TRAJECTORY FORMATION OF VERTICAL ARM MOVEMENTS THROUGH A VIA-POINT - A LIMIT OF VALIDITY OF THE MINIMUM-JERK MODEL

The minimum-jerk model predicts the smoothest trajectory for a class o f human movements and so provides us with a kinematic measurement of s killed motor performance. To establish the limits of the model's valid ity, the predicted and experimentally defined movement trajectories an d the joint coordination were compared in two-joint arm movements, bri nging the hand from the initial position to the final position through a specified point (a via-point). Kinematic data of the movements were obtained through the SELSPOT system. The movement path, tangential ve locity, and coordinated change in positions of the shoulder and elbow joints evidently deviated from those predicted by the model. These res ults suggest that the minimum-jerk model is not valid for movements un der extreme conditions which are highly dependent on musculoskeletal d ynamics.