Biodynamic modeling, system identification, and variability of multi-finger movements

A forward dynamic model of human multi-fingered hand movement is proposed. The model represents digits 2–5 in manipulative acts as a 12-degrees-of-freedom (DOF) system, driven by torque actuators at individual joints and controlled using a parsimonious proportional–derivative (PD) scheme. The control parameters as feedback gains along with an auxiliary parameter to modulate the joint torque magnitudes and cross-coupling can be empirically identified in an iterative procedure minimizing the discrepancy between the model-prediction and measurement. The procedure is guided and computationally accelerated by pre-knowledge of relations between the parameters and kinematic responses. An empirical test based on real grasping movement data showed that the model simulated the multi-finger movements with varied inter-joint temporal coordination accurately: the grand mean of the root-mean-square-errors (RMSE) across trials performed by 28 subjects was 3.25°. Analyses of the model parameters yielded new insights into intra- and inter-person variability in multi-finger movement performance, and distinguished the less variable motor control strategy from much more variable anthropometric and physiological factors.