Yoga is increasingly used in clinical settings for a variety of mental and physical health issues, particularly stress-related illnesses and concerns, and has demonstrated promising efficacy. Yet the ways in which yoga reduces stress remain poorly understood. To examine the empirical evidence regarding the mechanisms through which yoga reduces stress, we conducted a systematic review of the literature, including any yoga intervention that measured stress as a primary dependent variable and tested a mechanism of the relationship with mediation. Our electronic database search yielded 926 abstracts, of which 71 were chosen for further inspection and 5 were selected for the final systematic review. These five studies examined three psychological mechanisms (positive affect, mindfulness and self-compassion) and four biological mechanisms (posterior hypothalamus, interleukin-6, C-reactive protein and cortisol). Positive affect, self-compassion, inhibition of the posterior hypothalamus and salivary cortisol were all shown to mediate the relationship between yoga and stress. It is striking that the literature describing potential mechanisms is growing rapidly, yet only seven mechanisms have been empirically examined; more research is necessary. Also, future research ought to include more rigorous methodology, including sufficient power, study randomisation and appropriate control groups.

We examined motives for adopting and maintaining yoga practice in a national survey of yoga practitioners (360 yoga students, 156 yoga teachers). Both students and teachers adopted yoga practice primarily for exercise and stress relief, but reported many other reasons, including flexibility, getting into shape, and depression/anxiety relief. Over 62 percent of students and 85 percent of teachers reported having changed their primary reason for practicing or discovering other reasons; for both, the top changed primary reason was spirituality. Findings suggest that most initiate yoga practice for exercise and stress relief, but for many, spirituality becomes their primary reason for maintaining practice.

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Context The scientific study of yoga requires rigorous methodology. This review aimed to systematically assess all studies of yoga interventions to: (1) determine yoga intervention characteristics; (2) examine methodologic quality of the subset of RCTs; and (3) explore how well these interventions are reported. Evidence acquisition Searches were conducted through April 2012 in PubMed, PsycInfo, Ageline, and Ovid’s Alternative and Complementary Medicine database using the text term yoga, and through handsearching five journals. Original studies were included if the intervention: (1) consisted of at least one yoga session with some type of health assessment; (2) targeted adults age ≥18 years; (3) was published in an English language peer–reviewed journal; and (4) was available for review. Evidence synthesis Of 3,062 studies identified, 465 studies in 30 countries were included. Analyses were conducted through 2013. Most interventions took place in India (n=228) or the U.S. (n=124), with intensity ranging from a single yoga session up to two sessions per day. Intervention lengths ranged from one session to 2 years. Asanas (poses) were mentioned as yoga components in 369 (79%) interventions, but were either minimally or not at all described in 200 (54%) of these. Most interventions (74%, n=336) did not include home practice. Of the included studies, 151 were RCTs. RCT quality was rated as poor. Conclusions This review highlights the inadequate reporting and methodologic limitations of current yoga intervention research, which limits study interpretation and comparability. Recommendations for future methodology and reporting are discussed.

Objectives Comparison groups are essential for accurate testing and interpretation of yoga intervention trials. However, selecting proper comparison groups is difficult because yoga comprises a very heterogeneous set of practices and its mechanisms of effect have not been conclusively established. Methods We conducted a systematic review of the control and comparison groups used in published randomized controlled trials (RCTs) of yoga. Results We located 128 RCTs that met our inclusion criteria; of these, 65 included only a passive control and 63 included at least one active comparison group. Primary comparison groups were physical exercise (43%), relaxation/meditation (20%), and education (16%). Studies rarely provided a strong rationale for choice of comparison. Considering year of publication, the use of active controls in yoga research appears to be slowly increasing over time. Conclusions Given that yoga has been established as a potentially powerful intervention, future research should use active control groups. Further, care is needed to select comparison conditions that help to isolate the specific mechanisms of yoga’s effects.