This systematic review aims to evaluate the impact of dysfunctional aspects of overtraining, specifically non-functional overreaching (NFOR) and overtraining syndrome (OTS), on psychological and cognitive functioning among elite athletes. Elite athletes face unique stressors, including rigorous training and persistent competitive pressures. However, previous reviews have not differentiated between athletic profiles, such as elite versus non-elite athletes. Following PRISMA guidelines, this systematic review searched four electronic databases for studies involving elite athletes aged 18 or older who had undergone interventions leading to NFOR or OTS and assessed psychological or cognitive outcomes. The methodological quality of the studies was evaluated. Out of 2232 articles, 11 studies were included: seven focused on OTS, three on NFOR, and two on both NFOR/OTS, involving 461 participants. All the studies assessed at least one psychological outcome, showing alterations in mood, stress, burnout, and fatigue among elite athletes experiencing NFOR or OTS. However, the available evidence on psychological well-being was limited and showed considerable heterogeneity. Evidence on cognitive outcomes was limited and focused mainly on the domain of cognitive inhibition. Impairments in cognitive inhibitory control may occur only in the context of OTS, while no clear deficits were observed in athletes experiencing NFOR. In conclusion, this review highlights the detrimental effects of NFOR and, especially, OTS on elite athletes' psychological and cognitive health, emphasizing the need for targeted research and effective strategies to support athletes` performance and well-being.
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