Development of a closed-loop controller for functional electrical stimulation therapy plus visual feedback balance training for standing balance training

Individuals with incomplete spinal cord injury (iSCI) demonstrate impaired upright balance, resulting in increased fall risk. Task-specific visual feedback balance training (VFBT) has previously been shown to improve upright balance. In addition, therapies using functional electrical stimulation (FES) have been shown to improve various motor functions. Combining VFBT with FES therapy (FES+VFBT) may synergistically improve balance control for those with iSCI. Here we developed the FES+VFBT system that delivered physiologically relevant electrical stimulations to soleus (SOL) and tibialis anterior (TA) muscles during VFBT. Ten young able-bodied individuals participated. Kinematic, kinetic, SOL and TA electromyography (EMG) data during quiet standing and limits-of-stability test were used to design the controller for the FES+VFBT system. To evaluate the performance of the designed controller, the controller outputs, which represented stimulation intensities, were compared with the recorded SOL and TA EMG during the four tasks associated with VFBT (i.e., bullseye, hunting, colour-matching, and ellipse tasks). Except for the bullseye task, the designed controller outputs were highly correlated with the recorded EMG, suggesting that the controller could generate electrical stimulations in a physiological manner. We expect that the addition of FES therapy to VFBT could contribute to improving standing balance for individuals with iSCI.