Influence of biomechanical properties of the arm on end-point kinematics

Submovements in pointing movements have always been considered as a corrective mechanism that compensates for noise in arm motion and provides the required accuracy at the target. The purpose of the present study was to investigate whether the requirement to dissipate energy accumulated for the motion and the requirement to regulate interactive torque also causes submovements in pointing movements. With this purpose, the incidence of submovements was compared between discrete and reciprocal pointing movements in four directions. Energy dissipation is required during pointing in the discrete and not reciprocal mode. The four pointing directions provided manipulations with conditions for interactive torque regulation. To emphasize the accuracy requirement, the target size was also manipulated. The results supported the motion termination and accuracy demands but not interactive torque regulation as factors causing submovements. However, gross submovements (characterized by zerocrossings in the first two end-point displacement derivatives) served predominantly for motion termination, and fine submovements (characterized by zerocrossings in the third derivative of the end-point displacement profile) were primarily used to satisfy the accuracy demands. The study emphasizes the importance of the biomechanical factor in production of the kinematic characteristics of arm motion.