Energy cost and METs of individual yoga asanas
Eight studies (3,6,26,30–33,38) evaluated the metabolic cost of various yoga asanas held in traditional Hatha or Bikram yoga (which is based off Hatha asanas). The energy cost and METs of all asanas are summarized in Table 2 and Figure 2. As previously noted, very few asanas were of the intensity to produce a MET value greater than three except Dandayamana-Janushirasana (standing head to knee) (26), Dandayamana-Dhanurasana (standing bow), Trikanasana (triangle) (26), and Tuladandasana (balancing stick) (26) during Bikram yoga. Standing asanas (9,26), for the most part, produced slightly higher average MET values than seated poses (33), as did backward bending poses compared with forward bending postures (i.e., Dhanurasana vs Paschimottanasana or seated wheel compared with forward bend) (3,33). The average METs of supine poses (i.e., Savasana or corpse pose) were comparable with rest (MET value = 1.0 (3,30,31).
Inversion poses including Sirsasana (head stand) did not drastically increase metabolic rate higher than the range of 1.7 to 2.5 METs (6,32). No published studies, however, measured the metabolic cost of some of the more difficult inversions/arm balancing poses, including Bakasana (crow/crane), Eka Pāda Gālavāsana (flying pigeon), and Adho Mukha Vr˙ks˙āsana (hand stand), which produced MET values >3 (Larson-Meyer, unpublished data) in the author’s laboratory.
Cardiorespiratory intensity of yoga
The percentage of actual or estimated HRmax and V˙O2max elicited by yoga practice and/or individual asanas is shown in Table 3 for all studies that provided HR data (6,7,9,13,14,23,26,33,34) and/or measured V˙O2max (7,9,33). The intensity of typical yoga practice was highly variable among studies ranging from 49% (14) to 71% (9) of actual or estimated HRmax and from 12 to 40%V˙O2max. More extreme ranges in HR were found between Wii yoga (40%HRmax) (13) and both Surya Namaskar (80%HRmax) (23) and Bikram yoga (51–90%HRmax) (26). The interpretation of HRmax appears to vary according to asanas and room temperature. V˙O2max estimates are complicated by the aerobic fitness and sex of yoga participants, which ranged from an average of 33 to 35 mL·kg−1·min−1 (7,9) to 42 mL·kg−1·min−1 (6) in female practitioners and 47 m·kg−1·min−1 in male participants (9).
Metabolic cost of yoga relative to walking
In addition to evaluating the energy cost and intensity of yoga, four studies simultaneously compared metabolic cost of yoga practice with that of walking at 2.0 (14), 2.9 (26), 3.0 (14), 3.5 (7), and 4.0 mph (9). As stated in the ACSM guidelines, an adult walking at 3 mph on a flat, hard surface is expected to expend approximately 3.3 METs (16). The METs and intensity as percentage of HRmax or V˙O2max if available are summarized in Table 3. In general, walking at 3 mph produced a similar MET response compared with yoga (14), whereas walking at a faster velocity had a higher metabolic cost (7,9).
Only one study (9) reported the RPE or effort during yoga practice. The RPE according to the Borg scale, which ranges from a value of 6 at rest to 20 at maximal effort, was 14.8 ± 1.8 METs for the aforementioned practice of standing Hatha asanas. This was significantly higher than the average RPE of 12.5 ± 1.5 for treadmill walking at 4 mph for the same subjects, despite the higher MET values elicited for walking (5.4 METs) versus yoga practice (4.1 METs).
Energy cost of pranayama
Five studies (22,26,33,36,38) evaluated the metabolic cost of pranayamas or the controlled and specific breathing patterns/movements commonly practiced in yoga using a ventilated hood (38), a cart with face mask or mouthpiece (26,33,36), or a full-room calorimeter (22). The metabolic cost of pranayamas is summarized in Figure 3. The MET values of the majority of pranayamas were slightly above rest (MET = 1.0), averaging 1.3 ± 0.3 except Yoga Mudra, Kaki Mudra, high-frequency breathing, and standing deep breathing which had METs just higher than 1.5. The metabolic cost of kapalbhati breathing was also slightly higher, but the MET value varied between studies (33,38). Pranayama did not elicit a significant change in HR response in the one study that simultaneously evaluated HR (26), but some such as kapalbhati did elevate ventilation above restful breath (33). High-frequency yogic breathing was found to increase energy expenditure from carbohydrate whereas breath awareness decreased energy expenditure from fat compared with rest, but the RER unfortunately was not reported.
This work is the first to comprehensively review the published literature evaluating the energy cost and intensity of yoga practice, including individual asanas (poses/postures) and pranayamas (breathing exercises). On the basis of the ACSM and the AHA classification systems (2,10,12,16), the intensity of yoga asanas and of full yoga practice ranged from light (less than 3 METs) to moderate (3–6 METs) to vigorous aerobic (>6 METs) with the majority classified as light intensity. The asanas and sequences of asanas that elicited MET intensities in the moderate-intensity aerobic range included Surya Namaskar (sun salutations) and specific standing and balancing postures, including Tuladandasana (balancing stick) and Dandayamana-Dhanurasana (standing bow). This highlights that yoga is not typically practiced at an intensity that meets the ACSM/AHA recommendations for moderate-intensity aerobic exercise (12,16), and it is on average less aerobically intense than brisk walking. In accordance with the guidelines, however, it further highlights that the practice of sequences of asanas with MET intensities higher than 3 METs (i.e., for ~10 min or longer) can be accumulated throughout the day and count toward daily (or weekly) recommendations for moderate- to vigorous-intensity aerobic activity (16).
Energy cost and intensity of yoga practice
Despite a general classification as a light-intensity exercise modality, the findings from this systematic review suggest that the energy cost and MET intensity of a yoga session can be altered according to the asanas practiced and the velocity of flow between asanas (i.e., jump vs slow controlled transitions). Devotion of significant time to Surya Namaskar (7,23,34) and the inclusion of standing and balancing poses that involve isometric contractions with jump transitions between asanas (9) would be expected to increase overall energy cost and intensity of a yoga session (23). Alternatively, the inclusion of more seated versus standing poses with a slower flow through asanas would be expected to decrease energy cost and intensity. Quite surprisingly, this review did not find that environmental (or room) temperature had much effect on energy cost. Despite purported claims that a Bikram yoga session expends up to 1000 kcal in 90 min, the MET values of Bikram yoga (26), performed in hot room with 40% relative humidity, were within the same range as yoga practiced at room temperature. It could be argued, however, that differences might be found if the same practitioners had performed the same set of asanas in both a hot and more ambient environment. Bikram for example does not incorporate Surya Namaskar or flow transitions but instead transitions from static asana to static asana, which may require less energy than other styles with continuous flow through Surya Namaskar and other asanas.
The variability of MET intensities for Surya Namaskar (sun salutations), which ranged from 2.9 METs (light intensity) (14) to 7.4 METs (vigorous intensity), is intriguing. Flow through this specific sequence of 12 asanas, which is performed rhythmically with controlled breath, involves the majority of joints and muscles and both static stretching and dynamic muscular exercise components (34). The sequence is said to be taught to Indian children at young age and is believed to promote cardiorespiratory fitness (23). Interestingly, higher MET intensities (7.4 METs) were observed by Mody (23), who studied five Indian men and women who had trained in Surya Namaskar for at least 2 yr (23). Four rounds of Surya Namaskar were performed at a pace of 3 min per round. Although a sufficient detail on sequence execution was not described, to achieve such high MET intensities, the experienced practitioners most likely incorporated rapid stepping (or jumping) between asanas and an upward and/or downward push-up in Uttihita Chaturanga Dandasana, i.e., flow from plank pose to Bujangasana (cobra pose) and back to plank before moving into Adho Mukha Svasana (down dog). In agreement, a MET intensity of 6.4 was achieved in the author’s laboratory using Mody’s description of Surya Namaskar, transition jumps, and full pushups (Larson-Meyer, unpublished data). By contrast, MET intensities in the moderate-intensity range were observed by both Sinha et al. (34) and Clay et al. (7) in 21 newly trained male practitioners (recently completing three-months of intense training) and 26 semiexperienced female practitioners (minimum of one month of yoga attendance), respectively. The lower MET intensities of Higgins et al. (14) were observed in 18 woman and 2 men who performed 28 min of Surya Namaskar as part of a 56-min beginning-level Ashtanga session. Unfortunately, sufficient information on the Surya Namaskar flow was also not provided (7,14,34), but illustrations in the manuscripts of Sinha et al. (34) matched that of Mody (23), suggesting that the most common variation (Sun salutations A) was used in both studies. Taken together, these findings highlight that Surya Namaskar can be practiced in such a way to achieve an aerobically intense effort but also slowed to result in a light- to moderate-intensity effort.
Influence of practitioner experience
It is not yet established whether practitioner experience affects the metabolic cost of yoga practice, as it does with other types of exercise (1). One could argue on one hand that with consistent practice, yoga participants would learn to more fully express a pose that would in turn result in engagement of more muscle fibers/muscle groups, more forceful contractions of engaged muscles, and deeper movement into each pose. Full expression of many asanas, for example, requires near-maximal contraction of several muscle groups, including the abdominals and back, and an increased range of motion to lift higher or sink deeper into each asana. One could also argue on the other hand that experienced practitioners may have increased flexibility, which could result in reduced passive torque in muscle tissue, reduced resistance to joint movement, and in turn both increased energy efficiency and lowered energy cost (7). Unfortunately, this review found only two studies that directly compared the energy cost of yoga practiced by experienced versus novice practitioners (26,38), one evaluating Bikram practice (26) and the other focused on pranayamas. In the former, the energy cost of a 90-min Bikram yoga session was 27% higher in experienced compared with novice practitioners (4.7 ± 0.8 vs 3.7 ± 0.5 kcal·kg−1). Experienced practitioners also had a 67% greater elevation in core temperature than novice practitioners despite an 83% higher sweat losses alluding to increased work output in experienced practitioners. The pranayama study was in agreement (38). Experienced practitioners were able to substantially increased oxygen cost during breathing exercises compared with novice practitioners despite a lower oxygen cost at rest. Additional research in this area is certainly needed to help establish how experience influences the energy cost of yoga practice.
Cardiorespiratory indicators of yoga intensity
This review further supports that the evaluation of exercise intensity using %HRmax, %V˙O2max, and %HRR—more commonly used for individual exercise prescription (12)—yields results similar to MET intensity. Using these criteria, the majority of studies also found that yoga does not meet the ACSM criteria for moderate-intensity aerobic activity defined as eliciting an HR in the range 64 to 76%HRmax or an oxygen cost between 46 and 63%V˙O2max. The exceptions include Surya Namaskar (7,23,34), standing Iyengar asana practice with jumps between poses (9), and Bikram practice (26). These practices, except the Bikram session, increased MET values to within the moderate-intensity range. The use of absolute or relative (%HRmax) HR, however, may not be an overall valid indicator of exercise intensity during yoga. Several studies found that HR was disproportionally higher than the corresponding oxygen (energy) cost or MET intensity during both Hatha (7,9) and Bikram (26) yoga. For instance, Clay et al. (7) found that a 30-min session at 2.17 METs (15% of V˙O2R) elicited an average HR response of 67% %HRmax, which is considerably higher than expected (see Table 1) (12). HR was also 28 bpm higher during yoga compared with treadmill walking (133 vs 105 bpm) at a higher MET value (3.5 mph, 4.6 METs). Di Carlo et al. (9) observed that standing Hatha yoga induced higher HR and blood pressure responses (71%HRmax) than brisk walking at 4.0 mph at a higher MET intensity of 5.4 METs (62%HRmax). Disproportionally higher HRs during yoga, which integrates arm movements and forceful isometric contractions, however, are expected. These exercise activities alter the hemodynamic and neural responses and elicit a greater HR response than exercises involving leg muscles and dynamic contractions at similar oxygen cost (20). Higher HR values are also expected during yoga practiced in a hot and/or humid environment because of the reactionary shift in blood flow toward the skin, in attempt to maintain thermal homeostasis, which reduces stroke volume and increases HR to maintain cardiac output (20). Similarly, RPE using the Borg scale may also not be a valid indicator of intensity during yoga. The one study that evaluated RPE found that standing Hatha yoga at 4.1 METs elicited an 18% higher RPE than treadmill walking at 5.4 METs (RPE = 14.8 ± 1.8 vs 12.5 ± 1.5) (9).
Quality of measurement of energy expenditure
All studies included in this review used indirect calorimetry to measure oxygen consumption and carbon dioxide production to thereby calculate the energy cost of yoga. Gases were collected using a variety of apparatuses that included a ventilated hood (during pranayamas) (38), mouthpiece and nose clips (26,32), or face mask (13,23,30,31,33), or used a full-room respiratory chamber (14,22). In the one study that evaluated testing reproducibility, the test–retest reliability of the energy cost of yoga measured in the respiratory chamber was sufficiently consistent with an interclass coefficient of 0.97 (14). Although it is tempting to speculate that use of the mouthpiece or mask might induce restraints on a yoga practice, this review found no indication that the gas collection apparatus affected energy cost. Respiratory chambers have the advantage of allowing freedom of movement without restraints of headgear; however, they are expensive, and metabolic carts have been used most commonly to measure the energy cost and MET intensity of most physical activities (1). For example, the energy costs of videotaped yoga sessions averaged 0.63 kcal·kg−1·min−1 using a metabolic cart (7) and 0.58 kcal·kg−1·min−1 when measured inside a respiratory chamber (14). The quality of data collected, however, was difficult to systematically critique because of lack of reported methodological detail. Therefore, this review had to assume that included studies followed standardized procedures, including calibration of gas and volume analyzers, enforced sufficient control of participant’s intake and exercise before testing, and ensured a steady state in oxygen consumption even during the continuous flow through various asanas (7,14,23,27). If oxygen steady state was not achieved, which typically takes at least a minute with continuous exercise, energy cost would be underestimated. To ensure the collection of reliable and accurate metabolic data, future studies should control diet, caffeine, fluid consumption, exercise, sleep, and medications of study participants at least 24-h before measurement.
The benefits of yoga
Placing the findings of the current review into a larger discussion of yoga’s potential benefits requires consideration of both the benefits gained from physical activity of lower cardiovascular intensity and yoga’s potential to improve strength and balance, affect the nervous system, and help control stress (4). The ACSM acknowledges that exercise at a lower intensity reduces sedentary behavior and may provide health benefits for older and unconditioned individuals (2,12,16). Exercise below the moderate-intensity threshold (12), including the practice of yoga and pranayama (19,25,39), has also been shown to improve metabolic markers of chronic disease (i.e., insulin resistance, blood pressure, and lipid profiles) without the corresponding improvements in V˙O2max. In addition, yoga offers an alternative for individuals who cannot engage in traditional forms of physical activity or who prefer light exercise over more intense aerobic exercise. Yoga is perceived to be a gentler form of exercise and may be a more sustainable means of daily practice for individuals with joint problems, rheumatoid arthritis (17), or back pain (24). A recent review found that yoga was superior to other forms of exercise for improving self-reported health status, aerobic fitness, and muscular strength in older adults (28). For instance, 8 wk of yoga participation improved treadmill walking time to fatigue by 3 min (37). Yoga has also been found to benefit those who are more aerobically fit. A study of distance runners found a small but significant improvement in running performance after a single yoga session (11). Similarly, 24 sessions of yoga performed for 8 wk led to improved balance, leg strength, and leg muscle control in young athletes (15). Many of these benefits may be linked to yoga’s ability to increase strength, balance, and flexibility; to calm the mind; and to reduce stress (4). The ACSM position statement for exercise prescription emphasizes that multifaceted physical activities that involve combinations of neuromotor exercise, resistance exercise, and flexibility exercise, which includes yoga, have numerous benefits beyond cardiovascular fitness (12). Results of this study suggest that certain aspects of yoga practice, particularly the more intense asanas, can count toward the weekly amount of physical activity suggested by the ACSM guidelines (16).
Currently, published studies are somewhat limited in that they were conducted mostly in fairly experienced Indian men (23,30–33,35,36) or women practicing in US metropolitan cities (7,14,27) who were relatively young, apparently healthy, and of normal weight. The exception was for the Wii yoga studies that included Japanese and English adolescents and older individuals (13,22). Results are therefore not generalizable to individuals with obesity or adverse health conditions, the elderly, or the young children. The MET intensities included in this review are also only average summaries from included studies, which rarely reported the full range of oxygen uptake and MET intensities. Consequently, the range of energy cost and MET intensities for yoga asanas, pranayama, or full yoga sessions are not available. Regardless, the review provides information for exercise professionals, yoga instructors, health care providers, and yoga practitioners considering practicing yoga as part of physical activity-related goals. It also provides a summary of MET values that may be useful for future MET tables (1) and exercise guidelines. Future studies are needed to better understand how experience and individual variability influence the energy cost and intensity of yoga.
No funding was received for completion of this project. The author declares no conflict of interest. Results of the present study do not constitute endorsement by the American College of Sports Medicine.
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Keywords:© 2016 American College of Sports Medicine
ENERGY EXPENDITURE; YOGA ASANAS; PRANAYAMA; METABOLIC EQUIVALENTS; OXYGEN UPTAKE; EXERCISE INTENSITY