Control of Postural Reactions in Man: The Initiation of Gait

This study seeks to establish how locomotion is initiated and to characterize the role of central and/or peripheral mechanisms in the control of this behaviour. Initiation of gait is defined as a series of postural reactions in both the swing and stance limbs. Postural reactions of both lower limbs were assessed after an auditory signal (AS) on a “walkway” (by recording myoelectric potentials from the TA, MG, S, RF, VM, MH, BiF, G.Med., G. Max. muscles (the abbreviations are defined in the Methods); joint position of ankle, knee and hip; amplitude and position of vertical forces; and moments (torque) about the ankle joints) through one complete stride of the swing leg and through toe-off of the stance leg. The influence of muscle and joint afferents was evaluated by differential suppression of the tibial nerve with dilute solutions of Xylocaine, by inhibiting the excitation-coupling reaction of muscle with a peroral administration of dantrolene sodium, and by restraining joint motion with a below-knee orthosis. In both limbs, the gait was initiated, before angular displacement, by a sudden reduction in EMG activity of the MG and S muscles (e.g. 150 msec after AS) followed shortly by an intense discharge in the TA muscle and to a lesser degree in the RF and G.Med, muscles.

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