Individuals with spinal cord injury (SCI) are at a lifelong risk of increasing obesity and several chronic metabolic disorders such as glucose intolerance, insulin resistance and dyslipidemia secondary to deterioration in body composition. Within few weeks of injury, there are significant decrease in whole body fat-free mass (FFM), particularly lower extremity skeletal muscle mass and subsequent increase in fat mass (FM). Resistance training (RT) is an important type of exercise that has been shown to induce positive physiological adaptations such as increasing lean mass and reducing metabolic disorders in other clinical populations. In a pilot work, we provided evidence that evoked RT using surface neuromuscular electrical stimulation (NMES) for knee extensor muscle group resulted in significant increase skeletal muscle cross-sectional area (CSA), reduction in % leg FM and a trend towards decrease in visceral adipose tissue (VAT) CSA. The favorable adaptations in body composition were associated with decrease in plasma insulin area under the curve and plasma triglycerides. We attributed the adaptations in body composition and metabolic profile to an associated increase in plasma insulin-like growth factor (IGF-1). We concluded that twelve weeks of evoked RT targeted towards evoking skeletal muscle hypertrophy could result in significant body composition and metabolic adaptations in individuals with SCI. It is unclear if a longer RT program greater than 12 weeks would provide additional benefits to veterans with SCI. It is also unknown whether enhancing the decline anabolic homeostasis by providing testosterone (T) replacement therapy (TRT) would reverse body composition and metabolic profile changes in veterans with SCI. The major research goal of this proposal is to investigate the effects of 16 weeks of evoked RT+TRT vs. TRT on body composition (muscle CSA, VAT, %FM) and the metabolic profiles (glucose and lipid metabolism) in individuals with motor complete SCI. To address this goal, surface NMES accompanied with ankle weights will be conducted twice weekly to exercise the knee extensor skeletal muscle groups from sitting position. After 4 weeks of delayed entry approach, participants (n =24) will be randomly assigned into RT+TRT (n =12) or TRT (n =12) groups. The TRT will be provided via transdermal T patches that will be alternated on both shoulders over the course of the study. We also propose to study the effects of detraining on body composition and metabolic profiles. The research plan includes three specific aims that were devised by the candidate and his mentors.
Specific aim 1 will demonstrate the effects of NMES RT and/or Testosterone patches (Tp) on the CSA of thighs and legs skeletal muscle groups, percentage FFM, and the CSA of VAT, intramuscular fat and percentage FM after 16 weeks of training+Tp and 16 weeks of detraining.
Specific aim 2 will determine the changes in metabolic milieu (resting energy expenditure, glucose homeostasis, lipid profile, free fatty acids, serum total and free testosterone and IGF-1), and cytokines (c-reactive protein, tumor necrosis factor alpha and IL-6 as inflammatory biomarkers) after 16 weeks of training+Tp and detraining.
Specific aim 3 will determine if 16 weeks of evoked RT and Tp will increase GLUT-4 concentration, muscle IGF-1 and peroxisome-proliferator-activated receptor-gamma co-activator 1 (PGC-1) expressions, altered fiber type distribution and enhance the mitochondrial enzymatic activities (electron transport chain) compared to Tp only.
The goal of this proposal is to investigate the efficacy of a complimentary approach of evoked resistance training and testosterone replacement therapy on the changes in body composition and metabolic profile after SCI. The proposed method could become a recommended and simple intervention especially for individuals with limited access and poor tolerance to exercise. The rationale is based on the evidence that individuals with SCI experience decline in anabolic hormones which may be responsible for the deterioration in body composition and metabolic profiles and leads to increase obesity, type 2 diabetes mellitus, dyslipidemia and subsequently cardiovascular disease. The designed study will provide explanation to the adaptations in the energy source of the muscle cells in response to training. The completion of the proposed experiment will allow the candidate to compete as an independent research investigator.