Beneficial Effects of Yoga Stretching on Salivary Stress Hormones and Parasympathetic Nerve Activity

In summary, the study found “that salivary cortisol concentration decreased and testosterone/cortisol ratio increased after yoga stretching.” And that a major finding of this study, yoga stretching for 90 min is associated with a significant enhancement in the parasympathetic nerve activity.”

You can read the study in full via the link. But here’s a summary :

“To our knowledge, this is the first to investigate changes in cardiac autonomic nervous system after yoga stretching. We confirmed that salivary cortisol concentration decreased and T/C ratio increased after yoga stretching. As the major finding of this study, yoga stretching for 90 min significantly enhanced parasympathetic nerve activity, and the beneficial effect was observed much later, at approximately 60 min after yoga stretching.

In men, salivary and blood testosterone concentrations have showed significant correlations (Sannikka et al., 1983; Vittek et al., 1985). Salivary testosterone is known to increase in response to acute high-intensity exercise (Budde et al., 2010a; 2010b), but it remains unchanged after acute low- or moderate-intensity exercise (Budde et al., 2010b). However, in the present study, the testosterone level tended to increase at 120 min after yoga, and this increase in testosterone level was confirmed in a previous study (Eda et al., 2018). Testosterone contributes to an increase in protein synthesis and a decrease in protein degradation and thus enhances muscle growth and strength-related performance (Crewther et al., 2006; Papacosta and Nassis, 2011). On the other hand, testosterone levels are known to decrease with age, and previous studies have reported that lower testosterone levels are associated with a higher risk of metabolic syndrome, cardiovascular disease, type 2 diabetes, and mortality (Haring et al., 2010; Jones, 2010). The increase in the testosterone level in the present study indicates that yoga stretching may promote muscle growth and strength-related performance in athletes and decrease the risks of lifestyle-related diseases and mortality in the general population.

Cortisol is a member of the glucocorticoid family and is secreted from the adrenal cortex via the hypothalamic–pituitary–adrenal axis (Papacosta and Nassis, 2011). The level of cortisol is known to increase in response to mental and physical stress and decrease in response to relaxation. Cortisol concentrations in the blood and saliva have showed significant correlations (Cadore et al., 2008; O’Connor and Corrigan, 1987). In a previous study, African dance for 90 min increased and yoga for 90 min decreased salivary cortisol concentration significantly (West et al., 2004). A previous study also showed that salivary cortisol concentration decreased after yoga stretching (Eda et al., 2018). In the present study, the cortisol level decreased at 120 min compared with that at pre in the YOG trial. This finding is consistent with those in previous studies, and the significant decrease in cortisol after yoga in the present study may demonstrate the relaxing effect of yoga stretching.

In this study, cardiac vagal activity was assessed by measuring HRV.

Improvements in stress hormones, autonomic nerve activity, and mood states are effective in preventing depressive psychosis and lifestyle-related diseases. In this study, these parameters improved after yoga; therefore, we suggested that yoga may be useful to compensate for physical inactivity and increase life expectancy in the general population.”