Determination of Muscle Recruitment Sequences in Upper Limb while Reaching Tasks

Although muscle activation timing and its level while reaching movements in a two-dimensional horizontal plane have been extensively studied, the present study was designed to experimentally determine the muscle recruitment sequence (which muscle is a determinant of its activity level) using reaching tasks in the anterior-posterior and medial-lateral directions. The preferred torque directions in six upper limb muscles were calculated and referenced to determine the muscle recruitment sequences while anterior-posterior and medial-lateral reaching tasks. The results indicated that the estimation of muscle recruitment sequences using an inverse dynamics operation starting from the end-effector side for an anterior-posterior movement and a forward dynamics operation for a medial-lateral movement could reproduce the observed muscle activation patterns.