Functional Electrical Stimulation Closed-Loop Strategy Using Agonist-Antagonist Muscles for Controlling Lower Limb Movements

Abstract

Functional electrical stimulation (FES) has been used to rehabilitate people with spinal cord injury (SCI) because it allows the control of functional movements. This work presents a knee extension control strategy that uses closed-loop FES to produce controlled functional movements in people with SCI, operating on the agonist and antagonist muscle groups of the leg. The system involved a Raspberry Pi PI controller and an Atmega328 signal generator. The frequency response method has helped to find stable values to two adjustable parameters of the controller. A low-pass filter represented the volunteer’s leg. Stimulation on the quadriceps muscle group (agonist) and quadriceps combined with hamstrings muscle group (antagonist) were tested, and the latter allowed a more effective muscle control. The simplicity of the plant and the controller resulted in some undesirable behaviors such as oscillations, which could be circumvented by the variety of parameters made available by the frequency response method.