Components of the end-effector jerk during voluntary arm movements

Jerk (time derivative of acceleration) of the endpoint of a multi-joint kin ematic chain can be represented as the sum of terms related to jerks, accel erations, and velocities in individual joints. We investigated the relative contribution of these terms during simulations of planar movement of a 3-s egment kinematic chain and also during unconstrained movements at different velocities, over different amplitudes, and with different intentionally ch anged curvature. Our results demonstrate that the term related to individua l joint jerks dominates in the total endpoint jerk. This domination was par ticularly strong during voluntary movements and was not as striking during the simulations based on 5th-order polynomial functions for individual join t trajectories. Thus, the minimum-jerk criterion for multi-joint movements can be well approximated by minimization of the jerk-related terms for indi vidual joints. The decomposition of endpoint jerk into its terms shows pote ntial limitations of the commonly used 5th-order polynomial modeling for de scribing voluntary multi-joint movements.