The purposes of the present study were to examine the relationship between exercise stress and heart rate variability. The subjects performed running exercise for 2 km with maximal effort, having the interval that was 24 hours, 1, 2 weeks, and 3 months. During and after exercise, beat to beat heart rate variability, gravitational change were monitored for 48 hours after exercise. Spectral analysis- of spontaneous heart rate fluctuation (1/fx) was calculated by MemCalc system, and total spectral power was divided into high frequency power (0.15-0.4 Hz : HF : parasympathetic nervous system activity indicator) and low frequency power (0.03-0.15 Hz : LF). During exercise, both LF and HF were depressed. In the case of 24 hours interval between exercises, the responses of heart rate fluctuation (1/fx) to exercise different from those in other exercise intervals.
　On the other hand, the responses of LF/HF (sympathetic nervous system activity indicator) to exercise after 1- week - interval were differed from those after exercise with other interval.However, the levels of heart rate and gravity during exercise, the time of running, and the responses of serum enzyme activities to exercise were almost constant all trials, independent on the interval of exercises. These results suggest that the spectral analysis of heart rate variability was a useful tool for the autonomic responses to exercise stress, the safety direction of exercise training, and the effective direction for training.

DESCENTE SPORTS SCIENCE Vol.17/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE