Muscle Activity during Yoga
Breathing Exercise Compared to
Jerrold 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
KEY WORDS: yoga, relaxation, stress INTRODUCTION
management, posture Yoga, which is commonly used for mus-
cle relaxation,1 can be performed by
most people, including young people
ABSTRACT and cardiac patients.2-5 It has been used
Yoga and yoga-related training have to build core stability during and after
often been touted as providing good pregnancy6 and has been shown to
muscle stretching and relaxation, as well increase creativity and reduce stress,7 as
as being beneficial for overall stress well as to improve muscle power, dex-
management. During forceful muscle terity, visual perception,8 and reaction
contractions of yoga, substantial muscle time.9 However, while strength,
activity can be demonstrated. In the endurance, and muscle reaction times
present investigation, the muscle activity have been previously quantified, little
of the right and left rectus abdominis has been done to quantify muscle use
and of the right and left external oblique during yoga through the use of the elec-
muscles was examined to assess the level tromyogram (EMG).10,11
of muscle activity during one type of The EMG, when measured by sur-
yoga maneuver: a breathing exercise face electrodes above an active muscle,
performed in the seated position. The represents an interference pattern giv-
results showed that while muscle activity ing the summation of activity of the
during this yoga breathing exercise was underlying muscle fibers.12 The ampli-
comparable to that seen during the per- tude of the surface EMG is generally
formance of abdominal crunches, the related to the tension developed in
longer duration of the breathing exercis- muscle.12,13 Therefore, the EMG has
es increased the total work on the proved to be a useful measure in assess-
abdominal muscles up to 5 times greater ing both the extent of muscle activity
than the work during crunches. Because and muscle fatigue.12-17
of the high muscle activity, this form of While some investigators find some
exercise would be good for people who variation in the EMG tension relation-
cannot easily exercise on the floor such ship due to the type of electrode (nee-
as people with disabilities or obese dle or surface) or the size or position of
people. the electrodes,18,19 if the EMG is nor-
The Journal of Applied Research • Vol. 5, No. 3, 2005 501
Figure 1. Subject performing abdominal crunch
malized as a percent of the muscle’s female) aged 17 to 49 years participated
maximum EMG during a maximum in this study. The general characteristics
strength measurement, the EMG is a of the subjects are shown in Table 1. All
reliable tool to measure muscle use.16,17 experimental protocols and procedures
This paper uses the EMG to quanti- were approved by the Human Review
fy abdominal muscle activity during Committee at Azusa Pacific University
abdominal yoga exercises versus tradi- and all subjects signed a statement of
tional curls to understand the magnitude informed consent acknowledging that
of muscle use associated with yoga. This they are fully aware of the purposes and
is particularly important since yoga has procedures of the project.
been reported to increase muscle
strength and the strength of respiratory Electromyogram
muscles (including the obliques and rec- The EMG was recorded through 2 bipo-
tus abdominis muscles).8 lar vinyl adhesive electrodes (silver sil-
ver-chloride) with an active surface area
MATERIALS AND METHODS of 0.5 cm2. One electrode was placed
Subjects over the belly of the active muscle. The
Twenty-nine subjects (14 male and 15 second electrode was placed 2 cm distal
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
502 Vol. 5, No. 3, 2005 • The Journal of Applied Research
Figure 2. Average muscle activity of the (A) left and (B) right obliques and (C) left and (D) right
rectus abdominis muscles during each of the two conditions. Each panel shows EMG activity
expressed 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 the
mean result for the entire group ± the respective SD.
to the active electrode. EMG was Measurement of Strength of the
amplified using a 4-channel EMG ampli- Abdominal Muscles
fier whose frequency response was flat Isometric strength of the abdominal
from DC to 1000 Hz. The common muscles was measured in the seated
mode rejection ratio of the amplifier position. To accomplish this, subjects sat
was greater than 120 Db. The EMG was with the hips at an angle of 90º. A modi-
digitized at 1,000 samples/sec by a fied exercise device with strain gauges
Biopac (Biopac Corp., Santa Barbara, was used to assess maximum strength.
CA) 16-bit analog-to-digital converter The strain gauge was linear from
and displayed and stored on a computer 0-200 kg of force. The output of the
for later analysis. The amplitude of transducer was amplified with a strain
EMG was assessed by digitizing and half gauge conditioner amplifier with a gain
wave rectified the raw EMG and calcu- of 1000 and digitized in a Biopac 16-bit
lating the root mean square average analog-to-digital converter and dis-
(RMS) of the EMG. played and stored on a computer. The
The Journal of Applied Research • Vol. 5, No. 3, 2005 503
Figure 3. Work of the (A) left obliques, (B) right obliques, (C) left rectus abdominis, and (D) right
rectus abdominis during breathing compared to work during supine abdominal crunches. Work
is calculated as the product of muscle activity ¥ the duration of the exercise. Since muscle
activity is normalized to each person, it is in relative units.
output was stored and analyzed as the and a maximum contraction was accom-
average strength over the middle of a plished with the abdominal muscles
3-second contraction. Strength was against a closed glottis. This last position
measured by an isometric contraction was held for an average of 6 seconds.
for 3 seconds. At least 1 minute was
allowed between each of 3 contractions Procedures
to allow for recovery. Two series of experiments were per-
formed. In the first, conventional
Breathing Exercise abdominal crunches were accomplished
Muscle activity was examined during by having the subjects lay supine on the
Yoga deep breathing exercise performed floor and contract the abdominal mus-
in the seated position. The breathing cles to bring the elbows and head to a
exercise involved slowly exhaling position to where the shoulders just
through the mouth and then rapidly cleared the floor (Figure 1). The arms
inhaling through the nose to fully were folded on the chest. EMG was then
expand the lungs. Next the air was measured during this activity. A yoga
exhaled through the mouth rapidly using breathing exercise was then performed
the abdominal muscles and the in the seated position as described under
diaphragm as much as possible. With methods, during the contraction, EMG
the air exhaled, the mouth is kept closed was also measured. To normalize the
504 Vol. 5, No. 3, 2005 • The Journal of Applied Research
EMG on both sets of experimental con- work for each muscle group and the
ditions, the maximum strength was total work were higher than that seen
determined for the abdominal muscles with crunches (P<0.01). Thus the work
while sitting and with forward flexion performed in a single breathing exercise
for the rectus abdominis muscles and was equivalent to 5 crunches. For the
during rotation to the left and right to rectus abdominis, the work was about
obtain maximum use of the obliques. 2.5 times higher in the breathing exercis-
es than for the crunches, whereas for the
Statistical Analysis obliques, the work was 6 times higher
Statistical analysis involved the calcula- than for the crunches.
tions of mean standard deviations and
t-tests. The level of significance was DISCUSSION
P<0.05. It is known that yoga is a good training
technique for muscle relaxation.20 From
RESULTS a psychological standpoint, it also
The results are shown in Figures 2 and 3. reduces anxiety.20 But yoga also has
As shown, muscle activity for all 4 mus- been shown to decrease neurological
cle groups during abdominal crunches reaction time and improve muscle
averaged 24% of the total activity of strength and endurance of the expirato-
these muscles. For breathing exercises, ry and abdominal muscles.9 This, then,
muscle activity was somewhat greater has important benefits in terms of expi-
with 41% of the muscle activity. These ratory disorders such as asthma.21,22 For
differences were significant (P<0.05). yoga, if there is increased muscle power
For breathing exercises, the greatest and muscle dexterity, then the exercise
muscle activity was for the obliques. itself must be using appreciable muscle
Here activity was almost double that of strength.8 This is especially true for
the rectus abdominis muscles. In con- women who wish to build core stability
trast, for crunches, the greatest activity during and after pregnancy.6 In the
was for the rectus abdominis muscles. present investigation, considerable mus-
Although the muscle activity was similar cle activity was found for the rectus
for the two exercises, there was a differ- abdominis and exterior oblique muscles
ence: the duration of the exercise was during yoga exercise involving the core
longer for the breathing exercises. The muscles of the body.
subjects had an average duration of 2.1 Studies show that strengthening of
± 0.8 sec for the crunches. In contrast, the core muscles with sit-ups or other
for yoga exercise, the average duration types of abdominal exercise contributes
was 5.09 ± 2.1 sec; these differences to increased functional abilities.23,24
were significant (P<0.01). When the abdominals and lower back
By multiplying the product of the muscles are strengthened using exercise
duration of the exercise by the EMG machines, bowel and bladder programs
levels, the workload, as shown in Figure in rehabilitation or health centers have
3, was significantly higher (P<0.01) for been shown to be more effective.25
yoga exercises compared to standard Further, if individuals are prone to
abdominal crunches. The work for the falling, increasing core muscle stability
obliques was over twice as high as that increases the person’s ability to maintain
of the rectus abdominis muscles. The balance while reaching.23,24 Thus, exercise
total work, adding all muscles together of the core muscles26-29 increases overall
was 803 for the breathing exercises and aerobic capacity and improves stability
166 for the crunches. With yoga, the of the upper and lower body through
The Journal of Applied Research • Vol. 5, No. 3, 2005 505
training of the erector spinae, transver- REFERENCES
sus abdominus and rectus abdominus 1. Ghoncheh S, Smith JC. Progressive muscle
muscles, resulting in improved therapeu- relaxation, yoga stretching, and ABC relax-
tic reach and balance, better breathing, ation theory. J Clin Psychol. 2004;60:131-136.
and better activity of the bowel. 2. Ades PA, Savage PD, Cress ME, et al.
Resistance training on physical performance
One particularly interesting finding in disabled older female cardiac patients. Med
of this investigation was the fact that Sci Sports Exerc. 2003;35:1265-1270.
even for the rectus abdominus muscle, 3. Tran M, Holly R, Lashbrook J, Amsterdam E.
which is somewhat active during abdom- Effects of Yoga practice on the health-related
inal crunches, the total muscle activity aspects of physical fitness. Prevent Cardiol.
was substantially higher during the yoga
breathing exercises than during the stan- 4. Raub J. Psychophysiologic effects of Hatha
yoga on musculoskeletal and cardiopul-
dard abdominal crunches. In the monary function: a literature review. J Altern
oblique muscles, which are used mini- Complement Med. 2002;8:797-812.
mally during abdominal crunch exercis- 5. Dash M, Telles S. Improvement in hand grip
es, yoga breathing exercises cause strength in normal volunteers and rheuma-
toid arthritis patients following yoga training.
considerably more work in these mus- Indian J Physiol Pharmacol. 2001;45:355-360.
cles. Thus, yoga breathing is not only
6. Berk B. Yoga for moms. Building core stabili-
efficient when exercising the rectus ty before, during and after pregnancy.
abdominis but it also provides a good Midwifery Today Int Midwife. 2001;59:27-29.
workout for the oblique muscles as well. 7. Khasky AD, Smith JC. Stress, relaxation
If, for example, a yoga breathing work- states, and creativity. Percept Mot Skills.
out were to continue for 20 breaths, this 1999;88:409-416.
would be equivalent to 100 conventional 8. Raghuraj P, Telles S. Muscle power, dexterity
skill and visual perception in community
crunches in abdominal work performed. home girls trained in yoga or sports and in
Abdominal crunches are usually regular school girls. Indian J Physiol
considered the gold standard and used Pharmacol. 1997;41:409-415.
quite commonly during exercise in mili- 9. Madanmohan, Thombre DP, Balakumar B, et
tary programs and civilian fitness pro- al. Effect of yoga training on reaction time,
respiratory endurance and muscle strength.
grams. However, yoga breathing Indian J Physiol Pharmacol. 1993;36:229-233.
exercises, in contrast, are used less fre-
10. Narayan R, Kamat A, Khanolkar M, et al.
quently but workloads are much higher. Quantitative evaluation of muscle relaxation
Therefore, yoga breathing exercises, induced by Kundalini yoga with the help of
when combined with other exercise EMG integrator. Indian J Physiol Pharmacol.
modalities, provide a much better work-
11. Dostalek C, Faber J, Krasa H, et al. Yoga
out for the core muscles in the body. meditation effect on the EEG and EMG
Considering the abdominal work with activity. Act Nerv Super (Praha).
yoga breathing exercises, total body 1979;21(1):41.
workouts would be much more time 12. Petrofsky JS, Lind AR. The influence of tem-
efficient if yoga breathing exercises were perature on the amplitude and frequency
components of the EMG during brief and
combined and interlaced with other sustained isometric contractions. Eur J Appl
exercise modalities for a more efficient Physiol. 1980;44:198-200.
fitness program. Finally, since breathing 13. Petrofsky JS, Laymon M. The influence of
exercises can be accomplished from the intramuscular temperature on surface EMG
seated position, yoga is more approach- variables during isometric contractions. Basic
Appl Myology. 2005:15;61-74.
able and compliance will be better for
14. Bigland B, Lippold O. The relation between
people who have difficulty working in a force, velocity and integrated EMG. J
supine position such as the elderly and Physiol. 1954;123:214-224.
disabled or people with obesity.
506 Vol. 5, No. 3, 2005 • The Journal of Applied Research
15. Dahms TE, Petrofsky JS, Lind AR. 22. Freedberg PD, Hoffman LA, Light WC,
Relationship between blood flow and muscle Kreps MK. Effect of progressive muscle
tension at low levels of muscular perform- relaxation on the objective symptoms and
ance. Fed Proc. 1975;34:370. subject response associated with asthma.
Heart Lung, 1987;16:24-30.
16. Lindstrom L, Magnusson R, Petersen I.
Muscular fatigue and action potential con- 23. Seelen HA, Potten YJ, Drukker J, et al.
duction velocity changes studied with fre- Development of new muscle synergies in pos-
quency analysis of EMG signals. tural control in spinal cord injured subjects. J
Electromyography. 1970;10:341-356. Electromyogr Kinesiol. 1998;8:23-34.
17. Karlsson S, Gerdle B. Mean frequency and 24. Chen CL, Yeung KT, Bih LI, et al. The rela-
signal amplitude of the surface EMG of the tionship between sitting stability and func-
quadriceps muscles increase with increasing tional performance in patients with
torque—a study using the continuous wavelet paraplegia. Arch Phys Med Rehabil.
transform. J Electromyogr Kinesiol. 2003;84:1276-1281.
25. Ryerson S. Chapter 22: Hemiplegia resulting
18. Alon G. High voltage stimulation. Effects of from vascular insult and disease. In:
electrode size on basic excitatory responses. Umphred D, ed. Neurological Rehabilitation.
Phys Ther. 1985;65:890-895. St. Louis: Mosby Inc; 1995.
19. Alon G, Kantor G, Ho HS. Effects of elec- 26. Dionne I, Johnson M, White MD, et al. Acute
trode size on basic excitatory responses and effect of exercise and low-fat diet on energy
on selected stimulus parameters. J Orthop balance in heavy men. Int J Obes Relat Metab
Sports Phys Ther. 1994;20:29-35. Disord. 1997;21:413-416.
20. Platania-Solazzo A, Field TM, Blank J, et al. 27. Martin B, Robinson S, Robertshaw D.
Relaxation therapy reduces anxiety in child Influence of diet on leg uptake of glucose
and adolescent psychiatric patients. Acta during heavy exercise. Am J Clin Nutr.
Paedopsychiatr. 1992;55:115-120. 1978;31:62-67.
21. Vandevenne A. Respiratory re-training in 28. Pacy PJ, Barton N, Webster JD, Garrow JS.
asthma. Theoretical basis and results. Rev Mal The energy cost of aerobic exercise in fed and
Respir. 1995;12:241-256. [in French] fasted normal subjects. Am J Clin Nutr.
29. Astrand PO, Rodhal K. Physiology of Work
Capacity and Fatigue. New York: McGraw
The Journal of Applied Research • Vol. 5, No. 3, 2005 507