Abstract
BackgroundChronic activation of the stress-response can contribute to cardiovascular disease risk, particularly in sedentary individuals. This study investigated the effect of a Bikram yoga intervention on the high frequency power component of heart rate variability (HRV) and associated cardiovascular disease (CVD) risk factors (i.e. additional domains of HRV, hemodynamic, hematologic, anthropometric and body composition outcome measures) in stressed and sedentary adults.MethodsEligible adults were randomized to an experimental group (n = 29) or a no treatment control group (n = 34). Experimental group participants were instructed to attend three to five supervised Bikram yoga classes per week for 16 weeks at local studios. Outcome measures were assessed at baseline (week 0) and completion (week 17).ResultsSixty-three adults (37.2 ± 10.8 years, 79% women) were included in the intention-to-treat analysis. The experimental group attended 27 ± 18 classes. Analyses of covariance revealed no significant change in the high-frequency component of HRV (p = 0.912, partial η2 = 0.000) or in any secondary outcome measure between groups over time. However, regression analyses revealed that higher attendance in the experimental group was associated with significant reductions in diastolic blood pressure (p = 0.039; partial η2 = 0.154), body fat percentage (p = 0.001, partial η2 = 0.379), fat mass (p = 0.003, partial η2 = 0.294) and body mass index (p = 0.05, partial η2 = 0.139).ConclusionsA 16-week Bikram yoga program did not increase the high frequency power component of HRV or any other CVD risk factors investigated. As revealed by post hoc analyses, low adherence likely contributed to the null effects. Future studies are required to address barriers to adherence to better elucidate the dose-response effects of Bikram yoga practice as a medium to lower stress-related CVD risk.Trial registrationRetrospectively registered with Australia New Zealand Clinical Trials Registry ACTRN12616000867493. Registered 04 July 2016.
Highlights
Chronic activation of the stress-response can contribute to cardiovascular disease risk, in sedentary individuals
We hypothesized that participants randomized to the intervention would significantly increase the high frequency (HF) power component and experience significant adaptation of associated cardiovascular disease (CVD) risk factors, including additional heart rate variability (HRV) measures and a range of hemodynamic, hematologic, anthropometric and body composition outcomes compared to a no treatment control
Four participants in the experimental group and one participant from the control group were excluded from analysis post-randomization after recalculation of the 21-item depression-anxiety-stress scale (DASS-21) stress scores
Summary
Chronic activation of the stress-response can contribute to cardiovascular disease risk, in sedentary individuals. This study investigated the effect of a Bikram yoga intervention on the high frequency power component of heart rate variability (HRV) and associated cardiovascular disease (CVD) risk factors (i.e. additional domains of HRV, hemodynamic, hematologic, anthropometric and body composition outcome measures) in stressed and sedentary adults. The sympathetic nervous system (SNS) mediates neuroendocrine changes via the hypothalamic-pituitary-adrenal (HPA) axis [4, 5]. This ‘fight-or-flight’ response includes the release of stress hormones (e.g. cortisol, aldosterone, epinephrine), which in turn increase heart rate, blood pressure, and blood lipid and glucose concentrations, preparing the body for physical exertion. Vagal activity is reflected in the high frequency (HF) spectral power component of HRV [14]
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