Improving valid and deficient body segment coordination to improve FES-assisted sit-to-stand in paraplegic subjects.

We investigated dynamic optimization as a tool to improve functional electrical stimulation (FES) assisted sit to stand transfers of paraplegic subjects. The objective would be to find optimal strategy for voluntary trunk movement, which would minimize hip, knee and ankle torques and demand minimal upper limb participation during the motion. Motion of the knee and the ankle were constrained by electrical stimulation. Motion capture (MOCAP) data, and signals from handle force sensors were acquired during FES-assisted rising motion of one paraplegic subject. Based on a 3 DOF dynamic model, we used an optimization algorithm in order to determine optimal trajectories in terms of minimizing joint torques for various conditions of force level applied to handles. Motion computed using the optimization process is compared with the one recorded during the experiment. Our results suggest that in order to minimize the sum of joint torques and arm effort participation, paraplegic patients should bend their body forward in order to use linear momentum of the trunk in sit off phase. This information can be used to design controller for closed-loop FES-assisted standing-up. The controller could use trunk motion to trigger legs stimulation in order to optimize body segment coordination.