Fast movements of human arm: reflections on control issues

Fast extension trajectories of the arm and muscle EMG that were recorded for various amplitudes and loads are shown and discussed. Forearm trajectories are smooth, with bell-shaped speed profiles. The upper arm trajectories may have three segments, with the speed profile having two peaks. As one moves from central to peripheral points on the arm, the three segments merge together, producing smooth curves. The forearm may be modelled as a system with two inputs: (1) the elbow joint displacement, and (2) muscle force. The observed input patterns are coordinated to produce the fast but smooth motion with negligible overshoot. The results clarify the role of joint control of shoulder and elbow joints in fast movements