Effects of neuromuscular electrical stimulation on the contralateral repeated bout effect of the elbow flexor muscles

Abstract

PURPOSE: To examine the effects of neuromuscular electrical stimulation (NMES) on the contralateral repeated bout effect (CL-RBE) of the biceps brachii (BB). METHODS: Twenty untrained adults were randomly assigned into an ipsilateral (IL) or CL group, and completed 7 visits. Following a familiarization (visit 1), participants completed 3 maximal voluntary isometric contractions (MVICs) and submaximal trapezoidal contractions at 40% and 70% MVIC before and after 45 NMES to the BB muscle (1st bout) at pre (visit 2), post (visit 2), 1 day post (24post [visit 3]), and 2 days post (48post [visit 4]). The same procedures were performed for visits 5 (2nd bout), 6 (24post), and 7 (48post) on the same arm for IL or the contralateral arm for CL. Muscle damage markers (MVIC, elbow range of motion [ROM], visual analog scale [VAS] and pressure pain threshold [PPT] for muscle soreness and pain, and muscle thickness via ultrasonography were measured. Surface electromyography (EMG) and mechanomyography (MMG) were recorded from the BB. The EMG signals were decomposed to calculate y-intercepts and slopes for the motor unit (MU) mean firing rate (MFR) and MU action potential amplitude (MUAPAMP) vs. recruitment threshold (RT) relationships. The MMG amplitude (MMGRMS)-force relationships were log-transformed to calculate a and b terms for the linearly varying segments of the trapezoid. EMG amplitude (EMGRMS) and MMGRMS during steady force were normalized (N-EMGRMS, N-MMGRMS) to MVIC. Separate mixed factorial analysis of variance (ANOVAs) were performed. RESULTS: MVIC and ROM at post were less than pre, 24post, and 48post (p<0.05). Muscle thickness at pre was less than post (p<0.001) and 24post (p=0.019). PPT and the b terms at pre were greater (p<0.05) than post, 24post, and 48post. Y-intercepts for the MFR vs. RT relationships during the 70% MVIC were lower at post than pre (p=0.015), 24post (p=0.050), and 48post (p=0.016). VAS were lower (p=0.003) during the second bout (0.21±0.27cm) than the first bout (1.06±0.70cm) for the IL group. There were no significant differences between bouts for other dependent variables. CONCLUSION: Although there was an IL-RBE for VAS, the other variables did not support the existence of IL- or CL-RBE with NMES.