The dietary supplement co-enzyme Q10 (CoQ10) is a potent antioxidant and a component of the electron transport chain which has been show to improve muscle metabolism and blood flow. PURPOSE: The purpose of this study was to determine the impact of CoQ10 supplementation on oxidative stress, muscle metabolism and muscle blood flow in older adults. METHODS: Fourteen older individuals (68.5±7.0 years) were tested 2 weeks post placebo (week 2) and 2 weeks post CoQ10 supplementation (week 4). During each testing session the participants performed a 12 s dynamic plantar flexion exercise during which medial gastrocnemius muscle PCr and pH were measured using 31P magnetic resonance spectroscopy. Muscle oxygen saturation and blood flow were simultaneously measured using near infrared spectroscopy. Post exercise venous blood samples were drawn to determine malondialdehyde level as an oxidative stress indicator. The placebo and CoQ10 dosage was 200 mg/day. Paired t-test was used to determine differences between trials. RESULTS: After 2 weeks of CoQ10 supplementation, no differences were observed in resting PCr (40.0±1.4 vs. 39.9±2.2 mM), or intracellular muscle pH (7.03±0.02 vs. 7.01±0.02). However, trends for improvements in metabolic, hemodynamic and oxidative stress status were observed (PCr recovery rate after exercise: 26.4±10.6 vs. 27.5±11.9 mM/kg/min; NIRT50: 55.8±43.1 vs. 50.7±30.6 s; post exercise malondialdehyde level: 1.7±0.8 vs. 1.4±0.4 uM/l). CONCLUSIONS: Our results show that there may be alterations in oxidative stress level as well as muscle metabolic and hemodynamic status with CoQ10 supplementation. Two weeks of CoQ10 supplementation at 200 mg/day, however, did not significantly impact these oxidative stress status, metabolic or hemodynamic measures. Based on the trends that were observed, higher doses or a longer supplementation period may be advisable for future research. (Support: Diabetes Action Research and Education Foundation)