Physiologic aspects of spinal cord injury and functional neuromuscular stimulation.

Functional neuromuscular stimulation (FNS) has been demonstrated to restore purposeful movement to muscles paralyzed by spinal cord injury (SCI). It is hoped that this technique will ultimately improve rehabilitation by enabling skilled activities for paraplegics (e.g., walking) and quadriplegics (e.g., feeding oneself) to be accomplished regularly with safety and reliability. It is also expected that FNS exercise programs will lead to higher levels of health and fitness for SCI individuals. However, high fatigability of electrically stimulated paralyzed muscles may severely limit FNS applications. This fatigability is related to numerous factors, including the deteriorated condition of the paralyzed muscles and cardiopulmonary system, the nonphysiologic way in which these muscles are activated with FNS, and the probability that organ system adjustments that normally accompany voluntary exercise do not occur to the same extent with this peripherally induced exercise. More research is necessary to determine the mechanisms of fatigue for FNS exercise so that methods could be devised to increase resistance to fatigue. In addition, more research is necessary to substantiate the potential health and fitness benefits that have been stated for FNS exercise training.