Angular momentum regulation during human walking: biomechanics and control

Motivated by biomechanical studies on human walking, we present a control strategy for biologically realistic walking based on the principle of spin angular momentum regulation. Using a morphologically realistic human model and kinematic gait data, we compute the total spin angular momentum at a self-selected walking speed for one human test subject. We find that dimensionless spin angular momentum remains small (S₁/(mass height velocity) < 0.02) throughout the gait cycle, and maximum whole body angular excursions within sagittal (<1°), coronal (<0.2°), and transverse (<2°) planes are negligible. These data support the hypothesis that spin angular momentum in human walking is highly regulated by the central nervous system, and that there exists a nonlinear coupling between ground reaction force, F~, center of mass position, r~_CM , and center of pressure location, r~_CP, or F~ = (FZ_{//ZCM)(r~CM -r~CP). We employ this relationship to rapidly generate biologically realistic CP and CM reference trajectories. Using an open loop optimization strategy, we show that biologically realistic leg joint kinematics emerge through the minimization of spin angular momentum and the total sum of joint torque squared, suggesting that both angular momentum and energetic factors are important considerations for biomimetic controllers.}