Research
Mixed
Functional Overreaching (FOR) is a normal part of training that leads to performance improvement after recovery, whereas Non-Functional Overreaching (NFOR) and Overtraining Syndrome (OTS) involve prolonged maladaptation and performance decrements that take weeks or months to resolve.
Expect temporary performance dips during intense training blocks. This is 'Functional Overreaching' and is necessary for improvement. If the dip lasts weeks or months and is accompanied by mood disturbances or hormonal changes, it may be 'Non-Functional Overreaching' or 'Overtraining Syndrome,' requiring extended rest and medical evaluation.
StrongQualifiesHIGH confidence
This Functional Overreaching (FOR) will eventually lead to an improvement in performance after recovery. When athletes do not sufficiently respect the balance between training and recovery, Non-Functional Overreaching (NFOR) can occur... The athlete will often show the same clinical, hormonal and other signs and symptoms.
Why this rating
Consensus definition provided in the position statement.
Source
Prevention, diagnosis and treatment of the Overtraining Syndrome
Romain Meeusen et al. · European Journal of Sport Science · 2006
DOI 10.1080/17461390600617717
narrative_reviewCited 377×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Overtraining Syndrome (OTS) is diagnosed by excluding organic diseases and confounding factors (such as caloric restriction, iron deficiency, or infections) rather than by a single positive diagnostic marker, as no current test meets all diagnostic criteria.Strong
- Hormonal markers, such as the testosterone/cortisol ratio, are not reliable for diagnosing Overtraining Syndrome because they reflect acute physiological strain rather than the syndrome itself, and no single hormonal test is generally accepted.Strong
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