Upper Limb Joint Angular Velocity Synergies of Human Reaching Movements

Understanding how the central nervous system copes with the high number of degrees of freedom in the musculoskeletal system is an open challenge. A possible approach is that the CNS uses kinematics and neuromuscular synergies as neural strategies for movements to reduce the complexity of control. The present study aims at analyzing the kinematics complexity of human arm movements, and determining kinematics synergies in upper-limb movements. Four right-handed subjects executed ten tasks involving movements on three directions (contralateral, central, and ipsilateral) while sitting in front of a cardboard. A motion capture system was used to record subjects' data during each task, to evaluate angular velocities of shoulder flexion, abduction, internal rotation, and elbow flexion. The kinematics synergies were derived from tasks using Principal Component Analysis for each subject. Results showed that the first three Principal Components captured approximately 86% of the variance, and the first six PCs accounted for 96%. The synergies were then used to reconstruct each task, featuring a normalized reconstruction error of 0:28% for the first three synergies recruited. The findings of this study might provide simplified strategies for design and control of wearable artificial limbs for rehabilitation-based therapies.<bold> </bold>