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BACKGROUND: Stress places a metabolic burden on homeostasis and is linked to heightened sympathetic activity, increased energy expenditure and pathology. The yogic state is a hypometabolic state that corresponds with mind-body coherence and reduced stress. This study aimed to investigate metabolic responses to stress and different yoga practices in regular yoga practitioners (YP), non-yoga practitioners (NY) and metabolic syndrome patients (MS). METHODS: YP (n = 16), NY (n = 15) and MS (n = 15) subjects underwent an experimental protocol that comprised of different 5-minute interventions including mental arithmetic stress test (MAST), alternate nostril breathing (ANB), Kapabhati breathing (KB) and meditation (Med) interspersed with 5 minutes of quiet resting (neutral condition (NC)). During the intervention periods continuous body weight adjusted oxygen consumption (VO2ml/min/kg) was measured using open circuit indirect calorimetry with a canopy hood. RESULTS: This is the first study to report oxygen consumption (OC) in yoga practitioners during and after MAST and the first to report both within and between different populations. The results were analysed with SPSS 16 using 3X9 mixed factorial ANOVAs. The single between-subject factor was group (YP, NY and MS), the single within-subject factor was made up of the nine intervention phases (NC1, MAST, NC2, ANB, NC3, KB, NC4, Med, NC5). The results demonstrated that the regular YP group had significantly less OC and greater variability in their OC across all phases compared to the MS group (p = .003) and NY group (p = .01). All groups significantly raised their OC during the mental arithmetic stress, however the MS group had a significantly blunted post-stress recovery whereas the YP group rapidly recovered back to baseline levels with post stress recovery being greater than either the NY group or MS group. CONCLUSIONS: Yoga practitioners have greater metabolic variability compared to non-yoga practitioners and metabolic syndrome patients with reduced oxygen requirements during resting conditions and more rapid post-stress recovery. OC in metabolic syndrome patients displays significantly blunted post-stress recovery demonstrating reduced metabolic resilience. Our results support the findings of previous randomised trials that suggest regular yoga practice may mitigate against the effects of metabolic syndrome. CLINICAL TRIAL NUMBER: ACTRN12614001075673; Date of Registration: 07/10/2014.
Heart Rate Variability (HRV) and respiratory sinus arrhythmia are directly associated with autonomic flexibility, self-regulation and well-being, and inversely associated with physiological stress, psychological stress and pathology. Yoga enhances autonomic activity, mitigates stress and benefits stress-related clinical conditions, yet the relationship between autonomic activity and psychophysiological responses during yoga practices and stressful stimuli has not been widely explored. This experimental study explored the relationship between HRV, mood states and flow experiences in regular yoga practitioners (YP), non-yoga practitioners (NY) and people with metabolic syndrome (MetS), during Mental Arithmetic Stress Test (MAST) and various yoga practices. The study found that the MAST placed a cardio-autonomic burden in all participants with the YP group showing the greatest reactivity and the most rapid recovery, while the MetS group had significantly blunted recovery. The YP group also reported a heightened experience of flow and positive mood states compared to NY and MetS groups as well as having a higher vagal tone during all resting conditions. These results suggest yoga practitioners have a greater homeostatic capacity and autonomic, metabolic and physiological resilience. Further studies are now needed to determine if regular yoga practice may improve autonomic flexibility in non-yoga practitioners and metabolic syndrome patients. Clinical Trial No 'ACTRN 2614001075673'.