Trajectories of Human Multi-Joint Arm Movements: Evidence of Joint Level Planning

In this paper we show that staggered joint interpolation [7] with maximaRy smooth joint motion can account for both the hand paths and tangential velocity profiles observed in human. multi-joint atm movements. Arm trajectories were recorded while subjects perfotmed point-to-point movements in a vertical plane. ‘Ihe shape of the tangential velocity profile of the hand was found to be symmeuica.l and belMqxd. Although this finding is predicted by the maximum-smoothness them-y 161, which assumes that hand motion is maxirnahy s,mooth. the theory cannot account for the curved hand paths which were often observed The present model assumes that joint motion, rather than the motion of the hand is maximaRy smooth. The results of this work suggest that multi-joint arm movements may be pianned at the joint level.