A control-theoretic approach for human postural control modeling

Although classically-adopted PID-cascade postural control schemes are adequate for describing effects of external disturbances acting on upright stance, it is shown in this article that they fall short to address the issue of voluntary motion due to the inherent instability of uncontrolled upright posture. A novel alternative, “hybrid cascade-feedback scheme,” is presented and shown to be equivalent to the PID-cascade scheme in terms of external disturbances but overcome its shortcomings related to voluntary motion. This proposed scheme is based on a well-established robust tracking and disturbance rejection control method. It can be modularly extended to cover multi-input-multi-output scenarios through employing state-space tools.