Restoring unassisted natural gait to paraplegics via functional neuromuscular stimulation: a computer simulation study

A computer simulation of functional neuromuscular stimulation (FNS)-assisted bipedal gait shows that it is difficult, but possible, to attain undisturbed, level gait at normal speeds provided the electrically stimulated ankle plantarflexors exhibit near-normal strengths or are augmented by an orthosis, and at least seven muscle groups in each leg are stimulated. A combination of dynamic programming and an open-loop, trial-and-error adjustment process was used to find a suboptimal set of discretely varying muscle stimulation patterns needed for a 3-D, 8 degree-of-freedom dynamic model to sustain a step. An ankle-foot orthosis was found to be especially useful, as it helped to stabilize the stance leg and simplified the task of controlling the foot during swing. It is believed that the process of simulating natural gait with this model will serve to highlight difficulties to be expected during laboratory and clinical trials.