The purpose of the present study is to examine the effects of indoor exercise to circadian pacemaker in humans. In the first study, 24 young healthy subjects were equally divided into 3 groups. They spent 15 days alone in a temporal isolation room where the light intensity was less than 50 lx during the waking period. Sleep-wake cycle and rectal temperature was continuously recorded and plasma melatonin was measured on days 1, 8 and 14. In the first group, subjects had no instructions to sleep and wake (F group). In the second, subjects were directed to sleep and were awakened from outside through interphone to follow 23.67-hr forced sleep-wake schedule (FS group). In the third, subjects followed the 23.67-hr forced sleep-wake schedule and did 2-hr exercise at 2 and 7 hr after wake-up during every waking period (FSE group). The free-run period of plasma melatonin rhythm was 24.37 hr in F group, 24.06 hr in FS group, and 23.88 hr in FSE group. The free-run periods in FS and FSE groups were significantly shorter than in F group, and the melatonin rhythm in FSE group was significantly shorter than in FS group and almost entrained to the forced sleep-wake schedule. In the second study, 24 subjects were equally divided into 3 groups and spent 3 days alone in the isolation room. Each group did 2-hr exercise in the morning (9:00-11:00), afternoon (15:00-17:00), or night (0:00-2:00). The plasma melatonin rhythm was significantly phase-delayed in the afternoon and night exercise groups but was not changed in the morning exercise group. The present study demonstrated that non-photic zeitgeber such as forced sleep-wake schedule and repeated indoor exercise phase-shifts circadian pacemaker but single morning exercise did not in humans. These results indicate that habitual indoor exercise controls the circadian pacemaker and is beneficial for stabilizing circadian rhythms.

DESCENTE SPORTS SCIENCE Vol.21/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE