Adaptive inverse optimal Neuromuscular Electrical Stimulation

Neuromuscular Electrical Stimulation (NMES) (also described as functional electrical stimulation (FES) in some scenarios) is a prescribed treatment for various neuromuscular disorders where an electrical stimulus is provided to elicit a muscle contraction. Barriers to the development of NMES controllers exist because the muscle response to an electrical stimulation is nonlinear and the muscle model is uncertain. Several recent adaptive control results have been developed to enable a stimulated limb to track a desired limb trajectory. Yet, feedback methods (especially adaptive and robust methods) have a potential for overstimulation that can lead to faster muscle fatigue. Efforts in this paper focus on the development of a first ever inverse optimal NMES controller that yields an optimal limb tracking result. That is, a controller is designed that achieves desired limb trajectory tracking while simultaneously minimizing a cost functional that is positive in the error states and stimulation input. The inverse optimal controller is examined through a Lyapunov-based analysis and simulations.