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.