The repeated bout effect of reduced-load eccentric exercise on elbow flexor muscle damage

In this study we investigated the extent to which an initial eccentric exercise consisting of two (2ECC) or six maximal eccentric actions (6ECC) of the elbow flexors would produce a similar effect to 24 maximal eccentric actions (24ECC), on a second bout of 24ECC performed 2 weeks later. Male students (n = 34) were assigned to one of three groups, and with their nondominant arm performed either 2ECC (n = 12), 6ECC (n 10), or 24ECC (n = 12) as a first bout of exercise. Two weeks later all groups performed 24ECC. Maximal isometric strength, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration were assessed before, immediately after, and for 4 days after exercise. Changes in all variables were compared between the bouts and groups by a two-way repeated measures analysis of variance. All variables changed significantly (P < 0.05) after 2ECC, 6ECC, and 24ECC, but the amount of change after 2ECC and 6ECC was significantly smaller (P < 0.05) than both 6ECC and 24ECC, and 24ECC, respectively. After the second bout, the 6ECC and 24ECC groups showed a profound repeated bout effect, and no significant differences were found between the groups. All variables except muscle soreness were significantly (P<0.05) larger after the second bout for the 2ECC group, however the changes observed after 24ECC were significantly smaller (P<0.01) than those observed after the first 24ECC of the 24ECC group. These results suggest that it is not necessary to conduct a high number of eccentric actions in the first bout to elicit a repeated bout effect in a subsequent bout performed some time later.