Sensory effects of pulling or vibrating exposed tendons in man

The role of muscle receptors in proprioception has been demonstrated in a variety of ways (for review see McCloskey, 1978) but is still doubted by some. One simple but critical experiment has produced conflicting results: when a tendon of a conscious subject is exposed at operation under local anaesthesia, and pulled so as to stretch its muscle while the joint at which the muscle acts is held still, the subject is claimed by some to perceive nothing (Gelfan and Carter, 1967; Moberg, 1972), while others claim that the subject feels that the joint seems to move (Matthews and Simmonds, 1974). In the present study 4 patients were studied while undergoing surgery at the wrist or hand under local anaesthesia, and a more extensive study was carried out in the laboratory on the exposed, transected tendon of extensor hallucis longus of one of the authors (D.I.McC.). All 4 patients and the experimental subject detected stretches imposed on their muscles, and reported them as rotations of the joint or joints to which those muscles attach. In all cases the movements reported were in the direction of joint rotation that would normally stretch the muscle tested. In the experimental subject it was shown that stretches were detected with comparable acuity to that demonstrable for the detection of movements imposed on the intact toe. Also, the subject was able to detect, as joint movements, sinusoidal stretches of less than 1 mm imposed on the tendon at 1 or 5 Hz. The experimental subject experienced illusory movements of plantar flexion of the big toe when longitudinal vibration at 100 Hz, 20 to 100 microns amplitude was applied. These were sometimes partly masked by spread of the vibration through the foot. These vibration-induced illusions correspond to those reported by Goodwin et al. (1972) for transverse vibration applied through the skin. The subject could maintain a constant tension through the tendon in a contraction in which his effort was held constant. If, during such an effort, a downward movement was imposed on the toe to which the tendon normally connects, or the skin on the bottom of the toe was scratched, achieved tension fell.