Influence of 'strategy' on muscle activity during ballistic movements.

Human subjects were asked to grasp the handle of a manipulandum and to track a visual target with ballistic flexion or extension movements of the wrist. Prior to each trial subjects were given verbal instructions in order to influence their movement strategy. A burst of EMG activity was recorded from extensor carpi radialis (ECR) when subjects intended to terminate ballistic flexion movements within the target (antagonist burst). The antagonist burst in ECR was reduced or abolished during ballistic flexion movements when subjects intended to bang the manipulandum handle against a mechanical stop. Thus, our major observation is that antagonist muscle activity during ballistic movements is controlled by a subject's movement strategy.