Sensitivity to noxious stimuli is reduced after a single bout of exercise37 but whether this effect occurs after a single session of yoga is unknown. Plausible mechanism for this effect include exercise-induced: (i) reductions in systolic blood pressure (Kelli F.29,49), and (ii) increases in endogenous opioids that could enhance the efficacy of the descending pain modulation system13. The efficacy of this pain processing system is tested in humans using the conditioned pain modulation test54.

Some people engage in yoga to reduce pain. One cross-sectional study of 34,525 adults in the United States found that yoga was practiced to aid back pain by 20% of the sample (H.11). A logical approach to grow knowledge on this topic is to first examine the effects of a single session of yoga. Subsequent research can then more fruitfully examine the time course of repeated acute bouts of yoga. Accordingly, this investigation focused on a single bout of yoga. Reductions in pain sensitivity after a single session of yoga could plausibly result from multiple factors including reductions in systolic blood pressure, greater efficacy of the descending pain modulation system, expectations16, mindfulness35, slow breathing (H.22), and anxiolysis (2; Shirley48).

Yoga is a complex stimulus that includes cognitive strategies (e.g., mindfulness, meditation, relaxation), body postures and breathing patterns. Here we focused on the potential effect of acute yoga postures and changes in breathing frequency on pain processing. Yoga postures could reduce pain sensitivity by acting on the descending pain modulation system or other components of the brain's nociceptive processing system32,43, but whether this is true after a single session of yoga is unexplored.

Slow breathing also can reduce pain responses to standardized noxious stimuli (8; H.24,34), presumably via cognitive variables such as attention to breathing, expectations about slow breathing, mood changes such as reductions in anxiety in response to slow breathing (H.22,55) or increased parasympathetic activity or increased pulmonary afferent input to brain areas involved in voluntary control of breathing (e.g., central amygdala, locus coeruleus)3,6,8,40.

This experiment examined the effect of two yoga components on pain sensitivity and descending pain modulation. Using a post-test only between-subjects design, the effect of a single session of yoga postures, both in one group without slow breathing and in a different group with slow breathing (Vinyasa yoga), on heat pain sensitivity and endogenous pain modulation was examined in a sample of young women. There are a wide variety of yoga styles, and one review of randomized controlled trials (RCTs) found over 53 different styles within the 306 RCTs included in the review12. Our study uses Vinyasa style yoga and a supplemental table outlines the common styles practiced for the sake of easy comparison. Women are the focus of this study because yoga is increasingly popular, especially among women50. The post-test only design avoided the potential artifact resulting from pre-test exposure to noxious stimuli42. Compared to a control condition involving both seated rest and normal breathing, and statistically controlling for four potential confounding variables (i.e., expectations, systolic blood pressure, state anxiety and pain induced by the conditions), reductions in heat pain sensitivity and greater endogenous pain modulation were hypothesized for the main effects of yoga postures and slow breathing as well as the interaction of yoga postures and slow breathing.