Angular Velocity Profiles of Upper Limb Joint Synergies in Reaching Movements: a pilot study

The spatiotemporal kinematic synergy, a coupling of multiple degrees of freedom (DoF), runs through human activities of daily living (ADL). And it is an entry point for exploring the central nervous system's (CNS) control process of musculoskeletal system by analyzing the time-varying kinematic synergy. The aim of this study was to find more physiological properties from the angular velocity profiles of synergy. Ten healthy right-handed subjects were asked to reach target button at different locations. During reaching movement, the motion data of five right upper limb joints were recorded, and the synergistic patterns were extracted by PCA algorithm. Our results showed that the combinations of the first four synergies were sufficient to explain raw data. As far as possible to exclude the effects of individual and information differences, we found shoulder flexion/extension and elbow flexion/extension made distinct contribution in a period of time to the control procedure performed by CNS after targets were confirmed. Our preliminary results implied that reaching movements required comparatively constant scheduling of shoulder horizontal abduction/adduction, shoulder internal/external rotation and wrist ulnar/radial deviation by CNS, while scheduling of SFE and EFE depends on the objectives.Clinical relevance- The findings of this paper may provide a novel dynamic control evidence based on CNS for realizing near-natural control of assistive devices in motor rehabilitation area.