Human postural feedback response described by eigenvector

Abstract

Human postural responses appeared to have stereotyped modality, such as ankle mode, knee mode, and hip mode in response to various perturbations. We examined whether human postural control gain of full-state feedback could be decoupled along with the eigenvector. To verify the model, postural responses subjected to fast backward perturbation were analyzed. Upright posture was modeled as 3-segment inverted pendulum incorporated with feedback control, and joint torques were calculated using inverse dynamics. Postural modalities, such as ankle, knee, and hip mode, were obtained from eigenvectors of biomechanical model. As oppose to the full-state feedback control, independent eigenvector control assumes that modal control input is determined by the linear combination of corresponding modality. We used optimization method to obtain and compare the feedback gains for both independent eigenvector control and full-state feedback control. As a result, we found that both feedback gains of two control models that fit the joint angle and joint torque data are reasonably closed each other, especially at the joint angle feedback gains. This implies that the simple parameterization using eigenvectors may be used to correlate the feedback gains of full-state feedback control, and this concept could be applied to explain torque feedback mechanism ruled by central nervous system.