6533b85dfe1ef96bd12be4c0

RESEARCH PRODUCT

Dépendance de la fatigue à la longueur musculaire : approche mécanique et neurophysiologique

subject

description

The objective of this work is to evaluate the fatigue dependency on the knee extensor muscles length. Exercises varying the type of contraction (isometric and eccentric) and intensity of contraction (maximal and sub-maximal) are performed in order to disrupt the neuromuscular system by different factors of fatigue: central and peripheral. These exercises are performed at two muscular lengths (S and L, corresponding respectively to 40 and 100° of knee flexion). Neuromuscular parameters (maximal torque, muscular twitch, voluntary activation level, electromyographic activity, etc.) are analyzed in pre- and post-fatigue conditions in the type of contraction required by the fatiguing exercise. In order to compare these parameters for the same level of fatigue between S and L, exercises are maintained until an identical reduction of the voluntary torque is obtained. The results demonstrate, under non-fatigue conditions, an activation level dependency (twitch interpolation technique) on muscle length during isometric and eccentric maximal contractions. Activation is higher for long muscle lengths contraction. This phenomenon is maintained with fatigue. Moreover, it is observed that, whatever the type and intensity of the contraction, fatigue appears more rapidly at long than at short muscular lengths. The mechanical strain induced at the level of the sarcomeres by the contraction of the muscle mobilized in a stretched position would cause, during the fatiguing exercises, a stress of the muscular structure which could even reach to damages. This effect would explain the more rapid decrease in strength at long muscle lengths. When fatigue is induced from submaximal contractions, different adaptations between mono- and bi-articular muscles appear. Activation of the knee extensor muscles would depend on their ability to produce force at the mobilized muscular length. These results can be applied in the prevention of work-related musculoskeletal disorders.