Biomechanical sit-to-stand movement with physiological feedback latencies

Human biomechanical movements are complex physiological tasks efficiently regulated by the central nervous system (CNS). Proprioceptors (muscle spindles) provide feedback of fascicle length and velocity from a joint to CNS, which then control the entire movement. These feedbacks have delays which are accounted for by the required output command. In this study, we are using a four-link sagittal plane nonlinear biomechanical model with three joint angles, to simulate human sit-to-stand (STS) movement in the presence of these physiological latencies. Ankle, knee and hip joint angles have delays for angular and velocity feedbacks. We linearize the whole model using padé approximation which results in eighteenth order linear system. Then, we subject this system to optimal controller design scheme for three joint torques using eighteenth order compensator with physiological cost optimization. We provide simulation results for linear and nonlinear models which show the suitability of this scheme for further analysis of STS task, feedback latencies and their effects on controller gains.