Dependence of elbow viscoelastic behavior on speed and loading in voluntary movements.

The objective of this study was to characterize the mechanical behavior of the elbow joint during voluntary movement, for different speeds of movement and under different loading conditions. Torque pulses of 50 ms duration were applied at movement onset and at peak velocity on random trials. The displacement away from the unperturbed trajectory was used as an indicator of the relative compliance of the elbow under different conditions. We found that both the displacement and the time taken to return to the unperturbed trajectory decreased if the overall speed of the movement increased or if a viscous resistive load was added, implying lower joint compliance. It was possible to account qualitatively for differences in mechanical behavior from observed muscle activation patterns.