CYCLE-TO-CYCLE CONTROL OF SWING PHASE OF PARAPLEGIC GAIT INDUCED BY SURFACE ELECTRICAL-STIMULATION

Parameterised swing phase of gait in paraplegics was obtained using su rface electrical stimulation of the hip flexors, hamstrings and quadri ceps; the hip flexors were stimulated to obtain a desired hip angle ra nge, the hamstrings to provide foot clearance in the forward swing, an d the quadriceps to acquire knee extension at the end of the swing pha se. We report on two main aspects; optimisation of the initial stimula tion parameters, and parameter adaption (control). The initial stimula tion patterns were experimentally optimised in two paraplegic subjects using a controlled stand device, resulting in an initial satisfactory swinging motion in both subjects. Intersubject differences appeared i n the mechanical output (torque joint) per muscle group. During a prol onged open-loop controlled trial with the optimised but unregulated st imulation onsets and burst duration for the three muscle groups, the h ip angle range per cycle initially increased above the desired value a nd subsequently decreased below it. The mechanical performance of the hamstrings and quadriceps remained relatively unaffected. A cycle-to-c ycle controller was then designed, operating on the basis of the hip a ngle ranges obtained in previous swings. This controller successfully adapted the burst duration of the hip flexors to maintain the desired hip angle range.