Application of the minimum jerk model to formation of the trajectory of the centre of mass during multijoint limb movements.

Abstract

Smoothness of movement is an inherent characteristic of the motor repertoire of primates. According to the minimum hand jerk model, a major feature of motor coordination in two-joint upper limb movements by humans in the horizontal plane is the production of the smoothest possible movement of the end effector, the hand ('hand version'). In the present study, this model was extended to the formation of the trajectory of the centre of mass (CMt) of the whole arm system ('CMt version'), and its importance for the shaping of multijoint movements was tested against the classical 'hand version'. During point-to-point movements between many pairs of targets in the work space, the movements of the CMt showed lower changes of torque than in movements of the hand on a straight path. Furthermore, the CMt version of the minimum jerk model reproduced the curved hand trajectory that can be observed in actual human performance. Under the assumption that the smoothness criterion is induced by a high-level motor coordination, our results suggest that CMt-based planning can be an alternative strategy for joint coordination. It offers the advantage of the simplified scaling of joint torques which are suitable for execution of planned movements.