The effects of muscle vibration on the attainment of intended final position during voluntary human arm movements

Muscle tendon vibration was applied during voluntary step-tracking arm target-movements performed by normal human subjects. Vibration (freq. = 120 Hz) was applied over either the biceps or triceps tendons. During non-visually guided (eyes closed) trials, vibration of the muscle antagonistic to the movement being performed resulted in an undershoot of the required target. Thus, biceps vibration produced an undershoot of the extension target and triceps vibration an undershoot of the flexion target. The same effect occurred if the vibration was applied continuously over several movements or only during the course of individual movements. In contrast, vibration of the muscle acting as the prime mover had no effect on the correct attainment of the required target. It is suggested that the central nervous system may monitor muscle afferent activity of the lengthening (antagonist) muscle during simple, step movements.