Physiology of Functional Electrical Stimulation-Induced Exercise: Basic Science Perspective

Abstract

Although individuals with lower-limb paralysis due to spinal cord injury (SCI) usually use their arms for wheelchair locomotion and exercise training, several factors can cause rapid fatigue, including the relatively small muscle mass, deficient cardiovascular reflex responses and inactivity of the venous muscle pump (resulting in hypokinetic circulation). This makes it difficult to develop cardiopulmonary (aerobic) fitness and maintain an active lifestyle. This paper presents research related to functional electrical stimulation (FES) techniques to induce exercise in the paralyzed lower-limb musculature of SCI individuals, and to evaluate physiologic responses with respect to improving health, physical fitness, and rehabilitation potential. FES techniques presented are: rhythmic isometric contractions to promote venous return, weight training exercise, leg cycle ergometer exercise, and simultaneous FES leg cycling and voluntary arm cranking exercise. Advantages of FES exercise include activation of a large muscle mass that is usually dormant, and improved peripheral and central hemodynamic responses. Studies suggest that chronic FES exercise training can result in physiologic adaptations to increase muscle strength and endurance, as well as to improve cardiopulmonary fitness. This involuntary exercise mode appears to be especially advantageous for quadriplegics.