Synthesizing Redundancy Resolution Criteria of the Human Arm Posture in Reaching Movements

The aim of this work is to characterize the regularity and variability of human arm movements. The arm posture is quantified by a swivel angle that is experimentally measured when a healthy subject is reaching for targets in a spherical workspace. It is shown that without specific instruction, a subject moving his/her arm tends to use a consistent arm posture with small variations when reaching the same target position, regardless of whether the subject is moving toward or away from the target. This observed posture consistency indicates that human motor control chooses a unique arm posture associated to a 3D hand position. From the perspective of posture consistency, this work further examines the posture predictions based on two hypotheses on human arm control strategies: one that maximizes the movement efficiency towards the head, particularly toward the mouth; and the other that minimizes the power consumption in joint space. The arm posture predictions based on these two control strategies are compared and the prediction errors for each control strategy are analyzed.