Carrard et al. 2022, Diagnosing overtraining syndrome: a scoping review

This scoping review of 30 independent studies (952 subjects: 328 with overtraining syndrome, 624 healthy controls) found no single biomarker that accurately distinguished overtraining syndrome from healthy athletes. Hormonal, psychological, immunological and metabolic markers were all examined; none performed reliably in isolation, and the authors confirmed that overtraining syndrome remains a diagnosis of exclusion requiring that anaemia, infection, thyroid dysfunction, low energy availability and depression be ruled out first. Evidence moderate.