Feedback torque generation in human eigenvector coordinate

Abstract

Introduction:We formulated a hypothesis that torque generation could be described by independent eigenvector control. Methods:Human postural modalities, stereotyped responses,were obtained from the eigenvectors, and modal control input was determined by the linear combination of corresponding modality. To verify the model, postural responses subjected to fast backward perturbation were used. Upright posture was modeled as 3-segment inverted pendulum in sagittal plane, and feedback torque was designed to use each modality independently after the dynamic equation of motion was transformed into the eigenvector coordinate. We used optimization method to obtain eigenvector feedback gains to reproduce both joint angles measured from the postural response and joint torques calculated by inverse dynamics. Results: Independent eigenvector control showed a good fit ~0.8 in 3-segment simulation, and gain scaling in response to increased perturbations was observed in eigenvector feedback gains. Ankle feedback control decreased with the growing of perturbation magnitude, while hip feedback control increased to accommodate biomechanical constraints on allowable joint torque. Conclusions: The results suggest that human feedback response using torque generation might be explained by eigenvector control, and the scaling behaviors depending on perturbation magnitudes are showing change of postural strategies from ankle strategy to hip strategy.