Abstract
Goal-directed aiming movements are organized to be energy optimal. This strategy has typically been demonstrated as an undershoot bias in the primary sub-movement endpoint location, particularly in conditions where corrections to target overshoots must be made against gravity (e.g. Lyons et al., 2006). This pattern of result is also true for the organization of joint movement, where angular displacements in the joints responsible for moving larger masses are minimized (Fisher et al., 1997). In order to determine whether performers maintain these energy optimal behaviours amidst changes in task constraints, participants performed aiming movements to near, middle and far targets in both the up and down directions. Movements to these targets were performed with the index finger, as well as with short and long rod extensions to the index finger. By ÔÇ£lengtheningÔÇØ the end effector, it was hypothesized that performers would minimize angular displacements in the shoulder and elbow, since these joints were responsible for moving the largest masses. Consistent with this hypothesis, when moving to the far targets, primary sub-movements undershot the target to a greater extent when moving downward when compared to moving upward. Furthermore, as rod length increased, shoulder elevation was minimized in movements to the far up target and elbow extension was minimized in movements to the far down target. These results suggest energy optimization as a mediator of movement.Acknowledgments: NSERC, Queen Elizabeth II Science & Technology, Anne Poucher Scholarship