In human locomotion, we continuously modulate joint mechanical impedance of the lower limb (hip, knee, and ankle) either voluntarily or reflexively to accommodate environmental changes and maintain stable interaction. Ankle mechanical impedance plays a pivotal role at the interface between the neuro-mechanical system and the physical world. We characterized human ankle mechanical impedance in two degrees-of-freedom simultaneously using an ankle exoskeleton robot, the Anklebot. Static, dynamic impedance at rest posture and time-varying impedance during walking were estimated in previous studies, and we are extending the work towards rehabilitation.
Lee, Hyunglae, Hermano Igo Krebs, and Neville Hogan. “Multivariable dynamic ankle mechanical impedance with active muscles.” IEEE Transactions on Neural Systems and Rehabilitation Engineering 22.5 (2014): 971-981.