Sequential processes for controlling distance in multijoint movements.

The purpose of this study was to examine the mechanisms underlying control of distance during multijoint movements in different directions. The findings revealed 2 sequential muscle torque impulses, which correlated with 2 events in the hand acceleration profile. These 2 events occurred prior to peak velocity, characterizing control in the initial acceleration phase of motion. The contribution of shoulder and elbow joint torque to each event varied with movement direction. However, regardless of direction, these 2 torque events appeared to be functionally distinguishable: a preplanned initiation event was responsible for the initial hand acceleration, whereas a 2nd modulation event adjusted acceleration in compensation for variations in acceleration. Thus, the findings support the idea that control of distance during multijoint movement occurs through sequential control mechanisms.