Biomechanical Modeling of Upper-Limb Inter-Joint Coordination: Contrasting Kinematic Synergies in Analytical and Functional Tasks

Wearable Inertial Measurement Units (IMUs) are suitable for kinematic analysis in uncontrolled environments. Nonetheless, modeling multi-joint coordination during the execution of functional tasks remains a challenge. In this study is presented a kinematic modeling approach for assessing upper-limb inter-joint kinematic coordination dynamics, designed to: (1) characterize the spatial variance structures and temporal variability during both isolated movements and functional Reach-to-Grasp (RTG) tasks and, (2) determine if these spatial kinematic synergies allow prediction of the stability of temporal coupling. For this purpose, thirteen healthy participants performed five predefined movements and an RTG task while monitored by four wireless IMUs (60 Hz). Joint kinematics were modeled using quaternions; spatial coordination patterns were extracted using Principal Component Analysis (PCA), and their inter-joint temporal stability was quantified via Continuous Relative Phase (CRP) variance. Kinematic analysis shows a high spatial variance of the structure during the evaluation of isolated analytical tasks (<!-- MathType@Translator@5@5@MathML2 (no namespace).tdl@MathML 2.0 (no namespace)@ -->