A bipedal, closed-chain dynamic model of the human lower extremities and pelvis for simulation-based development of standing and mobility neuroprostheses

Functional neuromuscular stimulation (FNS) can allow individuals with paraplegia to perform many activities that were previously difficult or impossible from the wheelchair. FNS of muscles of the lower extremities generate the muscle forces required to rise from a chair and assume a standing posture. Users of these standing neuroprostheses typically require substantial actions by the voluntary upper extremities to provide additional power for maintaining balance, largely eliminating the functional benefits of standing. As part of a larger effort to develop a neuroprosthesis for providing unassisted standing (i.e., without upper extremity interventions or significant external bracing), we have developed a three-dimensional, bilateral, closed-chain, dynamic model of the human lower extremities and pelvis. Simulations with this model will be used to study the effectiveness of various FNS control schemes prior to implementing any such systems in human subjects. In the current study, approaches for overcoming numerical simulation problems arising from the closed-chain nature of the model are presented. A simulation which combined a forward simulation of the model with a closed-loop feedback controller is also described. The encouraging results indicate that this model will be a valuable tool in the development of neuroprostheses for standing and mobility