Mitochondrial Capacity and Muscle Endurance in Individuals with Parkinson’s Disease

Introduction: Parkinson's disease (PD) is associated with loss of motor control and difficulty exercising. This study measured skeletal muscle mitochondrial capacity and endurance in individuals with and without PD using novel non-invasive methods. We hypothesized that individuals with PD will have decreased mitochondrial capacity, reduced oxygen recovery, and decreased endurance compared to controls. Methods: Eight participants with PD and nine healthy controls were tested. Mitochondrial capacity was measured as the rate of recovery of muscle metabolism after electrical stimulation using near-infrared spectroscopy (NIRS) and repeated short arterial occlusions. Oxygen recovery was measured as the half time of recovery of oxygen levels after 5 minutes of ischemia. Muscle endurance was determined from changes in twitch contraction acceleration during electrical stimulation at 2, 4, and 6 Hz. Results: Mitochondrial capacity was lower in individuals with PD compared to controls (1.5±0.1min-1 vs. 1.7±0.1min-1, p=0.02). Individuals with PD had slower oxygen recovery after ischemia compared to controls (8.9±2.3s vs. 5.4±0.8s, p=0.01). Endurance was not different between groups at 6 Hz (PD vs controls: 58±23% vs. 69±16%, p=0.34). The effect sizes for mitochondrial capacity and oxygen recovery were large (Cohen's d >0.8). The Cohen's d for endurance was 1.11. Conclusion: Individuals with PD had slight impairments in mitochondrial capacity and blood flow but did not have reduced muscle endurance. While our study suggests that muscle metabolic dysfunction may play a minor role in exercise intolerance in people with PD, it demonstrates the use of noninvasive technologies to evaluate muscle function in people with neurological disorders.