emg pilates

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, PhDa

a Physical Thegic ElectromyogEstadual de Lond

b Student, Phymyography and KLondrina, Londri

c Physical Thed Physical Thee Physical The

Rehabilitation PrHealth Sciences,Londrina, PR, Br

Submit requePhD, Physical Traphy and KineLondrina, Av RoBrazil (e-mail: je

Paper submitt2010; accepted J

0161-4754/$3Copyright ©doi:10.1016/j.

672

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 datato identify the phases of movement. Three mat Pilates back exercises were compared: (1) swimming, (2) single legkick with static prone back extension, and (3) double leg kick. Root mean square values of each muscle wererecorded with 2 pairs of surface electrodes placed bilaterally on one lumbar extensor muscle (at L5). During phasesof each exercise, sEMG signals were identified by video analysis. Electrical muscle activation was normalized bythe maximal voluntary isometric contraction and used to compare back muscle activity among exercises. A 2-wayrepeated 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 forthe 3 types of Pilates mat work exercise. The swimming exercise increased lumbar extensor activity (29% onaverage) in comparison to the other 2 Pilates conditions. Interestingly, the double leg kick exercise generatedsignificantly 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 2exercise modes. (J Manipulative Physiol Ther 2010;33:672-678)
Key Indexing Terms: Back Muscles; Electromyography; Rehabilitation; Exercise Therapy
Excessive fatigability of lumbar paraspinal muscles isoften associated with chronic low back pain (LBP).1

Poor back extensor muscle endurance is, further-more, a predictor of first-time occurrence of LBP and of

rapist, Physical Therapy Department, Kinesiolo-raphy and Kinematic Laboratory, Universidaderina, Londrina, PR, Brazil.sical Therapy Department, Kinesiologic Electro-inematic Laboratory, Universidade Estadual dena, PR, Brazil.rapist, Private Practice in Maravilha, SC, Brazilrapist, Private Practice in Iraceminha, SC, Brazilrapist and Professor in the Master of Science inogram at UEL/UNOPAR, Centre for Research inUniversidade Norte do Parana (UNOPAR)

azil.sts for reprints to: Prof. Jefferson R. Cardosoherapy Department, Kinesiologic Electromyog-matic Laboratory, Universidade Estadual debert Rock, 60. CEP 86038-440, [email protected]).ed February 15, 2010; in revised form May 19une 8, 2010.6.002010 by National University of Health Sciencesjmpt.2010.08.012

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long-term back-related disability when assessed 4 weekspostinjury.2,3 As concluded in a recent review, progressiveresistance exercises for back muscles have been successfulin increasing strength and/or endurance as well asdecreasing pain and/or disability among patients with LBP.4

There are several modes of exercise for improving themuscular function of the back. In the area of spinestabilization exercises, such as those that use floor mats orballs, the Pilates method has been gaining recognitionrecently as an optimal choice for improving spinalstability as well as the strength and/or endurance oftrunk muscles (abdominal and lumbar).5 The weakness orfatigue of trunk muscles can increase the risk ofneuromuscular deficits, which, according to Panjabi'stheory of the spinal stabilizing system, causes briefuncontrolled intervertebral movements.6,7 An unstablelumbar spine could contribute to tissue strain injury andsubsequently to chronic back pain.8

Pilates exercises, through the use of various approaches,emphasize the strengthening of both abdominal and lumbarmuscles while promoting good posture and bodyalignment.9 The Pilates method integrates movement ofthe extremities in multiplane functional positions andcorrect spinal alignment with breathing and core centering

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http://dx.doi.org/10.1016/j.jmpt.2010.08.012

673Menacho et alJournal of Manipulative and Physiological TherapeuticsBack Muscles Activity During PilatesVolume 33, Number 9

using a simple mat (traditional approach) or equipment(Reformer, for instance).10,11 Robinson et al9 furthersuggest that Pilates exercise can be advocated as asecondary maintenance stage of spinal stabilization reha-bilitation treatment for recurrence prevention in patientswith LBP.

Few studies have investigated the electromyographic(EMG) activity of back muscles during Pilates exercise.11

Some studies, however, have observed the EMG activity ofselected trunk muscles during specific spinal stabilizationexercises.12-14 Arokoski et al12 reported that some tradi-tional lumbar stabilization exercise types such as quadru-ped, prone, and standing are effective for lumbar muscleactivation. Souza et al14 also observed significant backmuscle activity (20%-30% of maximal activity) in differentlevels of quadruped exercise with ipsilateral leg raising.However, to the authors' knowledge, no study hasinvestigated the activity of lumbar muscles during thetraditional Pilates mat exercises in the following: (1)swimming (SW), (2) single leg kick (SLK) in the proneposition with static back extension, and (3) double leg kick(DLK). The purpose of this study was to examine the effectof 3 mat Pilates exercises (SW, SLK, and DLK) on theEMG activity of back muscles.

METHODS

SubjectsEleven healthy females, aged between 18 and 30 years,

were recruited on a voluntary basis (university studentsand employees). The mean (standard deviation) characte-ristics 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: backpain in the previous year, surgery on the musculoskeletalsystem of the trunk and legs, known congenital malfor-mation of the spine or scoliosis, neurologic disease, currentpregnancy, abnormal blood pressure, the use of medicationto control cholesterol or triglyceride, or involvement in anew physical training program. All subjects had a goodgeneral physical aptitude and reported that they had neverbefore performed Pilates exercises. The subjects wereinformed about the experimental protocol and the potentialrisks of the study and gave written consent before theirparticipation. This study was previously approved by theEthics Committee of the Universidade Estadual deLondrina, Londrina, Brazil (266/07).

ProceduresOne session of approximately 2 hours was required for

the experiment. The same investigator performed the allprocedures and tasks with each subject to ensureuniformity. All exercises were demonstrated by a physicaltherapist trained in the Pilates method with experience as a

Pilates instructor. The first step in the evaluation was tocollect basic anthropometric measurements and to famil-iarize the subject with the equipment and the tasks. Thesecond step was to assess back muscle activation during 3traditional Pilates exercises (details below). The 3 sets ofexercises were separated by 30 minutes of rest to minimizethe effects of fatigue and were carried out randomly tocontrol for possible confounding carryover effects.

Maximal Voluntary Isometric ContractionFor purposes of normalization, maximal voluntary

isometric contraction (MVIC) was performed for backmuscles to determine their maximal EMG activation. Thischoice was based on MVIC due to characteristics of thePilates method, in which exercises are performed duringexpiration at a self-controlled velocity. Moreover, seeingthat the range of motion in the spine is small during theexercises used in this study, it was reasonable to assumethat there would be no significant change in muscle lengthand thus no significant effect in the EMG/force relationship.The subjects performed the MVIC while lying prone on abench and positioned so that their anterior-superior iliacspines were aligned with the edge of the bench. The upperbody was suspended horizontally and unsupported off theend of the bench, whereas the lower limbs (ie, thighs to feet)were restrained with tight-fitting self-stick straps; the armswere folded with hands crossed over opposite shoulders.The subjects started MVIC with the trunk slightly flexed inrelation to horizontal and generated progressive backextension efforts against resistance on the upper backprovided by an experienced physical therapist.15 ThreeMVICs, lasting 5 seconds each, were performed with verbalencouragement, allowing 5 minutes of rest between each.The largest value of the maximal EMG activation (details inprocessing signal) was retained as the MVIC.

Pilates ExercisesTen minutes after the MVIC measurement and before

executing the Pilates exercises, the subjects performedsubmaximal contractions to warm up, with stretching andmobilization of the spine, including spine stretch forward(stretching of the spine from the anterior trunk flexion insitting position) and saw (stretching of the spine andcombination of trunk forward flexion and rotation of thespine in sitting position). The subjects then performed oneset of 8 repetitions lasting approximately 30 seconds foreach of the following Mat Pilates exercise types (Fig 1):SW, SLK, and DLK. For SW, the subjects assumed a proneposition, with arms extended overhead and lifted the trunkand legs during the execution of exercise (Fig 1A). For theduration of each exercise, the subjects maintained the neckin alignment with the spinal column (a principle of Pilates).The SLK exercise started with lumbar static hyperextension

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.

674 Journal of Manipulative and Physiological TherapeuticsMenacho et alNovember/December 2010Back Muscles Activity During Pilates

(eg, maintenance of a static lordotic lumbar posture duringthe 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 andthen switching legs. Double leg kick (Fig 1C) was similar toSLK, except that subjects executed dynamic movementsincluding simultaneous lifting of the legs and arms withconcentric back extension (eg, extending the spine). ThePilates principles of body alignment, breathing control, andabdominal muscle control were emphasized throughout theexercise session. The EMG signals and video data wererecorded simultaneously during the 3 sets.

ElectromyographyAn 8-channel electromyography system (MP150; BIO-

PAC Systems Inc, Aero Camino Goleta, CA), consisting of

a signal conditioner with a band-pass filter with cutofffrequencies at 20 to 450 Hz, an amplifier gain of 2000 and acommon mode rejection ratio of more than 120 dB was usedto obtain the biological signals. All data were collected usingspecific software for acquisition and analysis (Acqknow-ledge 3.9.1; BIOPAC Systems Inc). Analog-to-digitalconversion (16 bits) was set up with an antialiasing filterand a sampling frequency of 2000 Hz for each channel andan input range of 10 mV. Active bipolar electrodes wereconnected to a high impedance preamplifier (1.0 × 1012 Ω).

After the skin at the electrode sites was shaved andabraded with 70% alcohol, the electrodes were positionedbilaterally over the multifidus (MU) at the L5 level (seeFig 2; MU-L5-Right [R] and MU-L5-Left [L]), followingthe recommendations of the Surface-EMG for the NonInvasive Assessment of Muscle, 3 cm from the midline ofL5 spinous process. The interelectrode (center-to-center)

Fig 2. Electrode position on lumbar extensor muscle at L5 site.


distance was 2 cm, taking muscle fiber direction intoaccount.16 The reference electrode was placed on thenondominant wrist (in the styloid process of the ulna).

Processing EMG SignalAll 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 signalscorresponding to the MVICs, a root mean square (RMS)processing method was executed on successive 250-millisecond (512 points) time windows (50% overlapped).For each muscle, the peak RMS value across all MVICtrials represented the maximal EMG activity (RMSMAX).RMSMAX was used to compute the muscle activation level,which is the percentage of EMG amplitude relative to themaximal EMG obtained from largest interexercise MVIC.

The execution of each exercise lasted an average of30 seconds. However, for EMG data analysis just the first20 seconds of activity were considered. This was set tominimize the confounding effect of muscle fatigue on EMGactivation analysis. A standard video camera 30 Hz (Sony)linked to the computer was used to manually synchronizethe recording of both exercise performance and sEMGdata. Thus, one person was filming while another begansignal collection and then the subjects performed theexercise. Subsequently, the video was used to identify thesignal corresponding to the phases of each movement. ForSW, RMS values (250 milliseconds, 50% overlapped)were computed using EMG signals from the concentricback extension phase while lifting the arms and legs. Foreach muscle, the mean RMS value was then computed torepresent the mean RMS activity during the exercise(RMSEXE, EXE = exercise). For SLK, the RMSEXE(r)(r representing the number of repetitions) was computedfor each repetition (lasting 2 seconds on average) from

alternate movements of leg flexion with static backhypertension. For DLK, the RMSEXE(r) was also computedfor each repetition of the simultaneous lifting of the legsand arms with concentric back extension movement. Inboth exercises (SLK and DLK), the RMSEXE(r) values werethen averaged over 5 repetitions to give a single value(RMSEXE(mean of r)). Finally, the activation level (%) wascomputed for each muscle and Pilates exercise using thefollowing equation:

SW:Activation level kð Þ = RMSEXE=RMSMAX × 100kð Þ½ �

SLK and DLK:Acivation level kð Þ = RMSEXEðmean of rÞ=RMSMAX ×100k

� �� :

Statistical AnalysisAll variables were normally distributed, as verified by

the Shapiro-Wilk test. A 2-way repeated measures analysisof variance (2 muscles × 3 Pilates) on the Pilates factor(SW, SLK, and DLK) was performed to assess thedifferences in activation level during the exercises. Posthoc analyses were performed, when necessary, using theTukey test. All statistical analyses were carried out withSPSS 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 musclesranged between 15% and 61% of MVIC among the 3Pilates exercises. No significant interaction (P ≥ .05) wasfound between muscles and Pilates exercises for theactivation level variable (Table 1). In both muscles, SWsignificantly increased muscle activation (29% on average)compared to SLK and DLK (see Table 1). Also, DLKgenerated significantly more activity in the 2 lumbarextensor muscles than did SLK (Table 1). These resultsare further illustrated in Figure 3 with muscle data pooledbecause no significant differences between side muscleswere found during the 3 exercise types (P = .09).

DISCUSSION

The Pilates method has been considered an optimalexercise modality for improving spinal stability as well asthe strength and/or endurance of lumbar muscles.5 Severalstudies12,14,17,18 have investigated the activation of trunkextensor muscles during different modalities of backextension exercises to determine which would best improveback strength and endurance.

However, regarding Pilates exercises, few studies10,11

have assessed the recruitment pattern of trunk musclesduring exercise. Endleman and Critchley10 evaluated trunk

image of Fig 2

Fig 3. Activation level values (error bars correspond to standarddeviations) pooled across muscles during the three Pilatesconditions: SW; SLK, with prone static back extension; andDLK. For more details, see Table 1.

Table 1. Activation values (% MVIC) of the lumbar extensor muscles during mat Pilates exercises

Variable Muscles

Pilates exercises

Muscles

P Analysis of variance

InteractionSW SLK DLK Pilates

Activation (MVIC %) MU-L5-R 61 (21) 19 (11) 47 (21) 0.0091 b.001 0.655MU-L5-L 57 (14) 15 (10) 39 (17) Tukey test results

SW N SLK, DLKDLK N SLK

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 atthe 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).


muscle activity (abdominal only) during traditional andreformer Pilates approaches and only with the use ofultrasound measurements of muscle thickness, which do notcorrespond to the main outcome measure of the presentstudy. Although Petrofsky et al11 observed back extensormuscle activity using EMG, they evaluated Pilates modal-ities (90° and 45° squat, right and left abduction and hipextension) with respect to resistance devices and othermuscle groups, not necessarily targeting back muscles.

To the authors' knowledge, this is the first studycomparing the activity of lumbar muscles during traditionalmat Pilates exercises. Three different mat Pilates exerciseswere assessed: SW, SLK, and DLK. The results of thisstudy demonstrated that a progression of Pilates exercisescan be assigned in order of back muscle activation load.

For example, back activity during SLK was low, onaverage 17% of maximal EMG activity/MVIC (Fig 3), andrelated to static lumbar hyperextension (ie, maintenance of astatic lordotic lumbar posture). In fact, this exerciseemphasizes only an alternating contraction during flexionand extension of legs without overloading the back muscles.

Double leg kick activated the back muscles on average42% of MVIC. This exercise involves intermittent concen-tric action of the trunk muscles with simultaneous back andbilateral leg extension while prone with the hands placedbehind the back. A significant increase in back extensoractivity is observed during prone back extension exerciseswhen the relative trunk load is increased by modifying handand lower limb position.18,19 The effect could be related tothe relative weights of each segment (trunk + legs + arms) onthe rotation axis of the lumbar spine during this exercise.Interestingly, the magnitude of this effect is comparable tothe 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 morelumbar extensor activity (29% on average) than the otherexercises (Fig 3). As stated above, this may be related to loadand moment arm length in this exercise. Generally, morelumbar torque is exerted when a load is positioned furtherfrom the axis of rotation along the moment arm.20

Swimming is performed with dynamic movements, movingthe arms in the extended position and lifting the trunk andlegs during the execution of exercise. Therefore, placingthe hands and arms (part of the torso mass) further awayfrom the axis of rotation of the lumbar spine results in aprogressive increase in back muscle activity, as reported inother studies.12,14,18,19 Plamondon et al18 found a peak levelof 61% of maximum lumbar muscle activity in an exercisesimilar to SW that does not advocate Pilates principles,which agrees with the results of the present study.

Moreover, Sekendiz et al21 showed that Pilates SWexercise was efficient at increasing the strength andendurance of trunk muscles in healthy adult females.Based on our results, the 59% back activation achievedduring this exercise would be sufficient to elicit physiologicchanges and subsequently localize the effects of endurancetraining on the back muscles.

Although several studies have investigated back muscleactivation during a range of back extension exercises suchas specific spinal stabilization exercises,13,14 prone backextension,18,22 roman chair,17,23 and machine-basedexercises,24,25 none used Pilates principles (body align-ment, breathing control, and abdominal control). The

image of Fig 3


results of this study will help in the design of an exerciseprogram specifically for back muscles using a Pilatesapproach. As suggested in a recent review,4 specific backexercises are more efficient for the treatment of LBP. MatPilates work is simpler and more cost-efficient forstrengthening lumbar extensors than exercise usingmachines or dynamometers. However, it is still unclear ifthe Pilates' method provides similar overload stimuluscompared to machines for eliciting strength and endurancegains in back muscles. Further studies are required tocompare the muscle activation in these exercises withdifferent populations and age groups, as well as with otherexercises types (eg, Pilates vs Roman chair and/or Pilates vsmachines). This measure could provide a better under-standing of the effect of exercise on muscle and become aprerequisite for the prescribing of spine stabilization,endurance, or muscular strength training.

LimitationsThis 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 withLBP, who may have different back activation patterns,26,27

nor to male subjects, because some studies have found a sexeffect on back activation.12,28 The activation of abdominalmuscles and hip extensors was not assessed. Furthermore,these results apply only to superficial lumbar muscles seeingthat no deep back muscles were investigated usingintramuscular EMG.

CONCLUSION

The electrical muscle activity of lumbar extensorsranged from 15% to 61% during 3 mat Pilates exercises.In both muscles, the SW exercise significantly increasedmuscle activation (29% on average) relative to the other 2exercise modes. This exercise may be a useful way to focusthe effects of endurance training on the back muscles.

Practical Applications

• The swimming exercise significantly increasedmuscle activation compared to single leg kickand double leg kick.

• The single leg kick is an exercise that empha-sizes only an alternating contraction duringflexion and extension of legs without over-loading the back muscles.

ACKNOWLEDGMENT

The authors wish to thank the Araucaria ResearchFoundation for the fellowship awarded to Rubens A. da

Silva, a visiting Professor and researcher at the Universityinvolved in this study and in the Master of Science inPhysical Education Program, and by the Basic and AppliedResearch Program grant no. 14/08-10069 from theAraucaria Research Foundation.

FUNDING SOURCES AND POTENTIAL CONFLICTS OF INTEREST

No funding sources or conflicts of interest were reportedfor this study.

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