Effects of Force Output and Preparatory Set on Premotor Time of Simultaneous Bilateral Responses

Premotor times in simultaneous bilateral elbow-flexion movements were measured for 20 subjects when loads (light or heavy) were applied to both elbow joints. Premotor times for the heavy load were longer than those for the light load on both sides. The difference in premotor time between the two loads was larger for bilateral response than for unilateral response, suggesting that exertion of strength combines with response modality to increase the difference between the two loads. Preparatory set did not affect premotor time under the heavy load but affected premotor time under the light load. Possible mechanisms subserving these findings are discussed.