Quercetin supplementation increases muscle oxidative capacity and endurance in mice, but its ergogenic effect in humans has not been established. PURPOSE: To investigate the effects of short-duration chronic quercetin supplementation on muscle oxidative capacity; metabolic, perceptual and neuromuscular determinants of performance in prolonged exercise; and cycling performance in untrained men. METHODS: Using a double-blind, pretest-posttest control group design, 30 recreationally-active, but not endurance-trained, young men were randomly assigned to Quercetin (Q) and Placebo (P) groups. A noninvasive measure of muscle oxidative capacity (PCr recovery rate using magnetic resonance spectroscopy), peak oxygen uptake (VO_2peak), metabolic and perceptual responses to submaximal exercise, work performed on a 10-min maximal-effort cycling test following the submaximal cycling, and voluntary and electrically-evoked strength loss following cycling were measured before and after 7-16 d of supplementation with 1 g/d of quercetin in a sports hydration beverage or a placebo beverage. RESULTS: Pretreatment-to-posttreatment changes in PCr recovery time constant, VO_2peak, substrate utilization and perception of effort during submaximal exercise, total work done during the 10-min maximal effort cycling trial, and voluntary and electrically-evoked strength loss were not significantly different (P > 0.05) in Q and P. CONCLUSION: Short-duration, chronic dietary quercetin supplementation in untrained men does not improve muscle oxidative capacity; metabolic, neuromuscular and perceptual determinants of performance in prolonged exercise; or cycling performance. The null findings indicate that metabolic and physical performance consequences of quercetin supplementation observed in mice should not be generalized to humans.