Mechanically, the forearm is a one-jointed muscle-limb system that can be described as a rotational pendulum with inertia. The pendulum is subject to gravitation and driven by antagonistic muscles adding springlike elasticity and viscous damping. Surface EMG signals are considered to be monotonically or even linearily related to the number of muscle fibers recruited and their associated firing frequency. If this assumption is valid, EMG time series of the involved muscles should necessarily correlate with the time varying values of stiffness, damping, and equilibrium position. High correlations should be expected between (1) joint stiffness (K) and the summed EMG-activity of all muscles involved, (2) equilibrium position (x0) and the difference of antagonistic EMG activity, divided by their sum, and (3) the damping coefficient (B) and the EMG-activity multiplied by the difference between the angle of maximum stretch and actual position.
We recorded the kinematics, that are angular position, velocity and acceleration, of flexion/extension movements of the forearm during a center-hold task in 16 subjects. Based on the kinematics, K, B, and x0 were identified. Subsequently, these mechanical parameters were correlated with the above EMG variables. We found that equilibrium position and stiffness correlated significantly with the EMG variables processed as outlined above (r's: 0.55 - 0.8).
Referat in der Gruppe Psychomotorik II, Dienstag, 30. März 1999, 11:00, HS 20
