1 STEP-EXERCISE MAY BE INCLUDED IN BONE HEALTH

1
STEP-EXERCISE MAY BE INCLUDED IN BONE HEALTH PROMOTION
PROGRAMS
Rita Santos-Rocha1,2, Maria Lourdes Machado2, António Veloso2
1Sport Sciences School of Rio Maior, Polytechnic Institute of Santarém, Portugal
2Laboratory of Biomechanics, Faculty of Human Kinetics, Technical University of
Lisbon, Portugal
Running title
STEP-EXERCISE AND BONE HEALTH
To the Editor of the Women in Sport and Physical Activity Journal:
The present paper untitled “STEP-EXERCISE MAY BE INCLUDED IN BONE
HEALTH PROMOTION PROGRAMS”, by Rita Santos-Rocha, Maria Lourdes
Machado and António Veloso, has not been published in another journal, is not under
consideration elsewhere, and will not be submitted elsewhere before a final editorial
decision from Women in Sport and Physical Activity Journal is rendered.
Rita Santos-Rocha
Date of submission: October 8, 2007
2
Corresponding author: Rita Santos-Rocha
Affiliation: Sport Sciences School of Rio Maior, Polytechnic Institute of Santarém,
Portugal (www.esdrm.pt); Laboratory of Biomechanics, Faculty of Human Kinetics,
Technical University of Lisbon, Portugal (www.fmh.utl.pt)
Mailing address: Urb Jardins da Parede, Av das Tilias, 104-1A, 2775-335 Parede,
Portugal
E-mail address: [email protected]
Other e-mail addresses: [email protected]; [email protected]
Phone number: +351-966036856; +351-964824089; Fax: +351-243999282
Brief informational note of activities:
Employment: Classes of Assessment and Exercise Prescription, Physical Activity
and Public Health, and Biomechanics of Sports - Department of Fitness & Health,
Sport Sciences School of Rio Maior, Polytechnic Institute of Santarém, Portugal
(www.esdrm.pt). Vice-President of Sport Sciences School of Rio Maior. Researcher
at the Laboratory of Biomechanics, Faculty of Human Kinetics, Technical University
of Lisbon, Portugal (www.fmh.utl.pt).
Degrees: BSc (Sport Sciences), MSc (Exercise & Health). PhD (Health & Fitness Biomechanics).
Research interests: Sports Biomechanics, Exercise & Health, bone health,
pregnancy.
3
2nd author: Maria Lourdes Machado
Affiliation: Laboratory of Biomechanics, Faculty of Human Kinetics, Technical
University of Lisbon, Portugal (www.fmh.utl.pt); E-mail address:
[email protected]; Phone number: +351-967097555
Brief informational note of activities:
Employment: PhD student at the Laboratory of Biomechanics, Faculty of Human
Kinetics, Technical University of Lisbon, Portugal.
Degrees: BSc (Physical Education), MSc (Exercise & Health)
Research interests: Sports Biomechanics, Exercise & Health, elderly.
3rd author: António Veloso
Affiliation: Laboratory of Biomechanics, Faculty of Human Kinetics, Technical
University of Lisbon, Portugal (www.fmh.utl.pt); Mailing address: Faculdade de
Motricidade Humana, Estrada da Costa, 1495-699 Cruz Quebrada, Portugal; E-mail
address: [email protected]; Phone number: +351-966485286
Brief informational note of activities:
Employment: Classes of Biomechanics of Sports. Vice-President of the Faculty of
Human Kinetics, Associate Professor and Head of the Laboratory of Biomechanics,
Faculty of Human Kinetics, Technical University of Lisbon, Portugal (www.fmh.utl.pt).
Degrees: BSc (Physical Education), PhD (Sport Biomechanics).
Research interests: Sports Biomechanics, Ergonomics, Exercise & Health.
4
Prior accomplishments of authors:
Articles in journals
Santos-Rocha, R; Brandão, F; Cipriano, H; Asseiceiro, C & Veloso, A (2003). Prevalência de Perturbações
Músculo-Esqueléticas em Instrutores de Fitness. Estudo Exploratório. Desporto, Investigação & Ciência –
Revista Científica da Escola Superior de Desporto de Rio Maior, n.º 3. Rio Maior: ESDRM (pp 89-106).
(portuguese journal)
Santos-Rocha, R; Pezarat-Correia, P; Franco, S & Veloso, A (2004). Análise da Participação Muscular no Passo
Básico de Step: Efeito da Velocidade da Música e da Altura da Plataforma. Revista Brasileira de
Biomecânica – Brazilian Journal of Biomechanics, Ano 5, Número 8, Maio 2004 São Paulo: Estação
Liberdade(pp 5-12).(in portuguese)
Santos-Rocha, R; Oliveira, C & Veloso, A (2006). Osteogenic Index of Step Exercise Depending on
Choreographic Movements, Session Duration and Stepping Rate. British Journal of Sports Medicine,
40:860–866 (published online 18 Aug 2006 (DOI: 10.1136/bjsm.2006.029413).
Santos-Rocha, R & Veloso, A (2007). Comparative Study of Plantar Pressure During Step Exercise in Different
Floor Conditions. Journal of Applied Biomechanics, Vol 23: 158-164.
Submitted:
Santos-Rocha, R., Veloso, A., Valamatos, M.J., Machado, M.L. and André, H.I.. (2007). Analysis of kinematics of
the lower limb during step-exercise. Submitted to Research in Sports Medicine.
Santos-Rocha, R., Veloso, A., Machado, M.L., Valamatos, M.J. and Ferreira, C. (2007). Peak ground and joint
reaction forces in step-exercise depending on step-pattern and stepping-rate. Submitted to Research in
Sports Medicine.
Santos-Rocha, R., Veloso, A. and Machado, M.L. (2007). Analysis of ground reaction forces in step-exercise
depending on step-pattern and stepping-rate. Submitted to Journal of Strength and Conditioning
Research.
Santos-Rocha, R., Veloso, A., Machado, M.L., Valamatos, M.J. and Ferreira, C. (2007) Effect of stepping-rate and
step-pattern on the kinetics and kinematics of lower limb during step-exercise. Submitted to Journal of
Applied Biomechanics
International congresses
Pezarat-Correia, P; Franco, S.; Santos, R & Veloso, A (1999). Caracterização da Participação Muscular na
Actividade de Step. VII Congresso de Educação Física e Ciências do Desporto dos Países de Língua
Portuguesa, Agosto 1999,. Florianópolis: UFSC e EDESC, Brasil. (pp 268) (in Portuguese)
Santos, R; Franco, S; Pezarat-Correia, P & Veloso, A (2000). Influence of Music Tempo on Muscle Participation
Pattern in Step Exercise. In Avela, J; Komi, PV & Komulainen, J (Eds), Proceedings of the 5th Annual
Congress European College of Sport Science, July 19-23, Jyvaskyla, Finland (pp 644).
Franco, S; Santos, R; Pezarat-Correia, P & Veloso, A (2000). Influence of Bench Height on Muscle Participation
Pattern in Step Exercise. In Avela, J; Komi, PV & Komulainen, J (Eds), Proceedings of the 5th Annual
Congress European College of Sport Science, July 19-23, Jyvaskyla, Finland (pp 269).
Santos-Rocha, R; Franco, S; Pezarat-Correia, P & Veloso, A (2000). Influência da Cadência da Música na
Participação Muscular no Exercício de Step. Livro de resumos do VIII Congresso de Educação Física e
Ciências do Desporto dos Países de Língua Portuguesa - Faculdade de Motricidade Humana, Dezembro,
13-17, Lisboa, Portugal (pp 83). (in Portuguese)
5
Franco, S; Santos-Rocha, R; Pezarat-Correia, P & Veloso, A (2000). Influência da Altura da Plataforma na
Participação Muscular no Exercício de Step. Livro de resumos do VIII Congresso de Educação Física e
Ciências do Desporto dos Países de Língua Portuguesa - Faculdade de Motricidade Humana, Dezembro,
13-17, Lisboa, Portugal (pp 43).
Santos-Rocha, R; Veloso, A; Franco, S & Pezarat-Correia, P (2001). Biodinamics of Step Down Phase of Step
Exercise. Influence of Music Speed. Medicine & Science in Sports & Exercise, Volume 33:5 Supplement 48th Annual Meeting of the American College of Sports Medicine, May 30-June 2, Baltimore, Maryland,
USA (pp 400).
Santos-Rocha, R; Veloso, A; Franco, S & Pezarat-Correia, P (2001). Biodinamics of Step Down Phase of Step
Exercise. Influence of Bench Height. In Mester, J; King, G; Strüder, H; Tsolakidis, E & Osterburg, A (Eds),
Proceedings of the 6th Annual Congress European College of Sport Science, July 24-28, Cologne,
Germany (pp 801).
Santos-Rocha, R; Veloso, A; Santos, H; Franco, S & Pezarat-Correia, P (2002). Ground Reaction Forces of Step
Exercise Depending on Step Frequency and Bench Height. In Gianikellis, KE (Ed), Scientific Proceedings
of the XXth International Symposium on Biomechanics in Sports – International Society of Biomechanics in
Sports, July 1-5, Cáceres, Spain (pp 156-8).
Santos-Rocha, R; Brandão, F; Asseisseiro, C; Cipriano, H & Veloso, A (2002). Prevalence of Musculoskeletal
Disorders in Fitness Instructors. In Koskolou, M; Geladas, N & Klissouras, V (Eds), Proceedings of the 7th
Annual Congress of the European College of Sport Science, July 24-28, Athens, Greece (pp 527).
Santos-Rocha, R & Veloso, A (2003). Modelling Exercise for Health. In Müller, E; Schwameder, H; Zallinger, G &
Fastenbauer, V (Eds), Proceedings of the 8th Annual Congress of the European College of Sport Science,
July 8-13,Salzburg, Austria (pp 232 and CD).
Santos-Rocha, R & Veloso, A (2004). Joint Reaction Forces and Moments of Step Exercise. In van Praagh, E;
Coudert, J; Fellmann, N & Duché, P (Eds), Book of Abstracts of the 9th Annual Congress of the European
College of Sport Science, July 3-6, Clermont-Ferrand, France (pp 340 and CD).
Aguiar, L; Santos-Rocha, R & Veloso, A (2004). Estudo de Caso sobre Determinação por Dinâmica Inversa da
Carga Mecânica na Fase de Recepção do Exercício de Step. Revista Portuguesa de Ciências do
Desporto, volume 4, n.º 2, Setembro 2004 (pp 292), suplemento - X Congresso de Ciências do Desporto e
de Educação Física dos Países de Língua Portuguesa, Set 27-Out 1, Porto, Portugal. (in Portuguese)
Pedro, A & Santos-Rocha, R (2004). Análise das Estratégias de Prescrição do Exercício na Gravidez na
Perspectiva do Professor e da Praticante. Revista Portuguesa de Ciências do Desporto, volume 4, n.º 2,
Setembro 2004 (pp 320), suplemento - X Congresso de Ciências do Desporto e de Educação Física dos
Países de Língua Portuguesa, Set 27-Out 1, Porto, Portugal. (in Portuguese)
Cardoso, AL; Santos-Rocha, R & Raposo, P (2004). Caracterização dos Factores de Saúde e Segurança no
Trabalho, em Ginásios da Grande Lisboa. Revista Portuguesa de Ciências do Desporto, volume 4, n.º 2,
Setembro 2004 (pp 342), suplemento - X Congresso de Ciências do Desporto e de Educação Física dos
Países de Língua Portuguesa, Set 27-Out 1, Porto, Portugal. (in Portuguese)
Santos-Rocha, R & Veloso, A (2004). Sports Biomechanics – Kinetic Analysis of Exercise Using Inverse
Dynamics and Pressure Insoles. In B.H.V. Topping & C.A. Mota Soares (eds.) Publicação em cd e
Proceedings of the 7th International Conference on Computational Structures Technology, Sept 7-9,
Lisbon, Portugal (pp 205-206).
Santos-Rocha, R; Machado, ML; André, HI; Mira, P & Veloso, A (2005). Plantar Pressure and Peak Vertical
Ground Reaction Forces in Step Exercise (Knee Lift). Influence of Music Speed. In Dikic, N; Zivanic, S;
Ostojic, S; Tornjanski, Z (Eds), Abstract book of the 10th Annual Congress of the European College of
Sport Science, July 13-16, Belgrade, Serbia (pp 190).
6
Machado, ML; André, H; Santos-Rocha, R; Veloso, A & Carnide, F (2005). Can Step Exercise Prevent Gait
Impairments in Elderly Women? A Kinetic Analysis. In Wang, Q (Ed), Proceedings of the XXIII
International Symposium on Biomechanics in Sports (2 volumes), The China Institute of Sport Science,
August 22-27, Beijing, China (pp 664-667).
Santos-Rocha, R & Veloso, A (2005). Plantar Pressure and Peak Ground Reaction Forces in Step Exercise.
Comparison of Field and Laboratory Assessment. In Rodrigues, H; Cerrolaza, M; Doblaré, M; Ambrósio, J
& Viceconti, M (Eds), Proceedings of the ICCB 2005 – II International Conference on Computational
Bioengineering (volumes 1 & 2), Set 14-16, Lisbon, Portugal (pp 885-894).
André, HI; Machado, ML; Veloso, AP; Carnide, MF & Santos-Rocha, R (2005). Análise Biomecânica da
Locomoção de Mulheres Idosas Activas em Planos Desnivelados de Deslocamento. Congresso Brasileiro
de Biomecânica. Agosto, Brasil. (in Portuguese)
Machado, M; Moreira, H; Santos-Rocha, R; André, HI & Veloso, A (2006). Step Senior Exercise Program
Promotes Functionality. 53rd Annual Meeting of the American College of Sports Medicine, May 31-June 3,
Denver, USA. (pp 290)
Santos-Rocha, R; Oliveira, C & Veloso, A (2006). Osteogenic Index of Step Exercise. In 11th Congress of the
European College of Sports Science, July 5-8, Lausanne, Switzerland. (pp 200)
Machado, M; Santos-Rocha, R & Veloso, A (2006). Impulse and Average Ground Reaction Force in Step
Exercise. International Society of Biomechanics in Sports, August 5-8, Salzburg, Austria. (pp 190)
Machado, M; Santos-Rocha, R & Veloso, A (2006). Peak Vertical Ground Reaction Force in Step Exercise. In 11th
Congress of the European College of Sports Science, July 5-8, Lausanne, Switzerland. (pp 200)
Santos-Rocha, R; Veloso, A; Machado, ML; Ferreira, C & Valamatos, MJ (2007). Peak ground and joint reaction
forces in the lower limb in step exercise depending on step pattern and stepping rate. In Kallio, J; Komi, P;
Komulainen, J; Avela, J (Eds), Abstract book of the 12th Annual Congress of the European College of
Sport Science, July 11-14, Jyvaskyla, Finland (pp 165).
Machado, ML; Santos-Rocha, R; Veloso, A (2007). Mechanical Load in step exercise. In Kallio, J; Komi, P;
Komulainen, J; Avela, J (Eds), Abstract book of the 12th Annual Congress of the European College of
Sport Science, July 11-14, Jyvaskyla, Finland (pp 183).
Filipa, J; Moniz_Pereira, V; Veloso, A (2007). Does exercise allow elderly people to retain the dynamics of gait?.
In Kallio, J; Komi, P; Komulainen, J; Avela, J (Eds), Abstract book of the 12th Annual Congress of the
European College of Sport Science, July 11-14, Jyvaskyla, Finland (pp 445).
Moniz_Pereira, V; Filipa, J; Veloso, A (2007). Effects of exercise in gait kinematics in elderly men. In Kallio, J;
Komi, P; Komulainen, J; Avela, J (Eds), Abstract book of the 12th Annual Congress of the European
College of Sport Science, July 11-14, Jyvaskyla, Finland (pp 581).
7
1 STEP-EXERCISE MAY BE INCLUDED IN BONE HEALTH PROMOTION
2 PROGRAMS
3
4 Abstract
5 Physical exercise has been found to be effective in the prevention of osteoporosis,
6 especially those activities that include impact loading. Activities such as walking,
7 jogging and stair climbing, introduce stress to the skeleton through ground reaction
8 forces (GRF). The analysis of GRF help to understand the magnitude and pattern of
9 loading experienced by the body while in contact with the ground. Our purposes were
10 to analyze the peak-GRF and loading-rate produced by Step-Exercise in 18 skilled
11 females; and to investigate the effect of stepping-rate and step-pattern. Step12 Exercise seems to produce greater loading than walking and at increased stepping13
rates its loading could be compared to those obtained during comfortable running.
14 The results indicated that loading can be effectively controlled by varying stepping15
rate and step-patterns during classes, and how experienced subjects deal with the
16 increase of external load. Controlled stepping exercise appears relatively safe with
17 respect to the magnitude of loading.
18
19 Key words: exercise and health, peak ground reaction forces, repeated measures.
20
21
8
22 INTRODUCTION
23 Recreational Exercise aiming to improve or maintain health and fitness constitutes a
24 group of physical activities performed by a large number of participants worldwide,
25 regardless of age and physical or health status. The main objectives of these
26 physical activities are to provide healthy mechanical and metabolic stimuli as well as
27 fun. Besides its cardiovascular benefits, the organization of exercise sessions and
28 exercise prescription, concerning rate and magnitude of skeletal loading, can
29 improve the osteogenic potential of physical activity (Cullen et al., 2001; Turner &
30 Robling, 2003).
31 Exercise Prescription concerns in a sequence of procedures aiming to adapt
32 the stimuli of the different forms and modes of Exercise to participant’s goals and
33 needs, using the information of health and fitness assessment, respecting the main
34 roles of Exercise and the safety of participants.
35 In what is concerned to health-related cardiovascular Exercise, plenty of well
36 documented references can be found in literature. Those include the metabolic
37 expenditure of several forms of physical activity (ACSM, 2005) and the step-by-step
38 case studies developed in order to adapt the metabolic calculations to meet
39 participants’ goals of losing weight or improving cardiorespiratory fitness. To give a
40 figurative example, considering that a person is running for 30 min at a comfortable
41 speed, this kind of exercise could be considered a stimulus that can be translated in
42 a “aerobic effort whose intensity is about 60% of the maximal oxygen uptake, which
43 is consuming a certain amount of calories”, or in a “mechanical effort of which vertical
44 component of the ground reaction force is about 1600 Newton or about two times the
45 person’s body weight and it has been applied around 1500 times on each feet”. In the
46 first case, we are referring to the specific benefits of this exercise on the
9
47 cardiorespiratory and immunitary systems and to the effects in body composition and
48 cardiovascular health. In the second case, we are referring to the specific benefits of
49 this exercise on the musculoskeletal system and to the effects in body composition
50 and bone health.
51 Bone mineral density, osteoporosis and osteoporotic fractures have become
52 one of the major health problems in Western countries (Cummings & Melton, 2002).
53 Osteoporosis is a disease characterized by low bone mass and microarchitectural
54 deterioration of bone tissue leading to enhanced bone fragility and a consequent
55 increase in fracture risk (ACSM, 1995). As osteoporosis is more common in females,
56 more exercise-related research has been directed at reducing the risk of osteoporotic
57 fractures in women. Factors that influence fracture risk include skeletal fragility,
58 frequency and severity of falls, and tissue mass surrounding the skeleton. Prevention
59 of osteoporotic fractures, therefore, is focused on the preservation or enhancement
60 of the material and structural properties of bone, the prevention of falls, and the
61 overall improvement of lean tissue mass (ACSM, 1995). Normal physiological loading
62 causes a range of deformation reactions (strains) in bone, including compression,
63 tension, shear, torsion, and vibration. Bone exhibits an intrinsic ability to adapt to
64 alterations in chronic loading to withstand future loads of the same nature (Wolff’s
65 Law). Adaptation of bone to load changes occurs via increased modeling and/or
66 remodeling. Modeling is a process whereby bone tissue is either deposited or
67 removed to modify the shape and size of a bone. Remodeling describes a process of
68 bone resorption, followed (after a delay of roughly one month) by deposition of new
69 bone (for approximately six months). While some level of remodeling is constantly
70 occurring in normal bone, in bone undergoing adaptation to altered loading, the
71 degree of remodeling increases substantially. The initial increase in resorption will
10
72 render a bone relatively porous until the process of deposition can fully replace the
73 lost tissue. During this prolonged replacement phase, bone is more susceptible to
74 stress fracture by virtue of increased porosity (Beck, 2000).
75 Physical exercise has been found to be effective in the prevention of
76 osteoporosis, especially those activities that include impact loading (ACSM, 1995;
77 Layne & Nelson, 1999; Wallace & Cumming, 2000; Witzke & Snow, 2000; Bauer et
78 al., 2001; Nikander et al., 2005; Jämsä et al., 2006). Physical activity, particularly
79 weight-bearing exercise, is thought to provide the mechanical stimuli or "loading"
80 important for the maintenance and improvement of bone health, whereas physical
81 inactivity has been implicated in bone loss and its associated health costs. Also,
82 high-intensity resistance training, in contrast to traditional pharmacological and
83 nutritional approaches for improving bone health in older adults, has the added
84 benefit of influencing multiple risk factors for osteoporosis including improved
85 strength and balance and increased muscle mass (Layne & Nelson, 1999). The cross
86 sectional study of Yung et al. (2005) indicated that regular participation in weight
87 bearing exercise in young people (18-22 years) might be beneficial for accruing peak
88 bone mass and optimizing bone structure. The load-bearing capacity of bone reflects
89 both its material properties, such as density and modulus, and the spatial distribution
90 of bone tissue. These features of bone strength are all developed and maintained in
91 part by forces applied to bone during daily activities and exercise. Functional loading
92 through physical activity exerts a positive influence on bone mass in humans. The
93 extent of this influence and the types of programs that induce the most effective
94 osteogenic stimulus are still uncertain. While it is well-established that a marked
95 decrease in physical activity, as in bed rest for example, results in a profound decline
96 in bone mass, improvements in bone mass resulting from increased physical activity
11
97 are less conclusive (ACSM, 1995). Kohrt et al. (1997) defined that activities such as
98 walking, jogging and stair climbing, constitute a group of exercises that introduce
99 stress to the skeleton through ground reaction forces (GRF); and activities such as
100 weight lifting and rowing constitute a group of exercises that introduce stress to the
101 skeleton through joint reaction forces (JRF). Both the GRF and the JRF exercise
102 programs resulted in significant and similar increases in BMD of the whole body.
103 Nikander et al. (2005) performed a research with 255 premenopausal female athletes
104 and referred that the loadings that arise from high impacts or impacts from atypical
105 loading directions seem to be effective. Also, the authors reported that high-impact
106 loading (e.g. volleyball) and odd-impact loading (e.g. step aerobics and soccer)
107 activities were associated with the highest body mineral density (BMD) of the femoral
108 neck and bone strength (index Z) when compared to high-magnitude loading (e.g.
109 weightlifting), low-impact loading (e.g. orienteering and cross-country skiing), and
110 non-impact loading (e.g. swimming and cycling) activities. A recent publication
111 studied for the first time the association between the intensity of physical activity and
112 proximal femur BMD, using a long term quantification of daily activity based on the
113 vertical component of the acceleration (Jämsä et al., 2006). It appears that strength
114 and overall fitness can be improved at any age through a carefully planned exercise
115 program. Unless the ability of the underlying physiologic systems essential for load116
bearing activity are restored, it may be difficult for many older women to maintain a
117 level of activity essential for protecting the skeleton from further bone loss (ACSM,
118 1995).
119 Sports Biomechanics includes the study of recreational physical activity, none
120 as Exercise Biomechanics. Two areas of research are of major interest: 1) the
121 quantification or estimation of mechanical load acting on the biological structures;
12
122 and 2) the study of biological effects of locally acting forces on living tissue; effects
123 such as growth and development or overload and injuries (Brüggemann, 2005).
124 The major biological effects of forces include changes in the development of
125 biological tissue and transportation of nutrients through the human body (Nigg,
126 2000). The effects of biomechanical loading applied on the Musculoskeletal System
127 can be either biopositives or bionegatives. Load repetition generally does not
128 result in injury during normal activity, although it has been suggested that repeated
129 impacts such as the collision of the foot with the ground during locomotion can result
130 in microtrauma (Hamill & Caldwell, 2001). Also, the magnitude of GRF has been
131 associated, although never verified, with the high incidence of lower extremities
132 injuries in fitness instructors (Rousanoglou & Boudolos, 2005).
133 Understanding the magnitude of loading is important for exercise prescription
134 and to design rehabilitation programs. The vertical peak-GRF allows to characterize
135 movement in terms of biomechanical loading. It has been suggested that there is an
136 optimal amount of loading that healthy individuals should maintain and that loading
137 above a certain limit might be related to the risk of injury (Shaw et al., 2001). High
138 skeletal loading intensity has been defined as peak-GRF of greater than 4 times
139 body-weight (BW), moderate intensity as 2-4 BW, and low intensity as GRF less than
140 2-BW, and a minimum osteogenic effect was related to 1-2 BW (Witzke & Snow,
141 2000; Shaw et al., 2001; Turner & Robling, 2003).
142 The human body has a number of mechanisms by which load is attenuated.
143 On one hand, the body has structures such as fat pads on the plantar surface of the
144 foot, cartilage in the joints and bone, and soft tissues surrounding the bone. On the
145 other hand, there are also particular motions of the segments that attenuate shock. In
13
146 the lower extremity, these include knee flexion, subtalar pronation, and ankle
147 dorsiflexion (Hamill & Caldwell, 2001).
148 Step-Exercise was described in a previous study (Santos-Rocha et al., 2006).
149 Most participants are female. Besides its cardiovascular benefits (Stanforth et al.,
150 1993; Scharff-Olson et al., 1996; Kraemer et al., 2001; Kin Ilser et al., 2001) the
151 structure of exercise sessions, concerning rate and magnitude of skeletal loading,
152 may improve the osteogenic potential of physical activity (Cullen et al., 2001; Turner
153 & Robling, 2003) because this activity involves a large number of loading cycles
154 during each session (Santos-Rocha et al., 2006). When Step-ReebokTM program was
155 presented its proponents claimed that ground reaction forces (GRF) were similar to
156 those of walking (Reebok University Press, 1994). Two forms of controlling the
157 intensity of the workout are by adjusting stepping-rate (125-150 beats-per-minute –
158 bpm); and by selecting the types of movements included in choreography (e.g.
159 propulsive movements). The characterization of Step Exercise has shown that
160 classes are performed with a mean (±sd) stepping rate of 135±5 bpm and the mean
161 (±sd) number of loading cycles performed was 4194.1±1055.2, ranging from 1874 to
162 7250, which might help to meet the recommendation of 10,000 steps a day (Wilde et
163 al., 2001).
164 A major concern is how to control the intensity of the workout, maintaining safe
165 and effective levels of mechanical load. The GRF of a Step session depend on the
166 type and number of movements performed (Santos-Rocha et al., 2006). Regular
167 exposure to moderately high magnitudes of force is desirable within certain levels,
168 because mechanical stress will induce adaptation on biological structures, however
169 the same forces might produce undesirable effects such as discomfort, pain and
170 injury, especially when forces are too repetitive in a period of time (Miller, 1990; Nigg
14
171 et al., 1995). Several authors referred that Step-Exercise seems to induce greater
172 loading than walking, and at increased stepping-rates its impact loading could be
173 compared to those obtained during comfortable running and high impact aerobics,
174 but with lower risk of injury (Farrington & Dyson, 1995; Bezner et al., 1996; Hecko &
175 Finch, 1996; Maybury & Waterfield, 1997; Williford et al., 1998; Santos-Rocha et al.,
176 2002).
177 Most studies with Step-Exercise, reported the effects of vertical peak-GRF
178 during the descending-phase of basic-step (Dyson & Farrington, 1995; Farrington &
179 Dyson, 1995; Bezner et al., 1996; Hecko & Finch, 1996; Tagen & Zebas, 1996;
180 Maybury & Waterfield, 1997; Scharff-Olson et al., 1997; Wieczorek et al., 1997;
181 Machado & Abrantes, 1998; Santos-Rocha et al., 2002; Santos-Rocha & Veloso,
182 2007). Few references reported the internal loading during Step-Exercise (Bezner et
183 al., 1996; Santos-Rocha & Veloso, 2004).
184 Also, one may be interested in the magnitude or in how fast the force is
185 increasing or decreasing. The loading-rate describes this behavior. The quantification
186 of the initial part of the vertical GRF curve may be effectively characterized by the
187 loading-rate, due to the absence of an impact peak in certain cases. It is often
188 assumed that the loading-rate is associated with the development of movement189
related injuries (Nigg, 2000).
190 We hypothesized that Step-Exercise is a low to moderate activity, and the
191 step-patterns with propulsion should present higher load than non-propulsive
192 movements, and loading increases with faster stepping-rate. Our purposes were to
193 investigate the differences that exist between four stepping-rate conditions
194 (125/130/135/140-bpm) and ascending and descending-phases of four step-patterns
15
195 (basic-step/knee-lift/run-step/knee-hop) in the vertical-1st-peak (FZ) and in the
196 vertical-1st-peak loading-rate (LR-FZ), during Step-Exercise.
197
198 METHODS
199 Eighteen Step-experienced females (mean±sd age 29.1±6.8 years; body mass
200 58.9±6.4kg; height 1.66±0.06m; Caucasian) with no history of lower limb trauma or
201 disease, volunteered to participate in the study. These women were experienced
202 fitness instructors who were certified and/or graduate in sport sciences and
203 possessed at least 3 years of teaching experience. They were led through a
204 sequence of 8 stepping tasks: right-basic-step, right-knee-lift, left-basic-step, left205
knee-lift, right-run-step, right-knee-hop, left-run-step, left-knee-hop. This procedure
206 was adopted in order to ensure mechanical balance between both lower limbs. No
207 arm movements were added. Verbal instruction was provided during the tests.
208 Fitness music was used to maintain cadence. All experimental trials were conducted
209 in a “crescent cadence” order. These procedures were adopted so the result would
210 reflect typical class conditions. Body-weight was measured using the Kistler force211
platform. The study was approved by the review committee of the Faculty. The
212 subjects were allowed to familiarize to each speed before data collection, and was
213 given approximately 60-90s of rest between trials so as to reduce the potential
214 effects of fatigue. In order to reduce error participants wore similar shoes, because
215 the type of footwear influence braking and propulsive forces, and alter foot
216 mechanics (Hennig & Milani, 1995; Mitchell et al., 1996).
217 Our previous study showed that metal force-platforms surfaces are suitable to
218 assess mechanical load of stepping, with experienced subjects (Santos-Rocha &
219 Veloso, 2007). The movements were performed on the AMTI (Advanced Mechanical
16
220 Technology, Inc, Watertown, MA) force-platform (17cm height) for stepping-up
221 (substituting the step-bench) and on the KISTLER (Kistler AG, Winterthur,
222 Switzerland) force-platform on ground level for stepping-down. Acqknowledge-3.7.3.
223 (BIOPAC Systems, Inc., Goleta, CA) was used to collect GRF at 1000-Hz and
224 process data. Data were smoothed with a Hamming low pass digital filter of 8-Hz.
225 Peak values were collected and normalized to BW in Excel (Microsoft Corporation,
226 USA). Loading-rate (N/s) was calculated (loading-rate=peak-force-N/time-to-peak-s)
227 and normalized to BW/s. Figure 1 represents the identification of the movements
228 studied, and shows the phases of reception during which the peak values were
229 collected.
230 Using SPSS (Statistical Package for the Social Sciences, Chicago, IL) the
231 vertical-1st peak (FZ) in BW and the vertical-1st peak loading-rate (LR-FZ) in BW/s
232 were analyzed statistically. Descriptive statistics are reported and a one-way ANOVA
233 for repeated measures (RM) was used to determine whether there where significant
234 differences between the conditions of stepping-rate and step-patterns, resulting in
235 two within-subjects factors. Prior to perform RM, Kolmogorov-Smirnov normality test
236 and Mauchly’s test of sphericity were conducted. In the cases sphericity was not
237 assumed the Huynh-Feldt correction was used. The pairwise comparisons with the
238 Bonferroni confidence interval adjustments were used to identify where differences
239 could be found. The level of statistical significance was set at p≤0.050 (Vincent,
240 2005).
241
242 RESULTS
243 The results showed that during stepping at different cadences the vertical GRF
244 curves were very regular and repetitive among subjects, despite different interval
17
245 time among conditions. We observed the absence of impact peaks in the movements
246 analyzed. Table 1 shows the descriptive statistics of FZ and LR-FZ. Table 2 shows
247 the results of ANOVA-RM and Bonferroni pairwise comparisons of the parameters
248 analyzed, as well as the summary of the confirmation of the hypothesis. The test of
249 within-subjects effects has shown no interaction between step-pattern and stepping250
rate in LR-FZ (descending-phase). There was interaction between conditions in
251 relation to: FZ (ascending-phase, p=0.001; descending-phase, p=0.011) and LR-FZ
252 (ascending-phase, p=0.002).
253
254 DISCUSSION
255 The GRF may provide a surrogate measure for the strain experienced by bone on a
256 variety of loading activities such as Step movements. The analysis of GRF has
257 shown that higher loads occur during the reception on the step-bench (in propulsion
258 movements: run-step and knee-hop) and during the reception on the ground (in non259
propulsion movements: basic-step and knee-lift). The results of FZ in basic-step
260 (descending-phase) were greater than those reported by other authors that used
261 slower cadences (120-bpm) (Farrington & Dyson, 1995; Bezner et al., 1996; Maybury
262 & Waterfield, 1997) but are in line with those obtained by Teriet and Finch (1997) and
263 with those obtained in our previous studies (Santos-Rocha et al., 2002). In knee-lift
264 (descending-phase) the results were greater than those reported by Farrington and
265 Dyson (1995) that used slower cadences (120-bpm). The results in both phases are
266 in line with those obtained by Panda (2003). In run-step the mean FZ was 2.3-BW
267 (ascending-phase) and 1.8-BW (descending-phase). Tagen and Zebas (1996)
268 reported 2.5-BW during ascending-phase of run (126-bpm). The results of FZ in
269 knee-hop (ascending-phase) are in line with those reported by Machado and
18
270 Abrantes (1998) that also used slower cadences (120-bpm). The results for both
271 phases of all movements performed at 130 and 140-bpm were around 0.1-0.2
272 smaller than those obtained in our previous studies using pressure insoles (Santos273 Rocha & Veloso, 2007). In walking FZ had a maximum value of 1-1.2 BW, and in
274 running, can achieve 3-5 BW (Miller, 1990). Therefore, Step-Exercise seems to
275 produce greater loading than walking and at increased stepping-rates its loading
276 could be compared to those obtained during comfortable running.
277 The results obtained for vertical peak-forces suggest that Step-Exercise is a
278 low to moderate activity, depending on the inclusion of non-propulsion or propulsion,
279 and stepping-rate (with experienced participants). Our results support the conclusion
280 of Scharff-Olson et al. (1997) that experience with Step-Exercise may afford an ability
281 to make uniform and force-absorbing adjustments in FZ at increased speeds. Teriet
282 and Finch (1997) suggested that the faster loading and unloading-rates of the
283 musculature due to the faster stepping-rates (122 to 130-bpm) caused less control of
284 the movement, resulting in a 4% increase in the FZ and therefore, the use of faster
285 tempos in a beginning level class could be a source of elevated risk for potential
286 injury.
287 The time of peak FZ, ranged 0.20-0.28s (ascending-phase) and 0.21-0.22s
288 (descending-phase). The interval time decreased with stepping-rate, meaning that
289 the same movement has to be performed in the same form but with less time. This is
290 reflected by the increase in loading-rate. Loading-rate was associated to 77 BW/s in
291 running speed at 3m/s (Miller, 1990). In the present study, the mean LR-FZ
292 increased with stepping-rate, and the greatest value was found in ascending-phase
293 of run-step. In descending-phase it increased significantly with stepping-rate. The
19
294 larger peaks and loading-rates indicate a loss of shock absorbing capacity. This
295 might increase their susceptibility to lower extremity overuse injuries.
296 The results indicate that lower extremity external loading can be effectively
297 controlled by varying stepping-rate during Step classes, and by choosing movements
298 mechanically similar to those analyzed in the present study. As an example, the run299
step clearly induced greater forces and loading-rate, which might be more related to
300 injury.
301 These findings indicate the relative contributions of stepping-rate and different
302 choreographic movements to the external forces experienced during Step-Exercise.
303 Further research is needed focusing other step-patterns in order to select those that
304 are more appropriate to be included in Exercise and Rehabilitation programs. The
305 present investigation provides biomechanical data that may be used as a basis of
306 comparison with patients, elderly people and beginners that participate in Step
307 programs. However, the present results are based on a sample of 18 experienced
308 and physically active instructors, thus, both kinematics and force characteristics of
309 the tasks may be different if participants with less experience in Step are used, and
310 establishing norms for other populations requires understanding other factors that
311 affect GRF. Also, these results are related to the mechanical characteristics of this
312 physical activity and might be analyzed under the ergonomic perspective, since the
313 group of subjects was constituted by experienced Step instructors. The results
314 suggest that experienced steppers are capable of stepping at different cadences,
315 with generally similar patterns of kinematics and kinetics.
316 Our results showed that increasing step frequency leads to an increase in the
317 mechanical load, which appears to be supported by adaptations of the movement
318 technique which might be related with the increasing GRF. However, if technique
20
319 adaptations occur, especially in the knee joint, together with greater GRF and
320 moments of force and decreased time for contact and force transfer, the stepping321
rate, being one of the most important determinants of exercise intensity, particularly
322 above 135-bpm, should be chosen carefully in classes, having always in
323 consideration the participants’ experience in this activity.
324 The results contribute to understand how skilled participants deal with the
325 increase of the external load during Step-Exercise. Skilled participants appear to
326 control the increase of stepping-rate by means of knee and ankle adaptations. These
327 joints might be in greater risk of injury in the case of overuse, especially the knee
328 joint. In order to prevent injury, proper instruction should be provided in relation to
329 foot placement on the step-bench and on the ground, as well as information
330 concerning knee flexion. Our results indicate that lower extremity external loading
331 can be effectively controlled by varying stepping-rate during Step classes and
332 selecting step-patterns. The results are also relevant to determine which movements
333 and cadences can be recommended to be included in rehabilitation programs where
334 walking and running are prescribed. Assuming that walking or running are “safe”
335 activities to be included in Exercise and rehabilitation programs, oriented stepping
336 exercise appear relatively safe with respect to the magnitude of loading.
337 In conclusion, Step-Exercise is performed using music that sets movement
338 cadence which involves the repetition of exercises that induce peak-GRF of low
339 magnitude moderate activity (1-2.5 BW), depending on step-patterns included, but of
340 high frequency (3750-4050 loading cycles during a 30-min session, depending on the
341 stepping-rate, using music speed at 125/135-bpm) (Santos-Rocha et al., 2006). We
342 suggest that this recreational activity may be included in bone health promotion
343 programs.
21
344
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489
27
490
.00000 3.33525 6.67050 10.00575
seconds
0.00
144.97
289.94
434.91
N
AMTI_Fx
0.00
436.00
872.01
1308.01
N
AMTI_Fz
0.00
495.81
991.61
1487.42
N
FZ
-315.19
-157.59
0.00
157.59
N
FX
Right
Basic
Step
Right
Run
Step
Left
Basic
Step
Left
Run
Step
Right
Knee
Lift
Left
Knee
Lift
Right
Knee
Hop
Left
Knee
Hop
GRF
491
492 Figure 1. Anterior-posterior (AMTI_Fx and FX) and vertical (AMTI_Fz and FZ)
493 components of the ground reaction force of one representative subject at 140 beats
494 per minute. The arrows identify the phases during which the peak values were
495 collected within the sequence of the 8 Step movements using the vertical component
496 of the ground reaction force, during the ascending (AMTI Fz) and descending (FZ)
497 phases of the movements: black arrows show basic-step; grey arrows show knee-lift;
498 black dashed arrows show run-step; and grey dashed arrows show knee-hop.
28
499 Table 1. Descriptive statistics of the peak vertical ground reaction force (FZ)
500 normalized to body weight (BW) and of the loading rate of the peak vertical ground
501 reaction force normalized to body weight per second (BW/s), during ascending phase
502 and descending phase of four Step-patterns (basic-step, knee-lift, run-step and knee503
hop) performed at four stepping-rates (125, 130, 135 and 140 bpm).
BASIC-STEP KNEE-LIFT RUN-STEP KNEE-HOP
BPM 125 130 135 140 125 130 135 140 125 130 135 140 125 130 135 140
ASCENDING PHASE – PEAK FZ GRF (BW)
Mean 1.2 1.2 1.2 1.2 1.3 1.2 1.3 1.3 2.1 2.2 2.2 2.3 1.8 1.8 1.8 1.8
sd 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.3 0.3 0.2 0.2 0.2 0.2 0.2
Min 1.0 1.0 1.0 1.0 1.0 1.1 1.1 1.0 1.7 1.5 1.6 1.9 1.5 1.5 1.5 1.5
Max 1.4 1.4 1.5 1.5 1.6 1.5 1.5 1.6 2.6 3.0 3.1 2.7 2.1 2.2 2.2 2.2
Range 0.4 0.5 0.4 0.5 0.6 0.5 0.4 0.6 0.9 1.5 1.5 0.9 0.6 0.8 0.7 0.7
DESCENDING PHASE – PEAK FZ GRF (BW)
Mean 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.8 1.7 1.7 1.8 1.8 1.6 1.6 1.6 1.6
sd 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.2 0.2 0.3 0.2 0.2 0.2 0.3 0.3
Min 1.3 1.3 1.3 1.2 1.2 1.3 1.3 1.3 1.4 1.3 1.4 1.4 1.2 1.2 1.1 1.1
Max 2.1 2.1 2.1 2.2 2.0 2.3 2.1 2.3 2.2 2.4 2.3 2.3 2.0 2.2 2.0 2.1
Range 0.7 0.8 0.8 1.0 0.8 1.0 0.8 1.0 0.8 1.1 0.9 1.0 0.8 1.0 1.0 1.0
ASCENDING PHASE – LOADING RATE PEAK FZ (BW/s)
Mean 5.8 5.9 6.0 6.3 4.9 5.1 5.1 5.5 8.7 9.0 9.2 10.2 6.5 6.8 6.6 7.2
sd 0.9 1.0 1.2 1.3 0.8 0.7 0.6 0.6 2.1 2.0 1.8 1.5 1.0 1.3 1.1 1.0
Min 4.0 3.9 4.1 4.1 3.5 3.9 4.1 4.4 5.4 4.8 5.7 6.8 4.5 4.8 4.9 5.3
Max 7.3 8.2 8.9 9.3 6.4 7.2 7.4 6.9 14.1 13.5 13.1 13.1 8.4 10.4 9.7 9.1
Range 3.3 4.3 4.7 5.2 3.0 3.3 3.4 2.5 8.7 8.7 7.4 6.3 3.8 5.6 4.8 3.8
DESCENDING PHASE – LOADING RATE PEAK FZ (BW/s)
Mean 8.1 8.2 8.5 8.5 7.4 7.9 8.3 8.5 7.8 8.3 8.5 8.5 7.4 7.5 7.8 7.7
sd 1.4 1.3 1.8 1.6 1.1 1.6 1.7 1.7 1.3 1.7 1.6 1.3 1.2 1.8 1.7 1.5
Min 4.9 5.9 6.3 5.8 4.7 4.5 5.8 5.1 4.7 6.2 5.2 6.3 4.4 4.8 4.8 5.4
Max 10.9 11.1 12.8 12.5 9.4 13.5 15.6 13.1 10.4 12.8 12.1 11.9 10.7 13.2 12.3 11.0
Range 6.0 5.2 6.5 6.7 4.8 9.0 9.7 8.0 5.6 6.7 6.9 5.6 6.3 8.4 7.5 5.6
504
505
29
506 Table 2. Summary of the results of the statistical analysis (ANOVA repeated
507 measures) performed with vertical peak ground reaction forces (FZ) parameters.
508 Significantly statistical differences (p≤0.050) were found among the following
509 conditions of stepping-rate and step-pattern:
STEPPING-RATE STEP-PATTERN
Peak FZ
ascending
phase
ANOVA-RM F(3,105)=12.652 (p=0.000)
All (p≤0.013); except 125-130 bpm;
except 135-140 bpm
Increases as stepping-rate increases
Hypothesis confirmed
F(2.086,73.005)=441.251 (p=0.000)
All (p=0.000)
Greater values in run-step
Hypothesis confirmed
Peak FZ
descending
phase
F(3,105)=5.901 (p=0.001)
125-135 bpm (p=0.001); 125-140 bpm
(p=0.015)
Increases as stepping-rate increases
Hypothesis confirmed
F(2.200,77.000)=14.301 (p=0.000)
basic-hop (p=0.000); knee lift-hop (p=0.003);
run-hop (p=0.000)
Hypothesis not confirmed
Loading rate FZ
ascending
phase
F(3,105)=17.838 (p=0.000)
125-140 bpm (p=0.000); 130-140 bpm
(p=0.000);
135-140 bpm (p=0.000)
Increases as stepping-rate increases
Hypothesis confirmed
F(2.398,83.925)=147.162 (p=0.000)
All (p=0.000)
Greater values in run-step
Hypothesis confirmed
Loading rate FZ
descending
phase
F(2.715,95.041)=8.432 (p=0.000)
125-135 bpm (p=0.000); 125-140 bpm
(p=0.000)
Increases as stepping-rate increases
Hypothesis confirmed
F(3,105)=8.770 (p=0.000)
basic-hop (p=0.000); run-hop (p=0.003)
Hypothesis not confirmed
510
511 Acknowledgements: POCI 2110 - POCI/DES/61761/2004
512 The authors wish to thank to all participants of this study; to Helô Isa André, MSc and
513 Maria João Valamatos, MSc (Faculty of Human Kinetics) and to Maria Fátima
514 Ramalho, MSc (Sport Sciences School of Rio Maior) for their help in data collection;
515 to Pedro Aguiar, MSc (National School of Public Health) and to Isabel Carita, PhD
516 (Faculty of Human Kinetics) for their advice in statistical procedures.
517
518 There are no competing interests.
WOMEN in SPORT and PHYSICAL ACTIVITY JOURNAL
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31 October 2008
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