The effect of stimulation frequency on the closed-loop control of quadriceps stimulation: Experimental results

Functional Electrical Stimulation (FES) is an important technique applied in rehabilitation of spinal cord injured individuals. When applied for restoration of movement, greater accuracy can be achieved if the stimulation is controlled with a closed-loop than an open-loop control strategy. However, closed-loop controller design for FES systems was historically proven to be non-trivial. The study reported in this article aimed at experimental verification of a newly developed sliding mode FES controller for knee joint angle tracking, The study was carried-out on two healthy and one spinal cord injured subjects. The emphasis of the study design was to evaluate the effect of stimulation frequency on the achieved movement tracking performance. Based on the obtained results it can be concluded that higher stimulation frequency leads to slightly, but statistically not significantly improved tracking performance. Optimal stimulation frequency with the respect to tracking performance and muscle fatigue appears to be between 30 and 40 Hz. Copyright (C) 2003 IFAC.