The relationship between serum creatine phosphokinase (CPK) activity and labor strength was examined. Our epidemiological study showed thar the serum CPK activity in a group of men who worked over ten hours was significantly higher than that in the other groups who worked less than ten hours. In women, the serum CPK activity in a group who worked over seven hours was significantly higher than that in the other groups. The serum CPK activity in fishermen was significantly higher than that in

more »

... e engaged in other than fishery. In a laboratory study, test subjects were divided into 3 groups to perform 3 types (30%, 50%, 70% of VO2max) of exercise for 6 weeks. A rise in the serum CPK activity was noted in every group during exercise. The mean increase for these groups were 44.0 %, 48.1 % and 67.9 %, respectively.