FES standing: control by handle reactions of leg muscle stimulation (CHRELMS).

Many paraplegics can stand using functional electrical stimulation (FES) of their extensor muscles without any modulation of the stimulus intensity by feedback. This is possible because, using handles and the intact upper-body muscles, the position of the pelvis can be controlled and this determines the positions of the two legs. Nevertheless, it is highly desirable that some practical method of modulating the stimulus intensities is used to reduce muscle fatigue and improve posture. We propose that the goal of the controller should be the minimization of the handle reaction forces by referring these forces to the equivalent leg joint moments and, as far as possible, making corresponding changes to the stimulation of the leg muscles. If force sensors are used only at the handles, the joint moments in the two legs are indeterminate. We hypothesize that in some patients acceptable results may still be obtained if we treat the two legs as one. This method will control standing up, standing, and sitting down; the user will be able to "feel" that his leg muscles are tiring and will be able to "posture switch" without any explicit instruction to the controller to change mode.