Effects of consciously controlled slow breathing on cardiac parasympathetic nervous activity postexercise in young healthy males

The purpose of the present study was to clarify the effects of consciously controlled slow breathing on cardiac parasympathetic nervous activity Postexercise. Fifteen young healthy adult men participated in this study. They exercised on the bicycle ergometer at 50% of peak oxygen uptake for 10 min and then rested on the chair for 10 min. Two conditions were performed, namely slow breathing at 6 breaths per minute (SLOW) and spontaneous breathing (CON) at recovery phase in randomized order. We measured the oxygen uptake (V̇_O2), respiratory rate (RR), minute ventilation (V̇_E), tidal volume (V_T), ventilatory equivalents for carbon dioxide excretion (V̇_E/V̇_CO2), heart rate (HR), and R-R intervals. From the R-R intervals, we calculated the coefficient of variation of the R-R intervals (CVRR), the natural logarithms of the high-frequency (lnHF), and the natural logarithms of the sum of the components from very low- to high-frequency (total power: lnTP). There were no significant differences between conditions in V̇_O2 at exercise phase. At recovery phase in SLOW compared with CON, RR and V̇_E/V̇_CO2 were significantly decreased (both p < 0.001) with a slight decrease in V̇_E, and V_T was increased (p < 0.001). At recovery phase, while HR and lnHF had no differences between conditions, lnTP and CVRR were significantly higher in SLOW compared with CON (p < 0.05) and baseline phase (p < 0.05). In conclusion, slow breathing at six breaths per minute accelerated the reactivation of cardiac parasympathetic nervous activity Postexercise, accompanied by improved efficiency of pulmonary gas exchange due to a slight decrease in V̇_E.