Eccentric Exercise-induced Muscle Damage And The Repeated Bout Effect Between The Elbow And Knee Flexors

It is well-documented that muscle damage induced by eccentric contractions is reduced when the same eccentric exercise is repeated within several weeks after the initial exercise bout. This adaptation is referred to as the repeated bout effect, and the effect is observed for not only the same muscle but also for the homologous muscle of the contralateral limb, which is known as the ipsilateral (IL-RBE) and contralateral repeated bout effect (CL-RBE), respectively. However, no previous study has investigated the magnitude of the CL-RBE to IL-RBE in the same interval, and whether this is different between the elbow flexors (EF) and the knee flexors (KF). PURPOSE: The current study compared the IL-RBE and CL-RBE of the EF and KF for the same interval between bouts. METHODS: A group of healthy sedentary young men (20-28 y) were placed into the IL-EF, IL-KF, CL-EF, and CL-KF groups (n = 13/group). The IL-EF and CL-EF groups performed 5 sets of 6 maximal isokinetic (30o/s) eccentric contractions of the EF, and IL-KF and CL-KF groups performed 6 sets of 10 maximal isokinetic eccentric contractions of the KF, with a 2-week interval between bouts. Changes in the maximal voluntary concentric contraction torque, range of motion, upper limb’s circumference, plasma creatine kinase activity, muscle soreness, position sense and joint reaction angle were measured before, immediately after, at 24 hours interval for 5 consecutive days after each bout. Changes in all dependent variables were compared between groups over time by a mixed-design of two-way ANOVA. RESULTS: Changes in all variables were greater (p < 0.05) after the first than second bout for all groups, and the changes were greater (p < 0.05) for the EF than KF. The changes in all variables after the second bout were greater (p < 0.05) for the CL than IL condition for the EF and KF, respectively. The index of protection of all variables was similar between CL-EF (33%) and CL-KF (32%), but slightly greater (p < 0.05) for IL-EF (67%) than IL-KF (61%). CONCLUSIONS: These results demonstrate that the magnitude of CL-RBE to IL-RBE was similar between the EF an KF (approximately 50%), although muscle damage was greater for the EF than KF for both bouts. Further studies investigating the mechanisms underpinning the CL-RBE and IL-RBE are warranted. Supported by National Science and Technology Council