Effects of a Single Bout of Intensive Eccentric Contractions at Varying Repetitions on Muscle Damage

Abstract

This study examined whether performing different repetitions of a single bout of eccentric contractions would cause differing magnitudes of muscle damage and result in different recovery rates. A group of college-age male students (N=36) was recruited for the study. were randomly assigned into 24 (EC24; n=12), 50 (EC50 n=12), They and 70 (EC7O; n=12) eccentric exercise groups. A single bout of intensive eccentric exercise (EGG) was 24, 50, and 70 repetitions for EG24, EG50, and EG70, respectively, on nondominant elbow flexors using a dumbbell that was set at 80% of the pre-ECC MIF level. Upper arm circumference (CIR), ROM, MIF and plasma CK activity were measured before and immediately after ECC, and every 24 hours for 9 consecutive days after EGG for all groups. Muscle soreness was assessed before and for 9 consecutive days after ECC for all groups. There were significant changes (p＜.05) in all criterion measures following ECC for all groups. There were dramatic changes (p＜.05) in MIF ROM, GIR, and CK for EC70 as compared to EG50 and EG24 following ECC. Moreover there were no significant changes (p＞.05) after ECC among groups Furthermore, the recovery rate of MIF ROM, CIR, and CK for ECC for EC70 was slower after ECC among groups. Furthermore, the recovery rate of MIF ROM, CIR, and CK following ECC for EG70 was slower (p＜.05) than the EC50 and EC24 groups; and EG50 had a significantly slower (MIF, ROM, CIR, CK, p＜.05) recovery rate from muscle damage after ECC than EC24. The results of the present study showed that the larger the number of eccentric contractions, the greater the changes (p＜.05) in criterion measures (MIF, ROM, CIR, CK) and the slower the recovery rate (p＜.05) of muscle damage after ECC. Moreover there was a significant increase (p＜.05) in soreness following ECC for all groups. Therefore, this may provide a possible explanation for the different magnitude of muscle damage from ECC and the different recovery rate of muscle damage after ECC for each group. However muscle soreness following ECC showed no significant differences (p＞.05) among groups. Furthermore, use of muscle soreness may not a good indicator of exercise-induced muscle damage, and changes in indirect indicators of muscle damage are not necessarily accompanied with muscle soreness.