NONLINEAR CONTROL OF MOVEMENT DISTANCE AT THE HUMAN ELBOW

The kinematic, kinetic, and electromyographic (EMG) patterns observed during fast, single-joint flex ion movement have been widely studied a s a paradigm for understanding voluntary movement. Several patterns ha ve been described that depend upon the movement task (e.g., distance, speed, and load). A previous model that interpreted differences in EMG patterns in terms of pulse-height or pulse-width modulation of rectan gular pulses of motoneuron pool excitation cannot explain all the EMG patterns reported in the literature. We proposed a more general versio n of that model, consisting of a set of four equations, which specify the parameters of the excitation pulses for a wide variety of movement tasks. Here we report experiments in which subjects performed fast el bow flexions over a range of distances from 2.8 degrees to 45 degrees. The EMG patterns that we observe are consistent with this more genera l model. We conclude that this model is sufficient to specify muscle e xcitation patterns that will launch a movement toward and stop it in t he neighborhood of a target. This model operates on the basis of prior knowledge about the task rather than feedback received during the tas k.