Abstract
A system was developed to measure ankle joint viscoelasticity of human in upright posture as well as stretch reflex gain using step perturbation. The viscoelasticity was identified with the transient response before the onset of the stretch reflex, and the reflex gain was identified with the response after the visoelastic torque was subtracted. The role distribution among ankle joint viscoelasticity, stretch reflex and postural control system have been discussed using an inverted pendulum model and the identified parameters. It was revealed that the stretch reflex is inhibited in single-leg standing while the viscoelasticity and the postural control system increase their role in postural stability.
