Reciprocal EMG control of elbow extension by FES

Elbow extension is critical in performing activities of daily living. Individuals with a C5-C6 spinal cord injury have paralyzed elbow extensors, yet retain weak to strong voluntary control of elbow flexion. Previous studies have shown that functional electrical stimulation (FES) of the triceps provides sufficient elbow extension strength and control to greatly improve function. With triceps stimulation applied at a constant level, elbow angle is controlled naturally by voluntary flexion opposing the stimulated extension-referred to as voluntary antagonist control. We have investigated an alternative reciprocal control scheme employing biceps electromyogram. (EMG) to modulate triceps stimulation. With reciprocal control, increasing biceps EMG proportionally reduces triceps stimulation. A personal computer (PC)-based lab system was designed to test the feasibility of reciprocal control. Reciprocal control increased the range of elbow moments, was stable during maintained elbow angle or isometric moment, and used less stimulation. Reciprocal control of triceps stimulation using biceps EMG is an effective method for restoring elbow extension to C5-C6 spinal cord injury patients, and could be extended to other situations where a voluntarily controlled muscle can be opposed by stimulating an antagonist.

I. Introduction

Functional electrical stimulation (FES) has restored motor function to individuals with spinal cord injuries [1]–[4]. Individuals with C5–C6 tetraplegia are left without voluntary control of upper and lower extremity muscles. Voluntary movements include elbow flexion, some shoulder movement, and, in C6, subjects wrist extension. An important group of muscles paralyzed at this level of injury is the elbow extensors. The elbow extensor muscles are important for reaching during activities of daily living. Although mechanical orthoses can compensate for the elbow extensor muscles [5], [6], FES provides a cosmetically acceptable solution making use of the patient's own muscles.