Quercetin supplementation increases muscle oxidative capacity and endurance in mice, but its ergogenic effect in humans has not been established. Our study investigates 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. Using a double-blind, pretest-posttest control group design, 30 recreationally active, but not endurance-trained, young men were randomly assigned to quercetin and placebo groups. A noninvasive measure of muscle oxidative capacity (phosphocreatine 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 days of supplementation with 1 g/day of quercetin in a sports hydration beverage or a placebo beverage. Pretreatment-to-posttreatment changes in phosphocreatine 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 the quercetin and placebo groups. 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.