This study investigated the hypothesis that the protective effect conferred by a low-intensity eccentric exercise against maximal eccentric exercise would not last more than a week. Untrained men (21.3 ± 1.6 years) were allocated into either a control or one of four repeated bout groups (n = 13 per group). The repeated bout groups performed 30 low-intensity eccentric contractions (ECC) of the elbow flexors with a dumbbell set at 10% of maximal isometric strength (10%-ECC) either 2 days, 7 days (1 week), 14 days (2 weeks) or 21 days (3 weeks) before 30 maximal eccentric contractions (Max-ECC). The control group performed Max-ECC only. Changes in maximal voluntary contraction strength, optimum angle, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration, and ultrasound echo-intensity following 10%-ECC were analysed by a one-way repeated measures ANOVA. Changes in the variables following Max-ECC were compared among the groups by a two-way repeated measures ANOVA. The 10%-ECC did not change any variables, showing no indication of muscle damage. The changes in all variables following Max-ECC were smaller (P < 0.05) for 2-day, 1- and 2-week groups than control group, without significant differences between 2-day and 1-week groups. The 2-week group showed greater (P < 0.05) changes in all variables compared with 2-day and 1-week groups. Changes in the variables were similar between 3-week and control groups, except for muscle soreness showing smaller (P < 0.05) changes for 3-week group. These results suggest that non-damaging eccentric exercise confers a protective effect against Max-Ecc, but the effect is attenuated between 1 and 2 weeks.
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