ABSTRACT
A study was conducted to examine the recovery of vagal activity after strenuous exercise based on changes in the magnitude of respiratory cardiac cycle variability, changes in the phase of this variability and the mechanism of the change. Six healthy male university students were studied for 5 h after exhaustive treadmill running. For cardiac cycle (RR) and blood pressure, the magnitude of respiratory variability and phase difference between respira-tory variability and respiration were measured. Respiratory period and tidal volume were maintained at 6 s and 21, respectively.<BR>1. The amplitude of respiratory RR variability decreased markedly after exercise and returned almost to normal after 2 h of recrvery. The phase of RR delayed with exercise, proceeded rapidly 2 h after exercise and progressively after that.<BR>2. The amplitude and phase of respiratory systolic blood pressure variability were almost stable before and after exercise.<BR>Based on these results, we conclude that vagal activity inhibited by strenuous exercise recovers about 2 h after the end of exercise. The delay in the phase of respiratory cardiac cycle variability with exercise may reflect inhibition of vagal activity.