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 are described here, using human subjects, in which the effects of eccentric and concentric exercise of elbow flexor muscles are compared on the sense of forearm position and the sense of tension in elbow flexors. Subjects were required to compress a preloaded spring with one arm, carrying out a concentric contraction in elbow flexors, then flexors of the other arm released the spring from compression and thereby carried out an eccentric contraction. The force of the spring was adjusted to be 20% maximum voluntary contraction (MVC), and each subject carried out a minimum of 120 contractions. Position sense was measured in blindfolded subjects by placing one forearm at a set angle and asking subjects to match it by positioning the other arm. Over 4 days postexercise, subjects placed the eccentrically exercised arms in a more extended position than the concentrically exercised arm suggesting that they thought the muscle was shorter than it actually was. In a force-matching task, subjects systematically undershot the target 10% MVC with their eccentrically exercised arm. Since it is known that eccentric exercise is associated with damage to muscle fibres, it is postulated that this leads to a disturbance of muscle receptors, the muscle spindles and tendon organs.