Jo, E., Zourdos, M. C., Wilson, J. M., Nosaka, K. K., Lee, S.-R., Naimo, M., Henning, P. C., Park, Y.-M., Khamoui, A. V., Park, B.-S., Panton, L. B., & Kim, J.-S. (2012). Varying muscle-specific exercise between consecutive training sessions does not diminish the repeated bout effect. Presentation 1876 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

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"Repeated high-intensity contractions produce significant myofiber damage leading to a period of decreased force production, soreness, and edema. However, the repeated bout effect indicates that if the same exercise is repeated within six months, the magnitude of muscle damage is attenuated compared to that ensuing the initial exercise bout. Myofiber damage has been previously considered a key stimulus for muscle hypertrophy. However, it has been recently shown that muscle growth may manifest independent of myofiber damage. Thus, invoking the repeated bout effect may be advantageous to minimize undue fatigue during muscle hypertrophy training. However, it remains undetermined if varying muscle-specific exercise selection between consecutive training bouts diminishes the repeated bout effect."

This study determined if muscle-specific exercise variation between successive training sessions alters the magnitude of the repeated bout effect in healthy, untrained males (N = 20). Ss were assigned to one of two groups: 1) two sessions of dumbbell incline curls (N = 10), or 2) one session of dumbbell incline curls and one session of dumbbell preacher curls (N = 10). The two training sessions for each group were separated by seven days. Both groups performed 5 sets of 6 repetitions of each exercise at ~50% of maximal isometric elbow flexor strength in both training sessions. Muscle damage indices included range of motion, muscle soreness, maximal voluntary isometric contraction, and serum creatine kinase and lactate dehydrogenase, were measured at pre-, and immediate post-exercise, 24, 48, 72, and 96 hours after each training session.

Following the first session, range of motion decreased and muscle soreness increased significantly up to 72 hours, while maximal voluntary isometric contraction significantly declined by 15% immediately after the exercise. Serum creatine kinase was significantly elevated by 28% 48 hours post-exercise while lactate dehydrogenase increased immediately after the exercise. There were no significant differences in these responses between groups. After the second session, both groups demonstrated similar damage responses of the repeated bout effect with maximal voluntary isometric contraction declining only 7.5% immediately after the exercise.

Implication. Variation of muscle-specific exercise between consecutive training sessions does not alter the magnitude of the repeated bout effect.

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