Overtraining Syndrome and Hypothalamic-Pituitary-Adrenal Axis Dysfunction in Athletes: Mechanisms and Diagnostic Uncertainty - a narrative review
DOI:
https://doi.org/10.12775/QS.2026.78.76475Keywords
overtraining syndrome, hypothalamic-pituitary-adrenal axis, cortisol, testosterone-cortisol ratio, sports endocrinology, athlete monitoring, relative energy deficiency in sportAbstract
Background. Overtraining syndrome (OTS) is a maladaptive state arising from chronic imbalance between training/non-training stress and recovery, historically attributed to dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis. Despite decades of research, no validated biomarker or diagnostic threshold exists, and the directionality of HPA involvement remains contested.
Aim. To critically synthesise evidence on HPA-axis mechanisms in OTS, contrast them with competing pathophysiological hypotheses, and evaluate the diagnostic uncertainty limiting clinical recognition and management.
Materials and Methods. Narrative review of peer-reviewed English-language systematic reviews, cross-sectional and longitudinal cohort studies, case series, consensus statements, and mechanistic physiological studies addressing OTS, HPA-axis function, hormonal biomarkers, and related conditions in athletes.
Results. Basal cortisol and ACTH are generally unhelpful diagnostically, whereas stimulation-test responses (insulin tolerance test, two-bout exercise protocol) more consistently reveal blunted late hormonal reactivity in overtrained athletes, though findings remain inconsistent across cohorts. The testosterone-to-cortisol ratio, cytokine, glycogen, central-fatigue, autonomic, and gut-brain-axis hypotheses each explain fragments of the clinical picture without unifying explanatory power. Composite instruments (EROS-COMPLETE, EROS-SIMPLIFIED) show promising discrimination in small single-sex cohorts but lack external validation.
Conclusions. HPA-axis dysfunction in OTS is real but neither sufficient nor specific as a diagnostic criterion. Progress requires standardised stimulation-testing protocols, sex-inclusive cohorts, and multi-domain composite instruments rather than continued pursuit of a single biomarker.
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Copyright (c) 2026 Gabriela Sadurska, Marek Psiuk, Aleksandra Prusaczyk-Świerzewska, Oliwia Hunek, Karolina Gajewska, Natalia Januszewska, Piotr Matuszewski, Julia Ziółkowska, Aleksandra Kleparska, Igor Smędowski
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