Neuromuscular fatigue after resistance training

Abstract

This study examined the effects of heavy resistance training on dynamic exercise-induced fatigue task (5×10RM leg-press) after two loading protocols with the same relative intensity (%) (5×10RMRel) and the same absolute load (kg) (5×10RMAbs) as in pretraining in men (n=12). Maximal strength and muscle power, surface EMG changes [amplitude and spectral indices of muscle fatigue], and metabolic responses (i.e.blood lactate and ammonia concentrations) were measured before and after exercise. After training, when the relative intensity of the fatiguing dynamic protocol was kept the same, the magnitude of exercise-induced loss in maximal strength was greater than that observed before training. The peak power lost after 5×10RMRel (58–62%, pre-post training) was greater than the corresponding exercise-induced decline observed in isometric strength (12–17%). Similar neural adjustments, but higher accumulated fatigue and metabolic demand were observed after 5×10RMRel. This study therefore supports the notion that similar changes are observable in the EMG signal pre- and post-training at fatigue when exercising with the same relative load. However, after training the muscle is relatively able to work more and accumulate more metabolites before task failure. This result may indicate that rate of fatigue development (i.e. power and MVC) was faster and more profound after training despite using the same relative intensity.