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Abstract

Spinal cord injury (SCI) results in varying levels of physical impairment depending on injury severity. A common problem reported by individuals with SCI is increased muscle fatigue, which can negatively impact daily function and quality of life. Muscle fatigue is defined as an exercise-induced reduction in muscle force and arises from both central and peripheral fatigue in non-injured people. However, the physiology behind increased fatigue in SCI remains underexplored, especially in the upper limb muscles that this population particularly prioritizes in daily life. This thesis investigates these two types of muscle fatigue and recovery in the first dorsal interosseous (FDI) muscle, essential for hand grasp actions, in chronic, motor incomplete SCI. Central fatigue was assessed through voluntary activation (VA) using the interpolated twitch technique during an maximal voluntary contraction (MVC), while peripheral fatigue was evaluated by measuring evoked tetanic contractions at different stimulation frequencies (1-100Hz) to create a force-frequency (FF) curve. Muscle fatigue was induced using a 2-minute isometric index finger abduction MVC. Data were collected at baseline, immediately after fatigue, and during recovery at 5-, 10-, and 15-minute intervals post-fatigue. Results showed that central fatigue played a major role, with SCI participants experiencing a greater decrease in VA post-fatigue compared to controls. For peripheral fatigue, SCI individuals showing slightly increased muscle contractile output post-fatigue likely due to adaptive fibre type changes, but there were no significant differences between the two groups. During recovery, VA recovered more slowly in SCI, while both groups had similar recovery in FF. These findings suggest that central fatigue is the primary contributor to fatigue in SCI, and incorporating training to enhance VA through rehabilitation could improve muscle function.