Finding the BalanceWithin: The Effects of Ashtanga Yoga and Cardiovascular Exercise on Autonomic Responses to Psychological and Physical Stressors.

Abstract

The regular practice of yoga has been reliably associated with wide-ranging benefits that are both physical and psychological in nature, and is increasingly recommended as a safe and cost effective adjunct to traditional care for a range of clinical conditions, and effective self-care practice. However, the mechanisms by which yoga may benefit health are poorly understood at present. The present study proposed that the improvements documented as a result of yoga on diverse outcome measures may be attributed to change in underlying nervous system dynamics, in particular, to increased activation of its parasympathetic branch. As increased parasympathetic function is associated with improved cardio-vagal regulatory capacity, the present study investigated changes in autonomic arousal levels among regular Ashtanga yoga practitioners (n = 17) across both a physical stressor task, and a psychological stressor task, which has been shown to engage cortical regions critical for the appropriate matching of arousal levels to situational demands. Autonomic change among yoga practitioners were compared to both a group of superior cardiovascular fitness (n =21), and a group of metabolically matched controls (n =19). Although all groups showed a comparable pattern of heart rate response across task conditions, subtle differences emerged in the way in which these changes were achieved. While cardiovascular fitness was associated with a pattern of vagal withdrawal and recovery in response to the cognitive stressor task, yoga participants showed no change in vagal activity in response to psychological stress, despite their higher levels of overall vagal activity relative to all other groups. This was accompanied by improved regulation in response to the physical task among the yoga group. Control participants, in contrast, showed apparent autonomic dysregulation, with minimal change in vagal activity across all conditions. Results support the hypothesis that yoga fine-tunes underlying nervous system dynamics, and improves function of both top-down and bottom-up vagal circuits. The study demonstrates that at least part of the autonomic benefits that are widely acknowledged as a consequence of cardiovascular exercise may be obtained at a lower intensity through the practice of Ashtanga yoga, as well as highlighting relevance of this ancient practice for promoting autonomic balance amidst that stressors which increasingly characterize contemporary life.