Changes in movement final position associated with agonist and antagonist muscle fatigue

We have tested the hypothesis that agonist and antagonist muscle fatigue co uld affect the final position of rapid, discrete movements. Six subjects pe rformed consecutive elbow flexion and extension movements between two targe ts, with their eyes closed prior to, and after fatiguing the elbow extensor muscles. The results demonstrate that elbow extension movements performed in the post-test period systematically undershot the final position as comp ared to pre-test movements. However, attainment of the aimed final position in elbow flexion movements was unaffected by fatiguing of the extensor mus cles. Undershoot of the final position obtained in extension movements was associated with agonist muscle fatigue, a result that was expected from the point of view of current motor control theories, and that could be explain ed by a reduced ability of the shortening muscle to exert force. On the oth er hand, the absence of the expected overshoot of the final position when t he antagonist is fatigued, indicates the involvement of various reflex and/ or central mechanisms operating around the stretched muscle that could cont ribute to returning the limb to the standard final position after a brief p rominent overshoot.