Sequential segmental neuromuscular stimulation: An effective approach to enhance fatigue resistance

Electrical stimulation of skeletal muscle flaps is used clinically in appli cations that require contraction of muscle and force generation at the reci pient site, for example, to assist a failing myocardium (cardiomyoplasty) o r to reestablish urinary or fecal continence as a neo-sphincter (dynamic gr aciloplasty). A major problem in these applications (muscle fatigue) result s from the nonphysiologic manner in which most of the fibers within the mus cle are recruited in a single burst-like contraction. To circumvent this pr oblem, current protocols call for the muscle to be put through a rigorous t raining regimen to transform it from a fatigue-prone to a fatigue-resistant state. This process takes several weeks during which, aside from becoming fatigue-resistant, the muscle loses power and contraction speed. This study tested the feasibility of electrically stimulating a muscle flap in a more physiologic way; namely, by stimulating different anatomical par ts of the muscle sequentially rather than the entire muscle all at once. Se quential segmental neuromuscular stimulation (SSNS)allows parts of the musc le to rest while other parts are contracting. In a paired designed study in dogs (n = 7), the effects of SSNS on muscle fatigability and muscle blood perfusion in gracilis muscles were compared with conventional stimulation: SSNS on one side and whole muscle stimulation on the other. In SSNS, electr odes were implanted in the muscles in such a way that four separate segment s of each muscle could be stimulated separately. Then, each segment was sti mulated so that part of the muscle was always contracted while part was alw ays resting. This type of stimulation permitted sequential yet continuous f orce generation. Muscles in both groups maintained an equal amount of conti nuous force. In SSNS muscles, separate segments were stimulated so that the duty cycle for any one segment was 25, 50, 75, or 100 percent, thus varyin g the amount of work and rest that any segment experienced at any one time. With duty cycles of 25, 50, and 75 percent, SSNS produced significantly (p < 0.01) enhanced resistance to fatigue. In addition, muscle perfusion Was significantly (p < 0.01) increased in these sequentially stimulated muscles compared with the controls receiving whole muscle stimulation. It was concluded that SSNS reduces muscle fatigue and enhances muscle blood flow during stimulation. These findings suggest that using SSNS in clinica l myoplasty procedures could obviate the need for prolonged training protoc ols and minimize problems associated with muscle training.