Discussion
This study examined physiological (SBP, HR, and HRV) responses to a vinyasa yoga session compared to a prolonged seated control session. Compared to the seated control condition, vinyasa yoga elicited the hypothesized and favorable BP response by decreasing both SBP and DBP. Contrary to the hypotheses, HR and HRV responses were unexpected compared to the control, with HR increasing, most HRV variables decreasing, and LF/HF ratio slightly increasing at both time points following the yoga condition compared to the control. It is worth noting that even though HR remained above baseline values by 65 minutes post yoga, HR returned clinically near baseline values by the final, 65-minute post measurement (+0.72 bpm). HRV was lower following the yoga condition compared to the control, but this is largely reflected by a significant increase in HRV during the seated control condition.Post yoga BP responses have not been thoroughly studied with a rigorous study design, but our BP results are similar to a recent study; Pina et al., that found non-significant BP decreases following a 60-minute bout of vinyasa yoga compared to baseline values [The BP responses to the seated control were also similar to previous studies. A study by our group found significant BP increases following a sedentary workday [Similar to post yoga BP responses, acute post yoga HR and HRV responses have not been thoroughly studied in large, diverse samples or utilizing standardized yoga protocols (i.e., reporting yoga style, yoga poses, pose duration, and breathing rate). Our HR and HRV responses post yoga were non-significant within subject and mostly unfavorable compared to the seated control. These HRV findings are consistent with a comprehensive review of some acute and long-term yoga interventions where mixed results were observed. As many studies in this review were poor quality with varying yoga intensities [The improved HR/HRV responses to the seated control from this study were not consistent with previous findings. Our group previously performed a meta-analysis of HR/HRV responses to bouts of prolonged sitting and found no significant changes in response to prolonged sitting bouts [There are strengths and limitations to this study. The strengths include consistent visit times, the standardized yoga protocol, the randomized crossover design, an equal number of male and female subjects, measurement of respiration rate during HRV recordings, and a controlled room temperature. Despite these strengths, the limitations of our study should also be addressed. Weaknesses include utilizing a heart rate monitor rather than the gold standard electrocardiogram to measure HRV, studying a single style of yoga (vinyasa), including mostly participants that were meeting physical activity guidelines, a convenient (healthy) sample, and the laboratory setting which, though important for internal validity, may have reduced ecological validity. Further, though we intended our control condition to be a neutral comparison, prolonged sitting resulted in significant changes in our cardiovascular parameters which influence between-condition comparisons. The self-selected deskwork activity chosen for the washout period between post condition measures may also have influenced some of the changes observed in this study. Future studies should seek to recruit a more generalizable sample and investigate the effects of yoga over time in a parallel arm randomized controlled trial study design. Additionally, studies should consider including other yoga styles, other conditions that measure responses to the individual components of vinyasa yoga, comparison to a more neutral control condition or another type of moderate-intensity aerobic exercise, other ANS responses directly quantifying sympathetic activity, and follow-up measurements past 65 minutes following the cessation of exercise.