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CHANGES IN SURFACE ELECTROMYOGRAPHY AND RATE OF FORCE DEVELOPMENT FOLLOWING MAXIMAL ECCENTRIC AND CONCENTRIC EXERCISE

Abstract

BACKGROUND: The purpose of this study was to examine the time-course in recovery of rapid force characteristics following maximal eccentric (ECC) or concentric (CON) contractions. METHODS: Seventeen strength-trained college-aged males completed this randomized, cross-over study. Subjects completed 6 sets of 10 repetitions of maximal unilateral ECC or CON contractions of the elbow flexors on an isokinetic dynamometer at 60°/s with 2 min rest between sets. Peak rate of force development (pRFD) and peak rate of electromyography (EMG) rise (pRER) were assessed instantaneously during a 10 ms window during a maximal voluntary isometric contraction (MVIC) at 90° of elbow flexion before (PRE), immediately after (POST), 1-hour (POST1), 24- (POST24), 48- (POST48), and 72-hours (POST72) post-exercise. Separate 2 (condition) × 6 (time) repeated measures ANOVAs were run for each dependent variable. RESULTS: There was no significant interaction effect for pRFD (p=0.257), however, there were significant main effects for condition (p=0.001) and time (p<0.001). Post-hoc analysis revealed that when collapsed across time, pRFD was significantly lower in ECC (2681.7±725.1 N s-1) than CON (3063.1±673.6 N s-1; p=0.001). When collapsed across condition, pRFD was significantly greater at PRE (3754.0±1366.5 N⸱s-1) when compared to all other time points (p<0.001-0.002). pRFD was reduced at POST (2337.5±679.9 N s-1) and POST1 (2454.4±788.1 N s-1) when compared to POST24 (2866.9±887.9 N s-1; p=0.001-0.012), POST48 (2907.6±1128.7 N s-1; p=0.007-0.027), and POST72 (2914.0±1014.9 N s-1; p=0.003-0.005). There was a significant interaction effect for pRER (p=0.028) by which, during ECC, pRER decreased from PRE (1.06±0.61 mV/s) to POST (0.77±0.41 mV/s; p=0.051), remained depressed at POST1 (0.72±0.48 mV/s; p=0.004) before recovering to baseline at POST24 (1.11±0.61 mV/s; p=0.033), which did not differ from POST48 (1.03±0.63 mV/s; p=0.863) or POST72 (1.15±0.47 mV/s; p=0.645). pRER was significantly lower in ECC at POST and POST1 when compared to CON (POST: 0.98±0.41 mV/s; POST1: 1.09±0.63 mV/s; p=0.043-0.048). During CON, pRER was significantly greater at PRE (1.35±0.87 mV/s) when compared to POST72 (0.95±0.47 mV/s; p=0.035). CONCLUSIONS: The findings of the present study suggest that pRER may be more sensitive than pRFD at discriminating contraction-specific changes in neuromuscular function following an acute bout of exercise.

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