The purpose of this study was to examine the quantitative limitation of endurance training from the view point of the effect of training.
　Thirty-two wistar strain male rats (49 days after birth) were classified into four groups, namely control group, 60 min. running group, 120 min. running group and exhaustive running group.
　After 8-week training period, histochemical and biochemical analyses were made on the gastrocnemius muscle.
　The results obtained were summarized as follows;
　1) In the running performance test at constant speed of 30 meter per min. 120 min. running group ran the longest time.
　2) The ratio of heart weight per body weight was higher with increase of training time, but the trend of hypertrophy in heart was leveling off in 120 min. running group.
　3) Capillary supply (number of capillaries per mm², per fiber, in contact with fiber and distance of diffusion) in training group was significantly higher than that of control group. It suggested the remarkable capillarization by training. But there was no difference in any parameters between 120 min. running group and exhaustive running group.
　4) Glycogen content was increase as training time increased, but the difference among four experimental groups were not significant.
　These results suggest that the exhaustive training is not necessary the optimal training for endurance training.

DESCENTE SPORTS SCIENCE Vol.5/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE