A COMPARISON OF THE EFFECTS OF CONCENTRIC VERSUS ECCENTRIC EXERCISE ON FORCE AND POSITION SENSE AT THE HUMAN ELBOW JOINT

It is generally accepted that our sense of limb position and movement is provided, in part, by signals from muscle spindles, while the sense of muscle force derives from signals in tendon organs. Experiments ar e described here, using human subjects, in which the effects of eccent ric and concentric exercise of elbow flexor muscles are compared on th e sense of forearm position and the sense of tension in elbow flexors. Subjects were required to compress a preloaded spring with one arm, c arrying out a concentric contraction in elbow flexors, then flexors of the other arm released the spring from compression and thereby carrie d out an eccentric contraction. The force of the spring was adjusted t o be 20% maximum voluntary contraction (MVC), and each subject carried out a minimum of 120 contractions. Position sense was measured in bli ndfolded subjects by placing one forearm at a set angle and asking sub jects to match it by positioning the other arm. Over 4 days postexerci se, subjects placed the eccentrically exercised arms in a more extende d position than the concentrically exercised arm suggesting that they thought the muscle was shorter than it actually was. In a force-matchi ng task, subjects systematically undershot the target 10% MVC with the ir eccentrically exercised arm. Since it is known that eccentric exerc ise is associated with damage to muscle fibres, it is postulated that this leads to a disturbance of muscle receptors, the muscle spindles a nd tendon organs. (C) 1997 Elsevier Science B.V.