Les mécanismes neurophysiologiques du mouvement, base pour la compréhension du geste

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RESUME Comprendre les gestes de travail adoptés par l’opérateur constitue un enjeu essentiel en ergonomie. Le geste a pour fondement le mouvement volontaire. Cet article vise à préciser les notions de geste et de mouvement volontaire puis à présenter, à travers un ensemble d’approches expérimentales, les connaissances scientifiques les plus récentes dans le domaine de la neurophysiologie et de la biomécanique nécessaire à la réalisation du mouvement volontaire. Le mouvement volontaire résulte de l’interaction entre les segments corporels intentionnellement mobilisés, constituant la chaîne focale, et le reste des segments corporels, appelé chaîne posturale. La dynamique développée par la chaîne focale dépend étroitement de celle issue de la chaîne posturale laquelle est fonction de la posture initiale adoptée par le sujet et des surfaces sur lesquelles le sujet prend appui.

NEUROPHYSIOLOGIC MECHANISMS OF VOLUNTARY MOVEMENT : A BASIS FOR UNDERSTANDING GESTURE Understanding the gestures used by operators at work is a major issue in the field of ergonomics. Voluntary movement forms the basis of gesture. Knowing the processes required to execute a voluntary movement is essential if we are to understand the gestures adopted by operators. This paper aims to explain both gesture and voluntary movement. It then presents the most recent scientific knowledge in the field of neurophysiology and, through a series of experiments, the biomechanics necessary to perform voluntary movement. A voluntary movement results from an interaction between body segments which are intentionally mobilized, constituting the focal chain, and the remaining body segments, called the postural chain. Voluntary movement obeys the laws of physics and physiology. Its execution induces an endogeneous disturbance of body balance. In order to maintain balance, a counter-perturbation must be produced, which results from dynamics developed from muscular activities of the postural chain. These dynamics precede and accompany the voluntary movement. They are modified according to the initial posture adopted by the subject, the contact area between the subject and his supports, and the location and slipperiness of the support surfaces. The dynamics of the focal chain are closely dependent on those dynamics developed in the postural chain. Thus, the basis of a gesture is the outcome of organisational control over the way each muscle is brought into play and the coordination between the activity of different muscles to maintain a posture which is compatible with body balance and the requirements of the task.