Recently, there appeared increasing evidence that the biological clock can be manipulated using some factors other than light, i. e., ambient temperature, social cue, exercise, exogenous administration of melatonin and so on. These are of practical benefit for shift workers and travelers having rapid movement across time zones. With these in mind, we executed experiments to know whether the exercise by a bicycle ergometer could induce phase shift of human circadian rhythms including plasma melatonin and core temperature. Two male medical students served as subjects. Rectal temperature as core temperature was measured every 10 min using a thermistor probe and plasma melatonin was measured every hour using RIA method.
　The subject entered the bioclimatic chamber with kitchen, bed, living, shower and toilet at 5:00 p. m. on Friday and the measurements began at 6 : 00 p. m. and continued till 2 : 00 p. m. on Sunday for 44 hrs. Each subject experienced three series of experiment : control experiment, forenoon exercise experiment and afternoon exercise experiment. In control experiment no exercise was done, in forenoon exercise experiment exercise was done between 9 : 00 ~ 12 : 00 a. m. on Saturday (2nd day) and in afternoon exercise experiment exercise was done between 3 : 00 ~ 6 : 00 p.m. on Saturday (2nd day). Interval exercise of 15 min exercise and 15 min rest was carried out during these 3 hrs. Heart rates were also monitored during these 3 hrs.
　Main results can be summarized as follows :
　1) One out of two subjects showed about one hr advance of plasma melatonin rhythm and core temperature rhythm by afternoon exercise, while the other did not react to exercise. Increased level of plasma melatonin during afternoon exercise in subject A having showed the phase advance might be highly relevant to the phase adavance of melatonin rhythm and core temperature rhythm. The subject B having not shown the shift by the exercise did not increase plasma melatonin level during exercise, which might be responsible for no phase shift of rhythm in subject B.
　2) Rectal temperatures fell significantly lower after the end of exercise than those just before the beginning of exercise, and these lowered levels continued for 2-3 hrs.
　3) Heart rates during 15 min rest were clearly higher in the forenoon exercise. This means that the sympathetic tone is apt to continue after the forenoon exercise more strongly than after the afternoon exercise. Although much more experimentations are needful before definite conclusions should be drawn, it was suggested from present experiments that exercise could be properly used as tools to reset human circadian pacemakers to new light-dark cycles more rapidly.

DESCENTE SPORTS SCIENCE Vol.14/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE