Systematic positioning errors in human voluntary single-joint movements without visual guidance

Abstract

Healthy subjects underwent analysis for positioning accuracy. The flexion-extension movements in the ankle and elbow joints performed without visual control were studied. The movements were produced by flexor muscles against small background loading (extensors were inactive). The subject was asked to memorize a certain target value of the joint angle reached under visual guidance in the phase of flexor contraction. After the flexion- (additional activation of the flexors) or extension-directed movement (relaxation of these muscles) the subject was asked to restore the target level “from memory,” without visual guidance. In the first case, when the target level was finally approached due to the flexor relaxation, a systematic overshoot of the target joint angle was observed. In the second case, when the target level was finally approached due to the additional activation of the flexors after their temporal relaxation, the positioning was much more accurate.