Impact of Spinal Flexion and Extension-based Yoga Postures on Autonomic Nervous System Activity in Moderately Experienced Yoga Practitioners: A Randomized Crossover Trial

Background: The autonomic nervous system (ANS) is a complex neural network responsible for maintaining homeostasis through its sympathetic and parasympathetic components. Yoga, an ancient mind-body practice, has been shown to modulate autonomic function, promoting homeostasis. This study aims to comprehensively evaluate the differential impact of spinal flexion and extension-based yoga postures on autonomic modulation in practitioners with at least 2 years of consistent yoga practice. Methods: This randomized crossover trial included 40 participants of both genders who had practiced yoga for at least 2 years, averaging 3-5 sessions per week. Participants were randomly allocated (1:1) into two groups: Group 1 (n = 20) practiced a set of three spinal flexion-based postures (SFP: Halasana, Padahastasana, Shashankasana) on day 1 and three spinal extension-based postures (SEP: Ardhachakrasana, Ushtrasana, Chakrasana) on day 2; Group 2 (N = 20) practiced SEP on day 1 and SFP on day 2. Autonomic function was assessed using heart rate variability (HRV), respiratory rate (RR), galvanic skin resistance (GSR), and electrogastrogram (EGG), which were measured for 5 min at baseline and 5 min postintervention on both days. The data were analyzed based on linear mixed models. Results: Both SFP and SEP interventions resulted in a significant increase in the high-frequency (HF) component of HRV (P < 0.001), indicating parasympathetic predominance immediately postintervention. RR showed a significant increase postintervention (P < 0.001), likely due to the higher energy demands of the postures. No significant changes were observed in GSR for either intervention. EGG recordings indicated a nonsignificant decrease in overall gastric motility postintervention, potentially due to vagal nerve stimulation. Conclusion: Both spinal flexion and extension-based yoga postures enhance parasympathetic activity in moderately experienced practitioners, as evidenced by increased HF HRV. Future research should focus on long-term impact of different yoga postures and employ advanced measurement techniques for greater methodological rigor.