Ischemic Preconditioning to Augment muscle Function in Individuals with Spinal Cord Injuries

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Spinal cord injury (SCI) often results in a sedentary lifestyle and profound deconditioning due to limited options for exercise. This decreased physical activity often leads to weight gain, bone loss, muscle atrophy, poor circulation, impaired cardiovascular function along with depression and decreased self-confidence. Options to exercise the muscles below the level of injury are restricted to electrical stimulation driven exercise that is constrained to reduced muscular force and work output. This ultimately results in reduced cardiorespiratory, metabolic and muscular adaptations compared to volitional exercise interventions in able bodied individuals. For this reason, an intervention that can increase the muscular force and work performed during electrical stimulation (ES) exercise is of utmost importance for individuals with SCI as it can lead to improved maintenance of lower limb muscle mass, better physiological adaptations and improved quality of life. Ischemic preconditioning (IPC) consists of brief periods of ischemia followed by reperfusion performed prior to exercise. In the general population, IPC has shown positive muscular benefits such as increased aerobic and anaerobic exercise performance, prolonging the time to skeletal muscle fatigue and improved recovery from maximal effort. However, this promising intervention has yet to be tested with ES exercise in those with SCI. Thus, the purpose of this SPiRE proposal is to determine if IPC prior to exercise with ES is safe and can improve skeletal muscle function and endurance in Veteran’s with complete SCI. 20 subjects will be recruited for a study consisting of 5 sessions that will involve performing IPC or a sham prior to ES isolated muscle contractions or ES lower body exercise. Specific Aim 1 will determine the safety of performing an acute bout of IPC prior to performing knee extension and if maximal muscle strength and fatigue resistance (Biodex isokinetic dynamometer) improves after IPC. In addition, tissue oxygenation, femoral blood flow and blood lactate will be assessed to identify potential impact of IPC on tissue perfusion and vascular function. Specific Aim 2 will determine whether performing an acute bout of IPC prior to ES cycling exercise (cycling on a recumbent tricycle) will improve performance including power output and time/distance cycled. Tissue oxygenation, femoral blood flow and blood lactate will also be collected during these sessions. Ultimately, if an acute bout of IPC is safe and augments muscle performance during ES exercise, further studies to determine long-term physiological benefits of chronic ES exercise in combination with IPC would be warranted. IPC has the potential to enhance the current rehabilitation standards for Veterans with SCI. In addition the ability to increase exercise intensity and cycling performance has potential to provide Veterans with SCI the additional muscle strength required to cycle overground and in the community on modified trikes with ES.