Neuromuscular activation and the load sharing concept

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Massey, Keith James
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Purpose. The complex interaction between the multiple neural, mechanical and intrinsic muscular factors responsible for muscle damage during voluntary movements has not been well elucidated. Specifically, the association between neural recruitment strategies used to activate muscles during voluntary exercise and the occurrence of muscle damage has not been examined. The purpose of this study was to explore the role of motor unit activation strategies in the initiation of exercise induced muscle damage. In addition, this study was undertaken to examine electromyographic signals (EMG) from the knee extensor muscles during concentric, eccentric and isometric contraction in order to examine possible differences in neural activation strategies between contraction types and contraction velocities. Methods. Isovelocity knee extensor strength tests were performed before and 24 hours after low level electrically evoked eccentric exercise of the quadriceps muscle (n = 6). Surface EMG was measured from the knee extensor muscle during maximum voluntary isovelocity knee extensor strength tests (3 repetitions, $\pm$50, 100, 150, 200, 250$\sp\circ$/s) for 8 subjects. Neuromuscular model. Isometric force and muscle fiber loading resulting from different neural activation strategies was simulated using a model based on human motor unit twitch properties. (Abstract shortened by UMI.)