Muscle activities during pushing movement with risk of forward disturbance

Abstract

In competitive sports such as judo and sumo, in which opponents wrestle with each other, evasive actions by one opponent who has predicted the move of the other can lead to the toppling of a lager opponent. This study examined muscle activities associated with known and unknown perturbation induced by a forward bilateral pushing movement. Participants stood upright and voluntarily pushed a lever at a maximal strength in two tasks: one where the lever was free to be moved by the participant (perturbation; movable task) or the other where it was blocked by the experimenters (stationary task). The degree of predictability of the lever’s mobility was manipulated by the experimenters. Displacement of body segments, electromyography and pushing strength observed during each task were recorded, and the following main results were obtained. Under condition that the participant did not know the movement of the lever in advance, preliminary activity for perturbation was observed with a start of the pushing movement. However, after the timing of perturbation onset, the muscle activity corresponding to each task was found to be within 100 ms. Given these results, it is suggested that the movement is initiated based on the motor commend that corresponding to perturbation under conditions of uncertain prediction, and after the movement is started, it is then modified with a short latency in accordance with the motor command that corresponds to the movement of the lever.