A single session of hatha yoga improves stress reactivity and recovery after an acute psychological stress task—A counterbalanced, randomized-crossover trial in healthy individuals
Introduction
The ancient Indian practice of yoga has been adapted to be a mind-body therapy that is of growing popularity in Australia, Europe and North America, with approximately 7–9% of the population reporting participation in Australia and the USA.1, 2, 3 Modern yoga combines body postures, breath control and meditation and is thought to promote physical and mental well-being.4 In the USA National Health Interview Survey, of those who had practiced yoga, most (78%) reported general wellness or disease prevention as the reason for participation.2 Indeed, emerging evidence supports the link between yoga practice and health for many aspects of physical and mental health.5, 6, 7 In particular, several reviews have suggested that yoga practice can have cardiovascular health benefits by modifying specific indices of cardiovascular disease risk, such as glucose tolerance, lipid profile, sympathetic activation, cardiovagal function, etc8, 9, 10; and most recently, a systematic review and meta-analysis found no difference in reduction of cardiovascular risk factors between yoga and walking or cycling.11 Despite this positive weight of evidence, there are very few studies that address the mechanisms through which yoga affects cardiovascular health.
One proposed mechanism for the effects of yoga is by altering the response to and recovery from acute stress. The physiological response to acute stress has been well studied, both for its immediate effects, and for the chronic effects associated with magnitude of the response. Studies have demonstrated that acute emotional stress itself is potentially harmful to cardiac health, with episodes of anger associated with increased risk of myocardial infarction symptoms.12 Furthermore, the chronic effects of acute stress reactivity have been established, with greater reactivity linked to the development of hypertension13 and atherosclerosis14 as a function of repeated exposures. Considering such negative effects associated with acute stress responses, some studies have examined the potential for long-term practice of yoga to reduce stress reactivity; with both 8-weeks of heated hatha yoga15 and 6 months of yoga practice16 found to reduce the physiological reactivity to stress.
The effects of yoga on stress responses may have an acute component as well as a training (chronic) effect. There is strong evidence that an acute exercise bout can reduce the response to, and recovery from a subsequent acute stressor.17, 18 It follows, therefore, that the exercise component of a bout of yoga may act in the same way. Meta-analyses have demonstrated that the strongest effects of exercise are seen at higher intensities (greater than 75% maximal heart rate (HRmax), lasting for at least 20 min), and yoga has been reported to be well below this level of intensity (e.g. ∼50% HRmax).19 It is important to highlight, however, that yoga is different from aerobic exercise in its mind-body emphasis, and, therefore, the breathing and meditation aspects of yoga might also be expected to contribute to the reduction of the response to acute stress. Indeed, investigations have shown that participants exhibited lower stress reactivity (eg., BP, heart rate, immune and emotional responses) after 6–12 weeks of meditation training20, 21, 22, 23; even short-term meditation interventions (3–5 days) have been shown to lower stress perceptions and salivary cortisol (a marker of Hypothalamic Pituitary Adrenal (HPA) activation) reactivity to a stress task.24, 25
Yoga’s acute effects on psychological outcomes are well established, with commonly reported improvements in mood, anxiety and depression.5 These changes have led to insights in neurobiological changes. For example, improvements in mood immediately after yoga have been associated with higher γ-aminobutyric acid (GABA) levels,26 a neurotransmission system that is also linked to acute stress responses.27 To date, the immediate effect of yoga on psychological responses to acute stress has not been investigated, however, given that acute decreases in anxiety are observed after a bout of yoga and long term yoga practice has been shown to reduce performance anxiety28 and increase self-confidence in medical students,29 it is likely that a single session of yoga could improve psychological aspects of the acute stress response.
The aim of this study was to examine the acute effect of a single hatha yoga session on stress responses using a randomized and controlled crossover design. Considering that physiological reactivity to stress has been shown to be diminished after the completion of a short-term mindfulness meditation training and that an acute bout of aerobic exercise is able to reduce cardiovascular stress responses and improve recovery, we hypothesized that one single session of hatha yoga would attenuate physiological reactivity to and accelerate recovery from a mental stressor. The primary outcomes are cardiovascular and cortisol responses to and recovery from acute stress. In addition, we expected that the yoga condition would result in reduced anxiety and increased self-confidence regarding performance of the stress task, which were the secondary outcomes of this study.
Section snippets
Participants
Twenty-four healthy adults (n = 13 male) participated in the present study (mean ± standard deviation [SD] of age 22.9 ± 3.5 years, body mass index 21.7 ± 2.0 kg/m2). Sample size calculations were based on an anticipated effect size of 0.3, smaller than the moderate size seen in the effects of exercise on the response to acute psychological stress,17, 18 and using alpha = 0.05, with 2 interventions repeated measures design (number depending on outcome). Exclusion criteria included a) suffering from an
Cardiovascular reactivity to stress
Data for systolic blood pressure (SBP) and diastolic blood pressure (DBP) are presented in Fig. 1(A) and (B), respectively. There was a significant effect of time for both SBP (F(3.18) = 20.918, p < 0.001, ƞ2 = 0.777) and DBP (F(3.18) = 4.986, p = 0.011, ƞ2 = 0.454), with BP higher at the end of the stress task compared to baseline (p < 0.001). No condition or condition by time effects were found for stress reactivity in SBP or DBP.
Fig. 1(C) and (D) present the summary data for heart rate (HR) and heart rate
Discussion
This study demonstrated, for the first time, that yoga shows acute, ameliorating effects on the stress response. A single hatha yoga session, practiced by healthy individuals before their exposure to an acute stressor, accelerated BP recovery from stress; reduced the magnitude of the HPA axis response, indicated by salivary cortisol; and increased self-confidence in preparation for the task and after completion. Moreover, these results add novel evidence to the literature considering that the
Acknowledgements
CNPq − Brazil Science without Borders Program, which provided funding for M. Benvenutti and E. da Silva Alves to study at the University of Sydney.
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