Characterization of the flexion-withdrawal reflex for use in stimulation-assisted SCI gait

Preliminary results from studying the flexion-withdrawal reflex of paraplegic (spinal-cord-injured) subjects elicited by electrical stimulation (ES) are presented, characterizing the reflex dependence on ES parameter values and the degradation of the reflex with periodic ES. The goal is to develop automatic control strategies for regulating hip and knee angles during the swing phase of gait. It was found that hip flexion angle varied directly with pulse duration (PD) and burst duration (BD) up to 700 ms. Response duration varied directly with BD, whereas movement latency varied inversely with PD. In one subject, when stimulus bursts were repeated every 5 s, the leg continued to advance for 34 steps using a 50-ms interpulse interval (IPI) stimulus burst compared with nine steps using a 10-ms IPI burst