THE EFFECT OF LOWER LIMB NEUROMUSCULAR ELECTRICAL STIMULATION ON THE MUSCLE AND METABOLIC HEALTH AFTER ACUTE SPINAL CORD INJURY

Abstract

Spinal cord injury (SCI) is a devastating event with long-term consequences for individuals and their families. It causes immediate disruption to neuronal pathways, leading to paralysis and loss of muscle function below the injury level. A few weeks after the injury, there is a rapid decline in contractile activity, muscle mass, and cross-sectional area. This leads to muscle fiber degeneration and a shift towards a higher proportion of fast glycolytic fibers, which are more prone to fatigue and less efficient in energy utilization. Severe muscle atrophy in SCI is closely linked to metabolic dysfunction, affecting overall health and rehabilitation recovery. As muscle tissue declines, there is a corresponding drop in the rate at which the body burns calories and absorbs glucose. This increases the risk of metabolic complications such as obesity and insulin resistance, which is a hallmark of type 2 diabetes. Addressing both muscle atrophy and metabolic dysfunction is crucial in SCI rehabilitation, emphasizing the need for therapies targeting muscle and metabolic health simultaneously. Neuromuscular electrical stimulation (NMES) uses electrical impulses to induce muscle contractions, enhancing strength, circulation, and preventing atrophy. While NMES is widely used for chronic SCI, research on acute SCI is limited. Novel NMES protocols are needed to induce molecular adaptations that maintain muscle mass and a metabolically healthy phenotype early post-injury. This dissertation investigated the effects of a 2–5 week Comb-NMES intervention on muscle and systemic parameters, including glucose and insulin levels, lipid profiles, muscle signaling for glucose uptake, inflammation, and atrophy. Additionally, we analyzed changes in muscle fiber-type distribution and cross-sectional area in 20 SCI participants (C4-L1) aged 18-60 years, injured within 14 days, and classified as AIS A-C. The Comb-NMES protocol integrates high-frequency resistance and low-frequency aerobic training targeting the quadriceps. Low-frequency stimulation repetitively stresses muscles to enhance oxidative metabolism, increase mitochondrial function, and retain type I fibers. Simultaneously, high-frequency stimulation applies dynamic contractions to prevent atrophy and maintain type IIa fibers. Findings from this dissertation suggest that Comb-NMES may improve muscle adaptations and systemic metabolism. This supports its use in early SCI therapy to enhance muscle health and prevent long-term complications.