The Repeat Bout Effect Following Initial Low and High Volume Eccentric Exercise

Abstract

2195 An initial bout of eccentrically biased exercise protects skeletal muscle against damage in subsequent bouts, but the volume required to elicit protection is unclear. One mechanism that could mediate this protective effect is a shift in motor unit recruitment in the repeat bout, towards motor units that were used to a lesser extent or not at all in the initial bout. PURPOSE: To compare markers of muscle damage and surface electromyography (EMG) activity from an initial low volume (LV) or high volume (HV) bout followed by a subsequent HV bout of maximal eccentric exercise. METHODS: Sixteen males were assigned to a LV or HV group (10 and 45 maximal eccentric contractions of the elbow flexors, respectively). Surface EMG activity was recorded during the first 10 contractions of each bout from the biceps brachii. The damage markers of creatine kinase (CK), soreness rating (DOMS) and maximum isometric strength (MVC) were measured before, 48 h and 96 h after the initial exercise and at the same time periods before and following a subsequent bout of HV eccentric exercise performed 14 days later. RESULTS: DOMS (F = 19.3) and MVC (F = 11.7) showed significant (p<0.01) group × bout interactions; both DOMS (69.5%) and MVC (13.2%) were attenuated (p<0.01) in bout 2 for the HV group, however there were no differences between groups in bout 2. Median frequency (MDF) significantly decreased from the initial bout to the subsequent bout by 9.7% (F = 9.4, p<0.01), without differences between groups. Eccentric torque in the first 10 contractions increased non-significantly between bouts (8.8%). CONCLUSIONS: Both LV and HV maximal eccentric exercise produce a repeat bout effect in subsequent HV bouts. It would appear that any changes eliciting a repeat bout effect may be attributed, at least in part, to a neural adaptation in the first 10 maximal eccentric contractions of the initial exercise bout. The reduction in MDF may indicate a shift in motor unit recruitment that is independent of the volume of the initial exercise bout.