dr. Martina Heer für die Möglichkeit diese Studie in ihrer Abteilung
(Weltraumphysiologie, DLR-Institut für Luft- und Raumfahrtmedizin) durchführen zu
dürfen. Auch für die zahlreichen, intensiven wissenschaftlichen Diskussionen, in
denen ich unendlich gelernt habe und die mich in meinem Tun immer bestärkt
haben, danke ich ihr von Herzen. Sie hat mich zu jeder Zeit voll unterstützt und es
mir ermöglicht die Ergebnisse meiner Arbeit auch auf nationalen und internationalen
wissenschaftlichen Kongressen zu präsentieren. Herzlichen Dank dafür!
Frau Dr. Natalie Bäcker für die hervorragende Betreuung, die vielen Gespräche,
sowie für die organisatorische und wissenschaftliche Unterstützung bei der
Durchführung der VBR-Studie. Ihre Erfahrungen und Kenntnisse waren eine sehr
wertvolle Hilfe und unerlässlich für den erfolgreichen Abschluss meiner Dissertation.
PD Dr. Jochen Zange für seine Unterstützung und die wissenschaftliche Diskussion
bei der Fertigstellung der Arbeit.
Frau Dr. Petra Frings-Meuthen für die vielen Diskussionen und hilfreichen
Kommentare.
Meinen Probanden für ihre Kooperationsbereitschaft und ihr großes Engagement
bei allen Experimenten.
Prof. Dr. James Wakeling, Simon Fraser University, Vancouver, Kanada, und Dr.
Annegret Mündermann, University of Otago, Dunedin, Neuseeland, für das Lesen
des Manuskripts, die wissenschaftlichen Diskussionen und die unermüdliche
Unterstützung.
Prof. Dr. Thomas P. Andriacchi, Stanford University, Stanford, USA,
für die
freundliche Aufnahme als Gaststudent in seinem Team und die Unterstützung bei
der Auswertung der Knorpeldaten.
Dr. Seungbum Koo, Stanford University, Stanford, USA, für die wissenschaftliche
Diskussion und Hilfe bei der Auswertung und Interpretation der Knorpeldaten.
Dr. Michael Boschmann, Charité Berlin, für das Lesen der Arbeit und seine
Bereitschaft als Mitglied der Prüfungskommission zu Verfügung zu stehen.
Frau Dr. Francisca May und Herrn Christoph Blank für ihren unermüdliche Einsatz
bei der medizinischen Betreuung unserer Probanden.
12 Danksagung
115
Frau Gabriele Kraus und Frau Jette Hjorth-Müller für ihre Hilfe bei der analytischen
Auswertung im Labor.
Herrn Henning Soll und Frau Heidi Bonnist
für die sehr erfolgreiche
Zusammenarbeit bei der psychologischen Auswahl der Probanden, sowie Herrn
Paul Kuklinski und Herrn Götz Kluge und Team für die Unterstützung bei der
medizinischen Auswahl der Probanden.
Den Mitarbeiterinnen und Mitarbeitern des Instituts für Trainingswissenschaft und
Sportinformatik, DSHS Köln, für ihre Unterstützung bei der Planung und
Durchführung der Kraftleistungsdiagnostik, insbesondere den beiden ehemaligen
Diplomanden Christiane Jansen und Axel Schmidt.
Den Mitarbeitern der Abteilung Weltraumphysiologie, DLR-Institut für Luft- und
Raumfahrtmedizin,
für
ihren
unermüdlichen
Arbeitseinsatz
sowie
die
freundschaftliche Zusammenarbeit und Arbeitsatmosphäre. Der Zusammenhalt und
die ständige Unterstützungsbereitschaft auch in arbeitsintensiven Zeiten haben mich
sehr beeindruckt. Ohne ihren Einsatz wäre die Durchführung der VBR-Studie nicht
möglich gewesen.
Herrn Roy McLean für das Lesen und Korrigieren des Manuskripts als
Muttersprachler.
Dem DLR sowie dem Deutschen Akademischen Austauschdienst und der
‚International Society of Biomechanics’ für die finanzielle Unterstützung.
Meinen Eltern für ihre Liebe und die immerwährende Unterstützung und Bestärkung
in meinem Tun.
Meinem Mann Jan und unserer Tochter Mia-Elisa für ihre Liebe, Geduld und
Unterstützung.
13 Curriculum Vitae
116
13 Curriculum Vitae
Name:
Anna-Maria Liphardt, Dipl. Sport Scientist
Date of birth:
02.02.1978
Place of birth:
Eschwege, Hessen, Germany
Parents:
Dieter Liphardt g
Edith Liphardt geb. Escher
Family status:
married, one child
EDUCATION
2003 / Jun
– present
PhD student
German Sport University Cologne, Köln, Germany
1998 /Oct
2003 / May
Sport Science (Diploma)
German Sport University Cologne, Köln, Germany
Thesis Title: Soft Tissue Vibrations of the Lower Extremity during
Walking
1998 / Oct
2003 / Dec
Biological Education (Staatsexamen)
Universität Köln, Cologne, Germany
1997 / Jun
Allgemeine Hochschulreife (Abitur)
Herderschule Kassel, Germany
PROFESSIONAL EXPERIENCE
2007 / May
- present
Research Assistant,
Institute of Training Science and Sport Informatics, German
Sports University Cologne (DSHS), Köln, Germany (part time)
2007 / June
- present
Research Assistant, Institute of Aerospace Medicine
German Aerospace Center, Köln, Germany (part time)
2007/ April
- present
Assistant lecturer
Seminar: Modern insight of training with children and
adolescents. German Sport University (DSHS) Cologne,
Cologne, Germany
2006 / Aug
- 2007 / April
Maternity leave
2003 / Jun
– 2006 / Aug
Ph.D. Candidate, Institute of Aerospace Medicine
German Aerospace Center, Cologne, Germany
Project: ‘Vibration as a countermeasure for the physiological
effects of space flight’
Supervisor: PD Dr. Martina Heer, Prof. Dr. Joachim Mester
13 Curriculum Vitae
117
2005 / May
Visiting Student, Biomotion Laboratory
Stanford University, Palo Alto, USA
Project: ‘The effect of vibration training during immobilization on
knee cartilage’
Supervisor: Dr. Anne Mündermann, Dr. Tom Andriacci
2004 / Oct
– 2004 / Nov
Visiting Student, Biomotion Laboratory
Stanford University, Palo Alto, USA
Project: ‘The effect of vibration training during immobilization on
knee cartilage’
Supervisor: Dr. Anne Mündermann, Prof. Dr. Tom Andriacci
2002 / Aug
– 2003 / Jan
Visiting Student, Human Performance Laboratoy
University of Calgary, Canada
Project: ‘Soft Tissue Vibrations of the Lower Extremity During
Walking’
Supervisor: Dr. James Wakeling, Prof. Dr. Benno Nigg
2000 – 2003
Student Research Assistant, Department of Individual Sports
German Sport University Cologne, Germany
Specialization: Gymnastics
AWARDS AND SCHOLARSHIPS
2006 Young Investigator Award of the German Sports University Cologne,
Germany
2005 Young Investigator Award at the European Space Agency (ESA) and
International Society of Gravitational Physiology (ISGP) ‘Joint Life Science
Conference’, 2nd Place
2005 European Space Agency, Young Investigator Travel Sponsorship
2005 ISB Travel Grant, International Society of Biomechanics
2004 Travel Grant, Deutscher Akademische Austausch Dienst (DAAD), Germany
2003
Young Investigator Award of the European College of Sport Science, Finalist
2002
“Study Abroad Award”, full competitive scholarship, Deutscher Akademischer
Austausch Dients (DAAD), Germany
PUBLICATIONS
JOURNALS
Wakeling JM, Liphardt AM (2005). Task specific recruitment of motor units for vibration
damping. Journal of Biomechanics, J Biomech. 2006;39(7):1342-6.
Wakeling JM, Liphardt AM, Nigg BM (2003). Muscle activity reduces soft-tissue resonance
at heel-strike during walking. Journal of Biomechanics 36, 1761 – 1769
13 Curriculum Vitae
118
PEER-REVIEWED ABSTRACTS
Liphardt AM, Jansen C, Kleinöder H, Heer M, Mester J (2007): The potential of whole body
vibration training during 14-days of 6°-head down tilt bed rest to affect balance. 4th
European Congress: Medicine in Space and extreme Environments, Berlin, Germany
Zange J, Liphardt AM, Schmidt A, Müller K, Kleinöder H, Heer M, Mester J (2006): 20-Hz
whole body vibration training fails to counteract the decrease in leg muscle performance and
volume induced by 14 days of 6° head down tilt bed rest. 8th Congress of Medicine and
Mobility, Berlin, Germany.
Bargmann A, Liphardt AM, Rosenberger A, Zange J, Beck L (2006): Effects of vibration
training on the cardiovascular system (Pilot-Vibration-Training Study). 8th Congress of
Medicine and Mobility, Berlin, Germany.
Baecker N, Liphardt AM, Frings P, Heer M (2006): Effects of vibration training on bone
metabolism in immobilized healthy subjects. 8th Congress of Medicine and Mobility, Berlin,
Germany.
Rosenberger A, Liphardt AM, Bargmann A, Müller K, Zange J, Mester J (2006): Effects of
vibration training and resistive exercise on fatigability of leg muscles (Pilot-Vibration-Study).
8th Congress of Medicine and Mobility, Berlin, Germany.
Liphardt AM, Bäcker N, Mündermann A, Koo S, Andriacchi T, Zange J, Mester J, Heer M
(2006): The potential of vibration training to affect the response of muscle, bone and
cartilage during short term bed rest.
15th World Congress of Biomechanics, Munich,
Germany.
Liphardt AM, Mündermann A, Koo S, Bäcker N, Andriacchi T, Zange J, Mester J, Heer M
(2006): Changes in Cartilage Morphology of the Knee after 14-days of Bed Rest. 36th
COSPAR Scientific Assembly, Beijing, China.
Liphardt AM, Adams F, Gottschalk S, Bäcker N, Frings P, Heer M, Luft FC2, Jordan J,
Boschmann M (2006): Impact of daily whole body vibration training (WVT) on muscle blood
flow and metabolism during 14 days of bed rest. 11th Annual Congress of the European
College of Sport Science, Lausanne, Switzerland.
Liphardt AM, Zange J, Schmidt A, Kleinöder H, Heer M, Mester J (2006): 20-Hz Whole body
vibration training fails to counteract negative effects of 14 days of bed rest on muscle
performance. 11th Annual Congress of the European College of Sport Science, Lausanne,
Switzerland.
Zange J, Liphardt AM, Müller K, Mester J (2006): 20Hz whole body vibration training fails to
counteract the decrease in leg muscle volume induced by 14 days of 6° head down tilt bed
13 Curriculum Vitae
119
rest. 11th Annual Congress of the European College of Sport Science, Lausanne,
Switzerland.
Liphardt AM, Mündermann A, Bäcker N, Zange J, Mester J, Heer M (2006): Serum COMP
concentration is sensitive to a 14.day bedr rest intervention. 52nd Annual Meeting of the
Orthopaedic Research Society, Chicago, Illinois, USA.
Bäcker N, Liphardt AM, Frings P, Boese A, Heer M (2005): Effects of mechanical stimuli via
vibration plate training on bone metabolism in immobilized healthy subjects. 56th
International Astronautical Congress, Fukuoka, Japan.
Liphardt AM, Mündermann A, Koo S, Zange J, Mester J, Heer M (2005): The Effect of
Vibration Training During 14-Day Bed-Rest on Articular Cartilage Morphology. European
Space Agency (ESA) and International Society of Gravitational Physiology (ISGP) Joint Life
Science Conference, Cologne, Germany.
Zervoulakos P, Blank C, May F, Gauger P, Liphardt AM, Heer M, Beck L (2005): Vibration
training fails to improve orthostatic tolerance after 14 days of 6° HDT bed rest. European
Space Agency (ESA) and International Society of Gravitational Physiology (ISGP) Joint Life
Science Conference, Cologne, Germany.
Liphardt AM, Wakeling JM, Nigg BM, Mester J (2004): Potential of vibration training for the
maintenance of muscle performance during spaceflight. 25th Annual International
Gravitational Physiology Meeting, Russian Academy of Sciences, Moscow, Russia.
Liphardt AM, Wakeling JM (2004): Functional recruitment of muscle during vibration
damping. 9th Annual Congress of the European College of Sport Science, ClairmontFerrand, France.
Liphardt AM (2003): Vibration Training as a countermeasure against the effects of
microgravity on bone and skeletal muscle. 1st Space Medicine Workshop for Students,
European Astronaut Centre, Cologne, Germany.
Liphardt AM, Wakeling JM, Nigg BM, Mester J. (2003). Effect of different shoe hardnesses
on EMG intensity and soft tissue vibrations of the lower extremity during walking. 8th Annual
Congress of the European College of Sport Science, Salzburg, Austria.
Köln, den 30.01.2008
___________________________________________________________________

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