I appreciate the interest in my recently published systematic review of the energy cost of yoga (2) and welcome the opportunity to reply to concerns expressed by Sherman et al. (8). This systematic review included 17 identified articles, dating from 1963 to 2015, that measured the energy expenditure of yoga practice via indirect calorimetry. Of the 17 articles, four measured full yoga sessions, three of which included Surya Namaskar, that is, the “sun salutations,” and one which measured Surya Namaskar exclusively. Surya Namaskar was included in Figure 1 because it involves flowing through a sequence of 12 poses that typically last longer than holding single asanas. Several rounds of Surya Namaskar are commonly incorporated into yoga classes and, according to Mody (4), are practiced by East Indians as part of their physical activity regimen (where one round is completed 12 times). Retrospectively, summarizing the MET intensity of Surya Namaskar in a separate figure may have clarified the concern; however, Surya Namaskar was included in Figure 1 to emphasize that its practice for 10 min at >3 METs counts toward the recommended 30 min of daily physical activity. The study by Dicarlo et al. (1) of Iyengar-style standing poses—that incorporate a series of isometrically held standing postures—was included in Figure 1 for similar reasoning. Although Iyengar yoga sessions also include seated poses and pranayama, standing poses constitute a significant portion of the typical class.
Hatha yoga is performed by assuming standard poses with focus on form and breath. Although routines consist of combinations of standing, seated, and inverted postures, class sequences come in different formats. According to the Yoga Journal, every contemporary school, including Iyengar, Bikram, Ashtanga, and vinyasa, has its own idea of how to sequence a practice (6). Most sequences are linear, such that one posture follows another in a step-by-step direction that moves from less challenging to more challenging and back to less challenging (6). Most traditionally trained yoga instructors would not string a sequence based only on MET values.
With that said, however, many higher MET poses are sequenced together in the 26 Bikram postures (5) and may be sequenced in close proximity to Surya Namaskar in vinyasa and other yoga styles.
Caution should always be taken when recommending any type of exercise to clients exclusively for weight reduction. Increasing “exercise” alone without diet or other lifestyle changes does not necessarily result in weight loss (3). In fact, the weight loss benefits of yoga are likely due to behavioral and/or psychosocial effects that promote healthy, more mindful eating (7). Such discussion was beyond that of the systematic review (2).
It is agreed that additional, well-designed studies are needed to quantify energy cost of full yoga sessions. Details concerning the full sessions included in the review are summarized in Table 3 and defined in the original references. Future studies should focus on evaluating traditional yoga sessions and emerging hybrid forms, including YogaFit and Hot Power yoga.
The current systematic review (2) provides a starting point and demonstrates ranges of MET intensities for yoga practiced in India, the United States, and several European Countries.