Long Term Effects of Fes-assisted Walking on Dynamic Stiffness of Spastic Ankle

Abstract The effects of long-term Functional Electrical Stimulation (FES) assisted walking on ankle dynamic stiffness were examined in spinal cord injured (SCI) subjects with incomplete motor function loss. A parallelcascade system identification method was used to identify intrinsic and reflex contributions to dynamic ankle stiffness at different positions with subjects instructed to remain relaxed. Intrinsic stiffness dynamics were well modeled by a linear second-order model relating intrinsic torque to joint position. Reflex stiffness dynamics were accurately described by a linear, third order model relating half-wave rectified velocity to reflex torque. We examined four SCI subjects before and after long-term use FES-assisted walking (>16 months). Both reflex and intrinsic stiffness decreased in FES subjects following FES-assisted walking, whereas they increased in the control subject. The results suggest that long-term FES-assisted walking may have therapeutic as well as rehabilitation applications, since its use appears to make spastic joint mechanics more normal.