Quercetin in Endurance Training: A Review of Its Antioxidant and Fatigue-Resisting Properties

Quercetin, a ubiquitous dietary flavonoid, has garnered significant scientific interest for its potential as an ergogenic aid in endurance sports. This interest is predicated on robust preclinical evidence demonstrating its potent antioxidant, anti-inflammatory, and mitochondrial biogenesis-stimulating properties. However, a persistent disconnect remains between promising laboratory findings and the equivocal, inconsistent, and often modest results reported in human trials with athletes. This review critically and systematically evaluates the scientific literature concerning quercetin's purported antioxidant and fatigue-resisting properties in the context of endurance training. We dissect the primary molecular mechanisms through which quercetin is proposed to act, including the activation of the nuclear factor erythroid 2–related factor 2 (Nrf2) antioxidant response pathway, modulation of the peroxisome proliferator–activated receptor-gamma coactivator-1α (PGC-1α)/sirtuin-1 (SIRT1) axis for mitochondrial biogenesis, and inhibition of the nuclear factor kappa-light-chain-enhancer of activated B cells inflammatory signaling cascade. The core of this review is a critical analysis of the human performance and recovery data, juxtaposing studies that show benefit with those that report null effects. We synthesize the key controversies that dominate the field, focusing on the critical confounding roles of poor bioavailability, participant training status, supplementation dosage, and timing. The evidence suggests that quercetin's most reliable effects may lie in accelerating recovery from exercise-induced muscle damage (EIMD) and reducing soreness, rather than directly enhancing maximal endurance performance. Its primary value may be as a “training adaptogen” that modulates cellular stress responses, thereby improving fatigue resistance over time. We conclude that quercetin's poor oral bioavailability is the principal barrier that has likely confounded the majority of human research to date. Future research must prioritize the use of high-bioavailability formulations to definitively ascertain whether the impressive preclinical benefits of quercetin can be translated into meaningful, practical applications for endurance athletes.