THE EFFECTS OF PRACTICE ON MOVEMENT DISTANCE AND FINAL POSITION REPRODUCTION - IMPLICATIONS FOR THE EQUILIBRIUM-POINT CONTROL OF MOVEMENTS

Predictions of two views on single-joint motor control, namely program ming of muscle force patterns and equilibrium-point control, were comp ared with the results of experiments with reproduction of movement dis tance and final location during fast unidirectional elbow flexions. Tw o groups of subjects were tested. The first group practiced movements over a fixed distance (36 degrees), starting from seven different init ial positions (distance group, DG). The second group practiced movemen ts from the same seven initial positions to a fixed final location (lo cation group, LG). Later, all the subjects were tested at the practice d task with their eyes closed, and then, unexpectedly for the subjects , they were tested at the other, unpracticed task. In both groups, the task to reproduce final position had lower indices of final position variability than the task to reproduce movement distance. Analysis of the linear regression lines between initial position and final positio n (or movement distance) also demonstrated a better (more accurate) pe rformance during final position reproduction than during distance repr oduction. The data are in a good correspondence with the predictions o f the equilibrium-point hypothesis, but not with the predictions of th e force-pattern control approach.