Muscle Activity during Yoga Breathing Exercise Compared to

The Journal of Applied Research • Vol. 5, No. 3, 2005 501

Muscle Activity during YogaBreathing Exercise Compared toAbdominal CrunchesJerrold S. Petrofsky, PhD*Maria Cuneo, MPT*Russell Dial, MPT*Amy Morris, BS†

*Department of Physical Therapy, Loma Linda University, Loma Linda, California†Department of Physical Therapy, Azusa Pacific University, Azusa, California

INTRODUCTIONYoga, which is commonly used for mus-cle relaxation,1 can be performed bymost people, including young peopleand cardiac patients.2-5 It has been usedto build core stability during and afterpregnancy6 and has been shown toincrease creativity and reduce stress,7 aswell as to improve muscle power, dex-terity, visual perception,8 and reactiontime.9 However, while strength,endurance, and muscle reaction timeshave been previously quantified, littlehas been done to quantify muscle useduring yoga through the use of the elec-tromyogram (EMG).10,11

The EMG, when measured by sur-face electrodes above an active muscle,represents an interference pattern giv-ing the summation of activity of theunderlying muscle fibers.12 The ampli-tude of the surface EMG is generallyrelated to the tension developed inmuscle.12,13 Therefore, the EMG hasproved to be a useful measure in assess-ing both the extent of muscle activityand muscle fatigue.12-17

While some investigators find somevariation in the EMG tension relation-ship due to the type of electrode (nee-dle or surface) or the size or position ofthe electrodes,18,19 if the EMG is nor-

KEY WO R D S : y o g a , r e l a x a t i o n , s t r e s sm a n a g e m e n t , p o s t u r e

ABSTRACTYoga and yoga-related training haveoften been touted as providing goodmuscle stretching and relaxation, as wellas being beneficial for overall stressmanagement. During forceful musclecontractions of yoga, substantial muscleactivity can be demonstrated. In thepresent investigation, the muscle activityof the right and left rectus abdominisand of the right and left external obliquemuscles was examined to assess the levelof muscle activity during one type ofyoga maneuver: a breathing exerciseperformed in the seated position. Theresults showed that while muscle activityduring this yoga breathing exercise wascomparable to that seen during the per-formance of abdominal crunches, thelonger duration of the breathing exercis-es increased the total work on theabdominal muscles up to 5 times greaterthan the work during crunches. Becauseof the high muscle activity, this form ofexercise would be good for people whocannot easily exercise on the floor suchas people with disabilities or obese people.

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Vol. 5, No. 3, 2005 • The Journal of Applied Research502

malized as a percent of the muscle’smaximum EMG during a maximumstrength measurement, the EMG is areliable tool to measure muscle use.16,17

This paper uses the EMG to quanti-fy abdominal muscle activity duringabdominal yoga exercises versus tradi-tional curls to understand the magnitudeof muscle use associated with yoga. Thisis particularly important since yoga hasbeen reported to increase musclestrength and the strength of respiratorymuscles (including the obliques and rec-tus abdominis muscles).8

MATERIALS AND METHODSSubjectsTwenty-nine subjects (14 male and 15

female) aged 17 to 49 years participatedin this study. The general characteristicsof the subjects are shown in Table 1. Allexperimental protocols and procedureswere approved by the Human ReviewCommittee at Azusa Pacific Universityand all subjects signed a statement ofinformed consent acknowledging thatthey are fully aware of the purposes andprocedures of the project.

ElectromyogramThe EMG was recorded through 2 bipo-lar vinyl adhesive electrodes (silver sil-ver-chloride) with an active surface areaof 0.5 cm2. One electrode was placedover the belly of the active muscle. Thesecond electrode was placed 2 cm distal

Figure 1. Subject performing abdominal crunch

Table 1. General Characteristics of Subjects

Age (years) Weight (kg) Height (cm)Mean ± SD 38.3 ± 13.4 73.3 ± 15.3 167.3 ± 11.8



to the active electrode. EMG wasamplified using a 4-channel EMG ampli-fier whose frequency response was flatfrom DC to 1000 Hz. The commonmode rejection ratio of the amplifierwas greater than 120 Db. The EMG wasdigitized at 1,000 samples/sec by aBiopac (Biopac Corp., Santa Barbara,CA) 16-bit analog-to-digital converterand displayed and stored on a computerfor later analysis. The amplitude ofEMG was assessed by digitizing and halfwave rectified the raw EMG and calcu-lating the root mean square average(RMS) of the EMG.

Measurement of Strength of theAbdominal MusclesIsometric strength of the abdominalmuscles was measured in the seatedposition. To accomplish this, subjects satwith the hips at an angle of 90º. A modi-fied exercise device with strain gaugeswas used to assess maximum strength.The strain gauge was linear from 0-200 kg of force. The output of thetransducer was amplified with a straingauge conditioner amplifier with a gainof 1000 and digitized in a Biopac 16-bitanalog-to-digital converter and dis-played and stored on a computer. The

Figure 2. Average muscle activity of the (A) left and (B) right obliques and (C) left and (D) rightrectus abdominis muscles during each of the two conditions. Each panel shows EMG activityexpressed as a percent of the EMG during the maximum strength determinations. Yoga breath-ing exercise is compared to abdominal crunches lying supine on the floor. All data are themean result for the entire group ± the respective SD.



output was stored and analyzed as theaverage strength over the middle of a 3-second contraction. Strength wasmeasured by an isometric contractionfor 3 seconds. At least 1 minute wasallowed between each of 3 contractionsto allow for recovery.

Breathing ExerciseMuscle activity was examined duringYoga deep breathing exercise performedin the seated position. The breathingexercise involved slowly exhalingthrough the mouth and then rapidlyinhaling through the nose to fullyexpand the lungs. Next the air wasexhaled through the mouth rapidly usingthe abdominal muscles and thediaphragm as much as possible. Withthe air exhaled, the mouth is kept closed

and a maximum contraction was accom-plished with the abdominal musclesagainst a closed glottis. This last positionwas held for an average of 6 seconds.

ProceduresTwo series of experiments were per-formed. In the first, conventionalabdominal crunches were accomplishedby having the subjects lay supine on thefloor and contract the abdominal mus-cles to bring the elbows and head to aposition to where the shoulders justcleared the floor (Figure 1). The armswere folded on the chest. EMG was thenmeasured during this activity. A yogabreathing exercise was then performedin the seated position as described undermethods, during the contraction, EMGwas also measured. To normalize the

Figure 3. Work of the (A) left obliques, (B) right obliques, (C) left rectus abdominis, and (D) rightrectus abdominis during breathing compared to work during supine abdominal crunches. Workis calculated as the product of muscle activity ¥ the duration of the exercise. Since muscleactivity is normalized to each person, it is in relative units.



EMG on both sets of experimental con-ditions, the maximum strength wasdetermined for the abdominal muscleswhile sitting and with forward flexionfor the rectus abdominis muscles andduring rotation to the left and right toobtain maximum use of the obliques.

Statistical AnalysisStatistical analysis involved the calcula-tions of mean standard deviations and t-tests. The level of significance wasP<0.05.

RESULTSThe results are shown in Figures 2 and 3.As shown, muscle activity for all 4 mus-cle groups during abdominal crunchesaveraged 24% of the total activity ofthese muscles. For breathing exercises,muscle activity was somewhat greaterwith 41% of the muscle activity. Thesedifferences were significant (P<0.05).For breathing exercises, the greatestmuscle activity was for the obliques.Here activity was almost double that ofthe rectus abdominis muscles. In con-trast, for crunches, the greatest activitywas for the rectus abdominis muscles.Although the muscle activity was similarfor the two exercises, there was a differ-ence: the duration of the exercise waslonger for the breathing exercises. Thesubjects had an average duration of 2.1± 0.8 sec for the crunches. In contrast,for yoga exercise, the average durationwas 5.09 ± 2.1 sec; these differenceswere significant (P<0.01).

By multiplying the product of theduration of the exercise by the EMGlevels, the workload, as shown in Figure3, was significantly higher (P<0.01) foryoga exercises compared to standardabdominal crunches. The work for theobliques was over twice as high as thatof the rectus abdominis muscles. Thetotal work, adding all muscles togetherwas 803 for the breathing exercises and166 for the crunches. With yoga, the

work for each muscle group and thetotal work were higher than that seenwith crunches (P<0.01). Thus the workperformed in a single breathing exercisewas equivalent to 5 crunches. For therectus abdominis, the work was about2.5 times higher in the breathing exercis-es than for the crunches, whereas for theobliques, the work was 6 times higherthan for the crunches.

DISCUSSIONIt is known that yoga is a good trainingtechnique for muscle relaxation.20 Froma psychological standpoint, it alsoreduces anxiety.20 But yoga also hasbeen shown to decrease neurologicalreaction time and improve musclestrength and endurance of the expirato-ry and abdominal muscles.9 This, then,has important benefits in terms of expi-ratory disorders such as asthma.21,22 Foryoga, if there is increased muscle powerand muscle dexterity, then the exerciseitself must be using appreciable musclestrength.8 This is especially true forwomen who wish to build core stabilityduring and after pregnancy.6 In thepresent investigation, considerable mus-cle activity was found for the rectusabdominis and exterior oblique musclesduring yoga exercise involving the coremuscles of the body.

Studies show that strengthening ofthe core muscles with sit-ups or othertypes of abdominal exercise contributesto increased functional abilities.23,24

When the abdominals and lower backmuscles are strengthened using exercisemachines, bowel and bladder programsin rehabilitation or health centers havebeen shown to be more effective.25

Further, if individuals are prone tofalling, increasing core muscle stabilityincreases the person’s ability to maintainbalance while reaching.23,24 Thus, exerciseof the core muscles26-29 increases overallaerobic capacity and improves stabilityof the upper and lower body through

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training of the erector spinae, transver-sus abdominus and rectus abdominusmuscles, resulting in improved therapeu-tic reach and balance, better breathing,and better activity of the bowel.

One particularly interesting findingof this investigation was the fact thateven for the rectus abdominus muscle,which is somewhat active during abdom-inal crunches, the total muscle activitywas substantially higher during the yogabreathing exercises than during the stan-dard abdominal crunches. In theoblique muscles, which are used mini-mally during abdominal crunch exercis-es, yoga breathing exercises causeconsiderably more work in these mus-cles. Thus, yoga breathing is not onlyefficient when exercising the rectusabdominis but it also provides a goodworkout for the oblique muscles as well.If, for example, a yoga breathing work-out were to continue for 20 breaths, thiswould be equivalent to 100 conventionalcrunches in abdominal work performed.

Abdominal crunches are usuallyconsidered the gold standard and usedquite commonly during exercise in mili-tary programs and civilian fitness pro-grams. However, yoga breathingexercises, in contrast, are used less fre-quently but workloads are much higher.Therefore, yoga breathing exercises,when combined with other exercisemodalities, provide a much better work-out for the core muscles in the body.Considering the abdominal work withyoga breathing exercises, total bodyworkouts would be much more timeefficient if yoga breathing exercises werecombined and interlaced with otherexercise modalities for a more efficientfitness program. Finally, since breathingexercises can be accomplished from theseated position, yoga is more approach-able and compliance will be better forpeople who have difficulty working in asupine position such as the elderly anddisabled or people with obesity.

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Muscle Activity during Yoga Breathing Exercise Compared to

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