Passive visco-elastic properties of the structures spanning the human elbow joint.

Abstract

The passive elastic torque function and the passive viscous torque function of the muscles and connective tissues spanning the elbow joint have been determined in three adult male subjects. The procedure for estimating the passive elastic torque involved measurement of the torque required to passively move the forearm-hand segment, at a constant angular velocity, throughout a complete range of elbow joint motion. The “suspension method” (Hatze, 1975) was used to obtain the estimate of passive viscous torque. Both of these torque functions were shown to be nonlinear functions of the angular displacement of the joint. In order to assess whether myotatic reflex activity was contributing to the damping of the segment, and thereby biasing the value of the torque contributed by passive viscous elements, the surface electromyograms of the biceps brachii and brachioradialis muscles were examined while the suspended body segment was oscillated. In one subject there was firm evidence of involuntary muscle activity in the brachioradialis muscle which tended to distort the oscillogram. This activity was enhanced when the subject maintained a voluntary isometric contraction in a remote muscle group (Jendrassik's manoeuvre). Based upon these observations, recommendations have been made for reducing unwanted myotatic reflex activity while using the “suspension method” to obtain estimates of various biomechanical parameters.