Computer simulation of FES-assisted locomotion

The general objective of this research was to investigate the feasibility of unsupported near-normal looking locomotion through functional electrical stimulation (FES), using a forward dynamics simulation model. The model encompassed skeletal, heel-pad, muscle activation, and muscle contraction dynamics with force-length muscle properties that were measured in-vivo. The evaluation of the model showed that it was able to reproduce normal gait kinematics with optimized muscle stimulation profiles that showed similarities to electromyographic data from a neurologically intact subject. Implementing models of heel contact and vestibular feedback resulted in enhanced stability. The contribution of muscle properties to stability was further explored by applying perturbations to four models which differed in their actuator properties. The model which captured most of the characteristic behavior of human muscles showed remarkable resistance to both static and dynamic perturbations.

It was encouraging to find that on-off muscle stimulation profiles could produce smooth and near-normal looking gait kinematics, and that intrinsic muscle properties contributed substantially to intersegmental stability. However, global stability remained a problem. It appears that unsupported sustained locomotion would require more, and particularly more complex feedback control systems. Future work might be focused on identifying which combinations of sensory feedback, bracing and external support devices have potential to be successful in clinical applications of FES-assisted locomotion of paraplegic patients.