Characteristic Movement.

Plots of typical position and velocity profiles representing arm movements made by a chronic stroke and an age-matched neurologically intact control subject while making arm movements at baseline, into a divergent force field (Fd), and into Fd with vibration (V). Compared to baseline trials, Fd increased instability at the target position. Tendon vibration appeared to improve stability at the target for both subjects as evidenced by decreased movement at the target position and decreased oscillation amplitudes in the tangential velocity data during the stabilization period. EMG data indicated that control subjects co-contract antagonist muscles and increase their grip in response to Fd. Stroke subjects, whose EMG and grip activity was already heightened during baseline trials were unable to invoke the same compensation.