Electromyographic Effect of Mat Pilates Exercise on the

ELECTROMYOGRAPHIC EFFECT OF MAT PILATES EXERCISE ON
THE BACK MUSCLE ACTIVITY OF HEALTHY ADULT FEMALES
Maryela O. Menacho, MSc, a Karen Obara, PT,b Josilene S. Conceição, PT,c Matheus L. Chitolina, PT,c
Daniel R. Krantz, PT,d Rubens A. da Silva, PhD, e and Jefferson R. Cardoso, PhD a
ABSTRACT
Objective: The purpose of this study was to examine back muscle activity during 3 traditional mat Pilates exercises.
Methods: Eleven healthy female volunteers, aged between 18 and 30 years, participated in this cross-sectional study.
Surface electromyography (sEMG) of lumbar extensor muscles was recorded simultaneously with kinematics data
to identify the phases of movement. Three mat Pilates back exercises were compared: (1) swimming, (2) single leg
kick with static prone back extension, and (3) double leg kick. Root mean square values of each muscle were
recorded with 2 pairs of surface electrodes placed bilaterally on one lumbar extensor muscle (at L5). During phases
of each exercise, sEMG signals were identified by video analysis. Electrical muscle activation was normalized by
the maximal voluntary isometric contraction and used to compare back muscle activity among exercises. A 2-way
repeated measures analysis of variance was performed to assess the differences in activation level during the exercises.
Results: The value of electrical muscle activity in the lumbar extensors ranged between 15% and 61% of MIVC for
the 3 types of Pilates mat work exercise. The swimming exercise increased lumbar extensor activity (29% on
average) in comparison to the other 2 Pilates conditions. Interestingly, the double leg kick exercise generated
significantly more lumbar extensor activity (26% on average) than the single leg kick.
Conclusions: For this group of participants, the swimming exercise increased muscle activation relative to the other 2
exercise modes. (J Manipulative Physiol Ther 2010;33:672-678)
Key Indexing Terms: Back Muscles; Electromyography; Rehabilitation; Exercise Therapy
xcessive fatigability of lumbar paraspinal muscles is
often associated with chronic low back pain (LBP).1
Poor back extensor muscle endurance is, furthermore, a predictor of first-time occurrence of LBP and of
E
a
Physical Therapist, Physical Therapy Department, Kinesiologic Electromyography and Kinematic Laboratory, Universidade
Estadual de Londrina, Londrina, PR, Brazil.
b
Student, Physical Therapy Department, Kinesiologic Electromyography and Kinematic Laboratory, Universidade Estadual de
Londrina, Londrina, PR, Brazil.
c
Physical Therapist, Private Practice in Maravilha, SC, Brazil.
d
Physical Therapist, Private Practice in Iraceminha, SC, Brazil.
e
Physical Therapist and Professor in the Master of Science in
Rehabilitation Program at UEL/UNOPAR, Centre for Research in
Health Sciences, Universidade Norte do Parana (UNOPAR),
Londrina, PR, Brazil.
Submit requests for reprints to: Prof. Jefferson R. Cardoso,
PhD, Physical Therapy Department, Kinesiologic Electromyography and Kinematic Laboratory, Universidade Estadual de
Londrina, Av Robert Rock, 60. CEP 86038-440, Londrina-PR,
Brazil (e-mail: [email protected]).
Paper submitted February 15, 2010; in revised form May 19,
2010; accepted June 8, 2010.
0161-4754/$36.00
Copyright © 2010 by National University of Health Sciences.
doi:10.1016/j.jmpt.2010.08.012
672
long-term back-related disability when assessed 4 weeks
postinjury.2,3 As concluded in a recent review, progressive
resistance exercises for back muscles have been successful
in increasing strength and/or endurance as well as
decreasing pain and/or disability among patients with LBP.4
There are several modes of exercise for improving the
muscular function of the back. In the area of spine
stabilization exercises, such as those that use floor mats or
balls, the Pilates method has been gaining recognition
recently as an optimal choice for improving spinal
stability as well as the strength and/or endurance of
trunk muscles (abdominal and lumbar).5 The weakness or
fatigue of trunk muscles can increase the risk of
neuromuscular deficits, which, according to Panjabi's
theory of the spinal stabilizing system, causes brief
uncontrolled intervertebral movements.6,7 An unstable
lumbar spine could contribute to tissue strain injury and
subsequently to chronic back pain.8
Pilates exercises, through the use of various approaches,
emphasize the strengthening of both abdominal and lumbar
muscles while promoting good posture and body
alignment.9 The Pilates method integrates movement of
the extremities in multiplane functional positions and
correct spinal alignment with breathing and core centering
Journal of Manipulative and Physiological Therapeutics
Volume 33, Number 9
using a simple mat (traditional approach) or equipment
(Reformer, for instance).10,11 Robinson et al9 further
suggest that Pilates exercise can be advocated as a
secondary maintenance stage of spinal stabilization rehabilitation treatment for recurrence prevention in patients
with LBP.
Few studies have investigated the electromyographic
(EMG) activity of back muscles during Pilates exercise.11
Some studies, however, have observed the EMG activity of
selected trunk muscles during specific spinal stabilization
exercises.12-14 Arokoski et al12 reported that some traditional lumbar stabilization exercise types such as quadruped, prone, and standing are effective for lumbar muscle
activation. Souza et al14 also observed significant back
muscle activity (20%-30% of maximal activity) in different
levels of quadruped exercise with ipsilateral leg raising.
However, to the authors' knowledge, no study has
investigated the activity of lumbar muscles during the
traditional Pilates mat exercises in the following: (1)
swimming (SW), (2) single leg kick (SLK) in the prone
position with static back extension, and (3) double leg kick
(DLK). The purpose of this study was to examine the effect
of 3 mat Pilates exercises (SW, SLK, and DLK) on the
EMG activity of back muscles.
METHODS
Subjects
Eleven healthy females, aged between 18 and 30 years,
were recruited on a voluntary basis (university students
and employees). The mean (standard deviation) characteristics of subjects were age = 22 (5) (year), height = 1.65
(0.6) (m), mass = 57.7 (8) (kg), and body mass index = 21
(1) (kg/m2). The exclusion criteria were as follows: back
pain in the previous year, surgery on the musculoskeletal
system of the trunk and legs, known congenital malformation of the spine or scoliosis, neurologic disease, current
pregnancy, abnormal blood pressure, the use of medication
to control cholesterol or triglyceride, or involvement in a
new physical training program. All subjects had a good
general physical aptitude and reported that they had never
before performed Pilates exercises. The subjects were
informed about the experimental protocol and the potential
risks of the study and gave written consent before their
participation. This study was previously approved by the
Ethics Committee of the Universidade Estadual de
Londrina, Londrina, Brazil (266/07).
Procedures
One session of approximately 2 hours was required for
the experiment. The same investigator performed the all
procedures and tasks with each subject to ensure
uniformity. All exercises were demonstrated by a physical
therapist trained in the Pilates method with experience as a
Menacho et al
Back Muscles Activity During Pilates
Pilates instructor. The first step in the evaluation was to
collect basic anthropometric measurements and to familiarize the subject with the equipment and the tasks. The
second step was to assess back muscle activation during 3
traditional Pilates exercises (details below). The 3 sets of
exercises were separated by 30 minutes of rest to minimize
the effects of fatigue and were carried out randomly to
control for possible confounding carryover effects.
Maximal Voluntary Isometric Contraction
For purposes of normalization, maximal voluntary
isometric contraction (MVIC) was performed for back
muscles to determine their maximal EMG activation. This
choice was based on MVIC due to characteristics of the
Pilates method, in which exercises are performed during
expiration at a self-controlled velocity. Moreover, seeing
that the range of motion in the spine is small during the
exercises used in this study, it was reasonable to assume
that there would be no significant change in muscle length
and thus no significant effect in the EMG/force relationship.
The subjects performed the MVIC while lying prone on a
bench and positioned so that their anterior-superior iliac
spines were aligned with the edge of the bench. The upper
body was suspended horizontally and unsupported off the
end of the bench, whereas the lower limbs (ie, thighs to feet)
were restrained with tight-fitting self-stick straps; the arms
were folded with hands crossed over opposite shoulders.
The subjects started MVIC with the trunk slightly flexed in
relation to horizontal and generated progressive back
extension efforts against resistance on the upper back
provided by an experienced physical therapist.15 Three
MVICs, lasting 5 seconds each, were performed with verbal
encouragement, allowing 5 minutes of rest between each.
The largest value of the maximal EMG activation (details in
processing signal) was retained as the MVIC.
Pilates Exercises
Ten minutes after the MVIC measurement and before
executing the Pilates exercises, the subjects performed
submaximal contractions to warm up, with stretching and
mobilization of the spine, including spine stretch forward
(stretching of the spine from the anterior trunk flexion in
sitting position) and saw (stretching of the spine and
combination of trunk forward flexion and rotation of the
spine in sitting position). The subjects then performed one
set of 8 repetitions lasting approximately 30 seconds for
each of the following Mat Pilates exercise types (Fig 1):
SW, SLK, and DLK. For SW, the subjects assumed a prone
position, with arms extended overhead and lifted the trunk
and legs during the execution of exercise (Fig 1A). For the
duration of each exercise, the subjects maintained the neck
in alignment with the spinal column (a principle of Pilates).
The SLK exercise started with lumbar static hyperextension
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November/December 2010
Fig 1. Phases of exercise movement during 3 traditional Pilates conditions on a mat: (A) SW; (B) SLK, with prone static back extension;
and (C) DLK.
(eg, maintenance of a static lordotic lumbar posture during
the entire exercise) with hands placed on the mat (Fig 1B).
The subjects alternated flexion and extension of the legs,
such as kicking the heel toward the buttock for 2 pulses and
then switching legs. Double leg kick (Fig 1C) was similar to
SLK, except that subjects executed dynamic movements
including simultaneous lifting of the legs and arms with
concentric back extension (eg, extending the spine). The
Pilates principles of body alignment, breathing control, and
abdominal muscle control were emphasized throughout the
exercise session. The EMG signals and video data were
recorded simultaneously during the 3 sets.
Electromyography
An 8-channel electromyography system (MP150; BIOPAC Systems Inc, Aero Camino Goleta, CA), consisting of
a signal conditioner with a band-pass filter with cutoff
frequencies at 20 to 450 Hz, an amplifier gain of 2000 and a
common mode rejection ratio of more than 120 dB was used
to obtain the biological signals. All data were collected using
specific software for acquisition and analysis (Acqknowledge 3.9.1; BIOPAC Systems Inc). Analog-to-digital
conversion (16 bits) was set up with an antialiasing filter
and a sampling frequency of 2000 Hz for each channel and
an input range of 10 mV. Active bipolar electrodes were
connected to a high impedance preamplifier (1.0 × 1012 Ω).
After the skin at the electrode sites was shaved and
abraded with 70% alcohol, the electrodes were positioned
bilaterally over the multifidus (MU) at the L5 level (see
Fig 2; MU-L5-Right [R] and MU-L5-Left [L]), following
the recommendations of the Surface-EMG for the Non
Invasive Assessment of Muscle, 3 cm from the midline of
L5 spinous process. The interelectrode (center-to-center)
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Menacho et al
Back Muscles Activity During Pilates
alternate movements of leg flexion with static back
hypertension. For DLK, the RMSEXE(r) was also computed
for each repetition of the simultaneous lifting of the legs
and arms with concentric back extension movement. In
both exercises (SLK and DLK), the RMSEXE(r) values were
then averaged over 5 repetitions to give a single value
(RMSEXE(mean of r)). Finally, the activation level (%) was
computed for each muscle and Pilates exercise using the
following equation:
SW:
Activation level ðkÞ = ½ðRMSEXE =RMSMAX × 100kÞ
SLK and DLK:
:
Acivation level ðkÞ = RMSEXEðmean of rÞ =RMSMAX × 100k
Fig 2. Electrode position on lumbar extensor muscle at L5 site.
distance was 2 cm, taking muscle fiber direction into
account.16 The reference electrode was placed on the
nondominant wrist (in the styloid process of the ulna).
Processing EMG Signal
All EMG data processing was performed and analyzed
using Matlab subroutines (7.7.0; The MathWorks Inc,
Natick, MA). A notch filter was used for the EMG signals,
removing frequencies at 60 Hz. From the EMG signals
corresponding to the MVICs, a root mean square (RMS)
processing method was executed on successive 250millisecond (512 points) time windows (50% overlapped).
For each muscle, the peak RMS value across all MVIC
trials represented the maximal EMG activity (RMSMAX).
RMSMAX was used to compute the muscle activation level,
which is the percentage of EMG amplitude relative to the
maximal EMG obtained from largest interexercise MVIC.
The execution of each exercise lasted an average of
30 seconds. However, for EMG data analysis just the first
20 seconds of activity were considered. This was set to
minimize the confounding effect of muscle fatigue on EMG
activation analysis. A standard video camera 30 Hz (Sony)
linked to the computer was used to manually synchronize
the recording of both exercise performance and sEMG
data. Thus, one person was filming while another began
signal collection and then the subjects performed the
exercise. Subsequently, the video was used to identify the
signal corresponding to the phases of each movement. For
SW, RMS values (250 milliseconds, 50% overlapped)
were computed using EMG signals from the concentric
back extension phase while lifting the arms and legs. For
each muscle, the mean RMS value was then computed to
represent the mean RMS activity during the exercise
(RMSEXE, EXE = exercise). For SLK, the RMSEXE(r)
(r representing the number of repetitions) was computed
for each repetition (lasting 2 seconds on average) from
Statistical Analysis
All variables were normally distributed, as verified by
the Shapiro-Wilk test. A 2-way repeated measures analysis
of variance (2 muscles × 3 Pilates) on the Pilates factor
(SW, SLK, and DLK) was performed to assess the
differences in activation level during the exercises. Post
hoc analyses were performed, when necessary, using the
Tukey test. All statistical analyses were carried out with
SPSS statistical software (version 15; SPSS Inc, Chicago,
IL) with an α of .05 set as statistical significance.
RESULTS
The activation level of the lumbar extensor muscles
ranged between 15% and 61% of MVIC among the 3
Pilates exercises. No significant interaction (P ≥ .05) was
found between muscles and Pilates exercises for the
activation level variable (Table 1). In both muscles, SW
significantly increased muscle activation (29% on average)
compared to SLK and DLK (see Table 1). Also, DLK
generated significantly more activity in the 2 lumbar
extensor muscles than did SLK (Table 1). These results
are further illustrated in Figure 3 with muscle data pooled
because no significant differences between side muscles
were found during the 3 exercise types (P = .09).
DISCUSSION
The Pilates method has been considered an optimal
exercise modality for improving spinal stability as well as
the strength and/or endurance of lumbar muscles.5 Several
studies12,14,17,18 have investigated the activation of trunk
extensor muscles during different modalities of back
extension exercises to determine which would best improve
back strength and endurance.
However, regarding Pilates exercises, few studies10,11
have assessed the recruitment pattern of trunk muscles
during exercise. Endleman and Critchley10 evaluated trunk
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Table 1. Activation values (% MVIC) of the lumbar extensor muscles during mat Pilates exercises
Pilates exercises
Variable
Muscles
Activation (MVIC %)
MU-L5-R
MU-L5-L
SW
61 (21)
57 (14)
P Analysis of variance
SLK
DLK
Muscles
Pilates
Interaction
19 (11)
15 (10)
47 (21)
39 (17)
0.0091
b.001
Tukey test results
SW N SLK, DLK
DLK N SLK
0.655
Analysis of variance results: main effects on muscles in the Pilates exercises. Values are presented as mean (SD).
The significant differences were identified with bold characters. Muscles: MU-L5-R indicates multifidus at the L5 right side level; MU-L5-L, multifidus at
the L5 left side level; N, identifies more back activation between conditions from Tukey post hoc test. Pilates exercises: swimming (SW), single leg kick
(SLK) in the prone position with static back extension, and double leg kick (DLK).
Fig 3. Activation level values (error bars correspond to standard
deviations) pooled across muscles during the three Pilates
conditions: SW; SLK, with prone static back extension; and
DLK. For more details, see Table 1.
muscle activity (abdominal only) during traditional and
reformer Pilates approaches and only with the use of
ultrasound measurements of muscle thickness, which do not
correspond to the main outcome measure of the present
study. Although Petrofsky et al11 observed back extensor
muscle activity using EMG, they evaluated Pilates modalities (90° and 45° squat, right and left abduction and hip
extension) with respect to resistance devices and other
muscle groups, not necessarily targeting back muscles.
To the authors' knowledge, this is the first study
comparing the activity of lumbar muscles during traditional
mat Pilates exercises. Three different mat Pilates exercises
were assessed: SW, SLK, and DLK. The results of this
study demonstrated that a progression of Pilates exercises
can be assigned in order of back muscle activation load.
For example, back activity during SLK was low, on
average 17% of maximal EMG activity/MVIC (Fig 3), and
related to static lumbar hyperextension (ie, maintenance of a
static lordotic lumbar posture). In fact, this exercise
emphasizes only an alternating contraction during flexion
and extension of legs without overloading the back muscles.
Double leg kick activated the back muscles on average
42% of MVIC. This exercise involves intermittent concentric action of the trunk muscles with simultaneous back and
bilateral leg extension while prone with the hands placed
behind the back. A significant increase in back extensor
activity is observed during prone back extension exercises
when the relative trunk load is increased by modifying hand
and lower limb position.18,19 The effect could be related to
the relative weights of each segment (trunk + legs + arms) on
the rotation axis of the lumbar spine during this exercise.
Interestingly, the magnitude of this effect is comparable to
the 53% difference found in prone back extension exercises,
which require lifting the trunk and legs.18
The main results of this study were that SW led to more
lumbar extensor activity (29% on average) than the other
exercises (Fig 3). As stated above, this may be related to load
and moment arm length in this exercise. Generally, more
lumbar torque is exerted when a load is positioned further
from the axis of rotation along the moment arm. 20
Swimming is performed with dynamic movements, moving
the arms in the extended position and lifting the trunk and
legs during the execution of exercise. Therefore, placing
the hands and arms (part of the torso mass) further away
from the axis of rotation of the lumbar spine results in a
progressive increase in back muscle activity, as reported in
other studies.12,14,18,19 Plamondon et al18 found a peak level
of 61% of maximum lumbar muscle activity in an exercise
similar to SW that does not advocate Pilates principles,
which agrees with the results of the present study.
Moreover, Sekendiz et al21 showed that Pilates SW
exercise was efficient at increasing the strength and
endurance of trunk muscles in healthy adult females.
Based on our results, the 59% back activation achieved
during this exercise would be sufficient to elicit physiologic
changes and subsequently localize the effects of endurance
training on the back muscles.
Although several studies have investigated back muscle
activation during a range of back extension exercises such
as specific spinal stabilization exercises,13,14 prone back
extension, 18,22 roman chair, 17,23 and machine-based
exercises,24,25 none used Pilates principles (body alignment, breathing control, and abdominal control). The
Journal of Manipulative and Physiological Therapeutics
Volume 33, Number 9
results of this study will help in the design of an exercise
program specifically for back muscles using a Pilates
approach. As suggested in a recent review,4 specific back
exercises are more efficient for the treatment of LBP. Mat
Pilates work is simpler and more cost-efficient for
strengthening lumbar extensors than exercise using
machines or dynamometers. However, it is still unclear if
the Pilates' method provides similar overload stimulus
compared to machines for eliciting strength and endurance
gains in back muscles. Further studies are required to
compare the muscle activation in these exercises with
different populations and age groups, as well as with other
exercises types (eg, Pilates vs Roman chair and/or Pilates vs
machines). This measure could provide a better understanding of the effect of exercise on muscle and become a
prerequisite for the prescribing of spine stabilization,
endurance, or muscular strength training.
Limitations
This study has some limitations that need to be addressed.
These results only apply to traditional mat Pilates exercises.
They cannot automatically be generalized to patients with
LBP, who may have different back activation patterns,26,27
nor to male subjects, because some studies have found a sex
effect on back activation.12,28 The activation of abdominal
muscles and hip extensors was not assessed. Furthermore,
these results apply only to superficial lumbar muscles seeing
that no deep back muscles were investigated using
intramuscular EMG.
CONCLUSION
The electrical muscle activity of lumbar extensors
ranged from 15% to 61% during 3 mat Pilates exercises.
In both muscles, the SW exercise significantly increased
muscle activation (29% on average) relative to the other 2
exercise modes. This exercise may be a useful way to focus
the effects of endurance training on the back muscles.
Practical Applications
• The swimming exercise significantly increased
muscle activation compared to single leg kick
and double leg kick.
• The single leg kick is an exercise that emphasizes only an alternating contraction during
flexion and extension of legs without overloading the back muscles.
ACKNOWLEDGMENT
The authors wish to thank the Araucaria Research
Foundation for the fellowship awarded to Rubens A. da
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Back Muscles Activity During Pilates
Silva, a visiting Professor and researcher at the University
involved in this study and in the Master of Science in
Physical Education Program, and by the Basic and Applied
Research Program grant no. 14/08-10069 from the
Araucaria Research Foundation.
FUNDING SOURCES AND POTENTIAL CONFLICTS OF INTEREST
No funding sources or conflicts of interest were reported
for this study.
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