Model-based development of a user control algorithm for postural control via a FES-based standing neuroprosthesis

The goal of this study was to devise an algorithm that would allow the user of a functional electrical stimulation (FES)-based neuroprosthesis to command desired transitions in body center of mass (COM) via smooth changes in lower extremity joint angles. Simulations were performed with a musculoskeletal model modified to reflect an individual with thoracic spinal cord injury, as well as the use of a 16 channel FES system. These simulations indicated useful subsets of 16 muscles, and a set of four polynomial surfaces were fit through the space relating COMx, COMy, and each of the four lower extremity joint angles studied. These polynomial surfaces provided a robust method for selecting a particular, smooth trajectory through this space. These results indicate that a 16-channel FES system should be capable of allowing users to shift postures over a significant fraction of the forward-backward range used by able-bodied individuals during typical activities.