The repeated bout effect on changes in muscle damage indicators was examined in two groups of subjects following two bouts of 70 maximal eccentric actions of the forearm flexors. Fourteen college age female subjects were placed into two groups. The two bouts were separated by 6 weeks (n=6), and 10 weeks (n = 8). The subjects performed the same amount of work for the bouts. The muscle damage indicators were isometric strength (STR), relaxed elbow joint angle (RANG), flexed elbow joint angle (FANG), perceived muscle soreness ratings (SOR), and plasma creatine kinase activity (CK). These measures were obtained pre-exercise and 5 days following each bout. The first bout showed significant changes in all measures over time for both groups (P<0.01). For the 6-week group, significantly smaller changes in RANG (P < 0.01), SOR (P<0.05), and CK (P<0.01), as well as significantly faster recoveries (P<0.05) for STR and FANG were produced in the second bout. For the 10-week group, significantly smaller changes in RANG (P<0.05) and CK (P<0.01) were demonstrated by the second bout, but no significant difference was found for STR, FANG, and SOR between bouts 1 and 2. Changes in CK were still significantly smaller than that of the first bout when 6 subjects (3 subjects from each group) performed the same exercise 6 months after the second bout, but no difference in other measures. It is concluded that the length of the adaptation effect varies among the indicators of muscle damage and that the duration of the adaptation for CK is dramatic.