Coordination of Kinematic Events during Simple Arm Movements

Abstract

This paper examines the pattern of kinematic events underlying repeated performance of simple rapid elbow flexion movements to a fixed target. The limb positions and time samples of kinematic indices are derived from forearm movement trajectories and measurements of the forces tangent to the arch described by the forearm during motion. The pattern of kinematic events are compared for different levels of the inertial load moved, distance traveled and target width. Results demonstrate that both time samples and limb positions corresponding to peak acceleration, peak velocity and peak deceleration varied significantly with inertial load and movement distance, but were relatively unaffected by changes in target width. Changes in the timing of kinematic events demonstrated no clear pattern across manipulations. Forearm positions, however, were highly proportional to the movement distance, with peak acceleration approximately 7% of the distance to the target, and peak velocity and deceleration approximately 47% and 87% of the distance to the target, respectively. These results are interpreted as indicating that the control processes governing the construction of motor commands are organized in terms of limb position instead of more traditional force-time representations. Mechanisms of this type are consistent with recent mass-spring models of muscle control.