Neuromuscular fatigue during a prolonged intermittent exercise: Application to tennis

The time course of alteration in neuromuscular function of the knee extensor muscles was characterized during a prolonged intermittent exercise. Maximal voluntary contraction (MVC) and surface EMG activity of both vastii were measured during brief interruptions before (TO), during (30, 60, 90, 120, 150 and 180 min: T-30, T-60, T-90, T-120, T-150, T-180) and 30 min after (T+30) a 3 h tennis match in 12 trained players. M-wave and twitch contractile properties were analyzed following single stimuli. Short tetani at 20 Hz and 80 Hz were also applied to six subjects at T-0 and T-180. Significant reductions in MVC (P < 0.05; -9%) and electromyographic activity normalized to the M wave for both vastii (P < 0.01) occurred with fatigue at T-180. No significant changes in M-wave duration and amplitude nor ill twitch contractile properties were observed. The ratio between the torques evoked by 20 Hz and 80 Hz stimulation declined significantly (P < 0.001; -12%) after exercise. Central activation failure and alterations in excitation-contraction coupling are probable mechanisms contributing to the moderate impairment of the neuromuscular function during prolonged tennis playing. (C) 2007 Elsevier Ltd. All rights reserved.