Your Basic Trainer

Library / Training principles

Overtraining

Also called overtraining syndrome, overreaching, functional overreaching, non-functional overreaching, unexplained underperformance syndrome

What research says happens when recovery falls short of training. How consensus statements define overreaching and overtraining syndrome, how studies try to spot them, and where the evidence is thin.

Region
Across the body
Updated
October 8, 2026
Reviewed
October 8, 2026 · how entries are checked

What it is

Research uses three terms for what can follow hard training, set out below2. A key source is a 2013 consensus statement from the American College of Sports Medicine and the European College of Sport Science1. It says non-functional overreaching can occur when the balance of training and recovery is not respected enough1.

Three states, named by what happens next

  • Functional overreaching. The 2013 statement describes a short-term drop in performance, without severe psychological or other lasting negative symptoms1. It leads in the end to better performance after recovery1.
  • Non-functional overreaching. A 2012 review tabulates the European college’s terms and gives this one as intense training that leads to a longer drop in performance2. Full recovery follows rest, and psychological or neuroendocrine (nerve and hormone system) symptoms increase2.
  • Overtraining syndrome. The same table gives it as consistent with extreme non-functional overreaching, but with more severe symptoms and maladapted physiology2. It adds a further stressor that other disease does not explain2.

How long each state lasts, in two reviews

Two reviews attach time frames to the three states, and their cut-offs differ2,4.

State2012 review, tabulating the European college’s terms2022 review
Functional overreachingPerformance drop lasting days to weeks2Usually up to 2 weeks4
Non-functional overreachingWeeks to months2Usually up to 3 to 4 weeks4
Overtraining syndromeMore than 2 months2Likely when reduced performance lasts more than 3 to 4 weeks4

Why the two longer states are hard to tell apart

The 2013 statement calls the line between non-functional overreaching and overtraining syndrome very difficult to draw1. It depends on the clinical outcome and on ruling out other causes1. Athletes often show the same signs and symptoms in both1.

A 2012 review says non-functional overreaching and overtraining syndrome differ in time to recovery, not necessarily in degree or type of symptoms2. Often they can be told apart only after a period of complete rest2. The review calls the symptoms of both varied, nonspecific, anecdotal and numerous2.

Triggers and other causes

The 2012 review lists potential triggers of overtraining syndrome2. They include more training load without enough recovery, monotony of training and too many competitions2. They also include sleep disturbances, stress from personal life or work, and earlier illness2.

The 2013 statement describes one way to understand where the syndrome comes from: rule out other explanations and find the triggers1. The things to rule out include disease, infection, eating too few calories, low iron and allergies1.

How it is measured

The 2013 statement says several kinds of marker are in use, from hormones to performance and psychological tests1. It says no marker meets the full set of criteria needed for general acceptance1. A 2016 International Olympic Committee consensus statement looked at markers of the syndrome’s onset5. It says no marker, in use or suggested, meets the full set of criteria for a reliable one5.

Performance

A 2020 systematic review covered 22 studies that used resistance exercise to try to bring on overreaching or overtraining in healthy people6. It concluded that a sustained drop in performance is the one marker established as reliable for overtraining in resistance exercise6.

A 2021 systematic review of 12 papers looked at trained to professional endurance athletes7. Changes in power output, heart rate and rating of perceived exertion (a score for how hard effort feels) reflected functional overreaching7. Changes in maximal oxygen uptake and heart rate variability (how much the time between heartbeats changes) did not7.

Questionnaires and self-reports

A 2016 systematic review covered 56 studies that measured athlete well-being both subjectively and objectively8. Subjective measures, such as mood and perceived stress, tracked short-term and long-term training loads more sensitively and consistently than objective measures8.

In the 2021 endurance review, scores on two questionnaires also reflected functional overreaching7. The page on listening to your body covers perceived exertion more widely7.

Heart rate

A 2008 meta-analysis looked at heart rate and heart rate variability after overload training in competitive athletes9. Its authors concluded that the changes were small to moderate and may fall within day-to-day variation9.

A 2016 systematic review and meta-analysis studied endurance-trained athletes10. Heart rate variability and heart rate recovery after exercise rose when training improved performance, and also in response to overreaching10.

Hormones and blood

  • Hormones. A 2017 systematic review of 38 studies compared athletes with overtraining syndrome or overreaching against healthy athletes11. Resting hormone levels were mostly normal11. Stimulation tests, mainly maximal exercise, showed blunted responses of growth hormone and of ACTH, another hormone11.
  • Blood markers. A 2018 systematic review and meta-analysis covered 59 studies of resting biomarkers (measurable signs in the body) in well-trained male athletes12. Many biomarkers changed with harder training, but not in a way related to changes in exercise performance12.
  • A two-bout exercise test. One study tested 10 underperforming athletes13. Later, 5 were classed as non-functionally overreached and 5 as having overtraining syndrome13. Two hormone responses to the second of two maximal bouts were much higher in the overreached athletes13. The authors said more data were needed before the test could serve as a gold standard13.

A 2025 study at one sports medicine clinic studied 110 athletes and recreational exercisers identified with overtraining syndrome14. It compared them with 447 healthy controls14. Fatigue, dizziness and shortness of breath were significant predictors of the syndrome14. So were lower maximal oxygen uptake and lower peak blood lactate14.

What studies found

How common it is

There is no sound figure for how common overtraining syndrome is: a 2012 review says exact prevalence and incidence data are lacking2. It says the syndrome appears to be extremely rare2. A 2016 article says overreaching is common in athletes, with reported incidence from 5% to 60%15. It says overtraining syndrome is much less prevalent15.

The figures that exist come from surveys in which athletes reported their own history16,17,18:

  • In 376 young English athletes (mean age 15) across 19 sports, 110 (29%) reported having been non-functionally overreached or overtrained at least once16.
  • In 272 young elite Swedish athletes from 16 sports, 37% reported having been “stale” at least once17.
  • A web survey drew 605 responses from competitive athletes in sports with a large resistance-training part18. They were a convenience sample (people who were easy to reach)18. About 71% reported an unexplained drop in performance18.

In the resistance-training survey, the most common length of the drop was 1 week to 1 month, reported by 43.8% of those affected18.

Training load was not the whole picture in three surveys

In a survey of 376 young English athletes, training load did not significantly predict who reported being non-functionally overreached or overtrained16. Its authors concluded that physical and psychosocial factors both contribute16. The Swedish study’s authors concluded that staleness was related to stressors outside training as well as to physical training17. In the resistance-training survey, 92.5% of reported episodes came with added stressors outside training18.

In strength training

A 2020 scoping review of 47 records covered strength sports and resistance training19. It found that short periods of high-volume or high-intensity lifting can produce functional overreaching19. It also found evidence that the same training kept up long term can lead to the non-functional kind19. The same review found minimal evidence that true overtraining syndrome has occurred in strength sports or resistance training19.

What overreaching came with in training studies

  • Smaller gains after a taper (a planned cut in training). In a study of 33 trained male triathletes, 23 did 3 weeks of overload training20. Of those, 11 were classed as functionally overreached and 12 as acutely fatigued without being overreached20. During the 4-week taper, the acutely fatigued group reached a higher peak performance than the overreached group20.
  • More reported infections. A randomised study of 27 trained male triathletes included 3 weeks of overload training21. Upper respiratory tract infections were reported by 67% of those classed as functionally overreached21. The figure was 22% in the acutely fatigued group and 11% in controls21.
  • Slightly less efficient sleep. A 2024 systematic review and meta-analysis covered 14 studies of overreaching from endurance-based training22. Sleep efficiency measured by actigraphy (a worn movement sensor) fell by 2.0%, with no effect on subjective sleep quality22. The review rated no included study as low in risk of bias22.

How long it lasts

The evidence on time course is thin: two reviews and two very small studies23,24,25,26.

  • A 2004 review says recovery from overreaching takes about 2 weeks23. It says recovery from overtraining syndrome is considered to take months to years23.
  • A 1998 review says symptoms normally resolve in 6 to 12 weeks, given very careful exercise and strategies for regeneration24. It says they may continue much longer24.
  • In a 2021 study, 12 athletes with overtraining syndrome followed a 12-week protocol25. It combined more calories, a break from training, better sleep and stress management25. Afterwards they showed a mix of no, partial and full recovery across the measures25.
  • A 2025 case series described three runners identified with overtraining syndrome26. After a mandated stop in training and then active recovery strategies, two of the three returned to competition26.

What is disputed

Whether the syndrome is a worse form of overreaching

The 2013 statement says it is generally thought that the syndrome’s symptoms are more severe than those of non-functional overreaching1. It adds that no scientific evidence confirms or refutes this1. A 2016 article reports disagreement over whether the two lie on a continuum15. The other view is that a separate stressor triggers the syndrome in an athlete who is already overreached15. A 2004 review found no evidence beyond anecdote that overreaching comes before overtraining, and suggested the continuum may be too simple23.

How weak the evidence base is

A 2022 systematic review looked for studies of adult athletes that met three tests3. Each had to record performance from before the syndrome began, show it held down for more than 4 weeks, and record psychological symptoms3. It found no such study, and concluded that the evidence base for understanding the syndrome in athletes lacks sufficient scientific quality3.

A 2012 review concluded that the syndrome is identified clinically, and that its definitions are arbitrary2. It said most past research studied athletes with overreaching and not the syndrome2. The same review says bringing on the syndrome in athletes on purpose would be unethical, and its origin is uncertain2. So, it says, there are no evidence-based means of avoiding it2. A 2022 review notes that female athletes are underrepresented in studies of the syndrome4.

Whether functional overreaching is needed

A 2020 review says functional overreaching is often brought on by design in endurance athletes, on the view that performance gains need it27. Some recent studies found smaller adaptations in overreached athletes than in athletes who did the same programme without overreaching27. Other studies found substantial gains in overreached athletes27.

Whether training is the cause at all

A 2015 review says the UK has adopted the term unexplained underperformance syndrome in place of overtraining syndrome28. The term reflects that the syndrome has many contributing causes28. Training load out of balance with recovery may not be the primary cause of underperformance28.

A 2022 review traces low energy availability (too little energy from food left for the body’s needs) to low intake, high expenditure or both29. The sources disagree on how much of overtraining it explains30,31:

  • A 2021 narrative review looked at overload and overtraining studies that had also measured energy or carbohydrate intake, or energy use30. In 18 of 21, there were signs of reduced energy or carbohydrate availability during the overload period30. Its authors argue that many negative outcomes of training overload may be mainly due to under-fuelling mistaken for overtraining30.
  • A 2022 systematic review and meta-analysis of training blocks of 2 weeks or more found 14 groups of athletes who underperformed31. Half also showed two or more markers of low energy availability31. Its authors concluded that overreaching is also seen without those markers, and that underperformance does not require low energy availability31.
  • A 2019 study compared 14 athletes with overtraining syndrome and 25 healthy athletes32. Training patterns were similar in the two groups32. Intake of carbohydrate, protein and total calories per day was each independently associated with the syndrome32.

A 2023 International Olympic Committee consensus statement covers relative energy deficiency in sport (REDs), and says low energy availability is its underlying cause33. It says REDs and overtraining syndrome each lack a single validated biomarker, and that their symptoms overlap in a complex way33. Each, it says, is identified by excluding other causes33. The statement says low energy and low carbohydrate availability, though hard to assess, should be excluded before symptoms are labelled overtraining syndrome33. It also cites a narrative review of overtraining syndrome studies, and says those studies may have shown REDs outcomes instead33.

Connections

Overtraining research starts from the balance between training and recovery1. The training side is covered under progressive overload and training volume: a 2020 scoping review linked high-volume or high-intensity resistance training with overreaching19. The recovery side is covered under rest and sleep: a 2012 review lists sleep disturbances among the potential triggers2. Self-report measures are also part of listening to your body8.

Low energy availability also bears on bone: a 2022 review calls it a major risk factor for bone stress injury29. The stress fracture page covers that injury29.

Overtraining is related to

Overtraining has been studied in

Sources

  1. Meeusen R, Duclos M, Foster C, Fry A, Gleeson M, Nieman D, Raglin J, Rietjens G, Steinacker J, Urhausen A (2013). Prevention, Diagnosis, and Treatment of the Overtraining Syndrome. Medicine and science in sports and exercise. doi:10.1249/MSS.0b013e318279a10a PMID 23247672
  2. Kreher JB, Schwartz JB (2012). Overtraining Syndrome. Sports health. doi:10.1177/1941738111434406 PMID 23016079
  3. Weakley J, Halson SL, Mujika I (2022). Overtraining Syndrome Symptoms and Diagnosis in Athletes: Where Is the Research? A Systematic Review.. International journal of sports physiology and performance. doi:10.1123/ijspp.2021-0448 PMID 35320774
  4. Carrard J, Rigort AC, Appenzeller-Herzog C, Colledge F, Königstein K, Hinrichs T, Schmidt-Trucksäss A (2022). Diagnosing Overtraining Syndrome: A Scoping Review.. Sports health. doi:10.1177/19417381211044739 PMID 34496702
  5. Schwellnus M, Soligard T, Alonso JM, Bahr R, Clarsen B, Dijkstra HP, Gabbett TJ, Gleeson M, Hägglund M, Hutchinson MR, Janse Van Rensburg C, Meeusen R, Orchard JW, Pluim BM, Raftery M, Budgett R, Engebretsen L (2016). How much is too much? (Part 2) International Olympic Committee consensus statement on load in sport and risk of illness.. British journal of sports medicine. doi:10.1136/bjsports-2016-096572 PMID 27535991
  6. Grandou C, Wallace L, Impellizzeri FM, Allen NG, Coutts AJ (2020). Overtraining in Resistance Exercise: An Exploratory Systematic Review and Methodological Appraisal of the Literature.. Sports medicine (Auckland, N.Z.). doi:10.1007/s40279-019-01242-2 PMID 31820373
  7. Roete AJ, Elferink-Gemser MT, Otter RTA, Stoter IK, Lamberts RP (2021). A Systematic Review on Markers of Functional Overreaching in Endurance Athletes.. International journal of sports physiology and performance. doi:10.1123/ijspp.2021-0024 PMID 34108275
  8. Saw AE, Main LC, Gastin PB (2016). Monitoring the athlete training response: subjective self-reported measures trump commonly used objective measures: a systematic review.. British journal of sports medicine. doi:10.1136/bjsports-2015-094758 PMID 26423706
  9. Bosquet L, Merkari S, Arvisais D, Aubert AE (2008). Is heart rate a convenient tool to monitor over-reaching? A systematic review of the literature.. British journal of sports medicine. doi:10.1136/bjsm.2007.042200 PMID 18308872
  10. Bellenger CR, Fuller JT, Thomson RL, Davison K, Robertson EY, Buckley JD (2016). Monitoring Athletic Training Status Through Autonomic Heart Rate Regulation: A Systematic Review and Meta-Analysis.. Sports medicine (Auckland, N.Z.). doi:10.1007/s40279-016-0484-2 PMID 26888648
  11. Cadegiani FA, Kater CE (2017). Hormonal aspects of overtraining syndrome: a systematic review.. BMC sports science, medicine & rehabilitation. doi:10.1186/s13102-017-0079-8 PMID 28785411
  12. Greenham G, Buckley JD, Garrett J, Eston R, Norton K (2018). Biomarkers of Physiological Responses to Periods of Intensified, Non-Resistance-Based Exercise Training in Well-Trained Male Athletes: A Systematic Review and Meta-Analysis.. Sports medicine (Auckland, N.Z.). doi:10.1007/s40279-018-0969-2 PMID 30141022
  13. Meeusen R, Nederhof E, Buyse L, Roelands B, de Schutter G, Piacentini MF (2008). Diagnosing overtraining in athletes using the two-bout exercise protocol.. British journal of sports medicine. doi:10.1136/bjsm.2008.049981 PMID 18703548
  14. Buchwald RL, Buchwald J, Lehtonen E, Peltonen JE, Uusitalo ALT (2025). A Comprehensive Analysis of Overtraining Syndrome in Athletes and Recreational Exercisers.. International journal of sports medicine. doi:10.1055/a-2611-3598 PMID 40628368
  15. Kreher JB (2016). Diagnosis and prevention of overtraining syndrome: an opinion on education strategies.. Open access journal of sports medicine. doi:10.2147/OAJSM.S91657 PMID 27660501
  16. Matos NF, Winsley RJ, Williams CA (2011). Prevalence of nonfunctional overreaching/overtraining in young English athletes.. Medicine and science in sports and exercise. doi:10.1249/MSS.0b013e318207f87b PMID 21131861
  17. Kenttä G, Hassmén P, Raglin JS (2001). Training practices and overtraining syndrome in Swedish age-group athletes.. International journal of sports medicine. doi:10.1055/s-2001-16250 PMID 11531041
  18. Grandou C, Wallace L, Coutts AJ, Bell L, Impellizzeri FM (2021). Symptoms of Overtraining in Resistance Exercise: International Cross-Sectional Survey.. International journal of sports physiology and performance. doi:10.1123/ijspp.2019-0825 PMID 32679567
  19. Bell L, Ruddock A, Maden-Wilkinson T, Rogerson D (2020). Overreaching and overtraining in strength sports and resistance training: A scoping review.. Journal of sports sciences. doi:10.1080/02640414.2020.1763077 PMID 32602418
  20. Aubry A, Hausswirth C, Louis J, Coutts AJ, LE Meur Y (2014). Functional Overreaching. Medicine and science in sports and exercise. doi:10.1249/MSS.0000000000000301 PMID 25134000
  21. Hausswirth C, Louis J, Aubry A, Bonnet G, Duffield R, LE Meur Y (2014). Evidence of disturbed sleep and increased illness in overreached endurance athletes.. Medicine and science in sports and exercise. doi:10.1249/MSS.0000000000000177 PMID 24091995
  22. Murphy C, Svansdottir SA, Dupuy O, Louis J (2024). Does overreaching from endurance-based training impair sleep: A systematic review and meta-analysis.. PloS one. doi:10.1371/journal.pone.0303748 PMID 38809828
  23. Halson SL, Jeukendrup AE (2004). Does Overtraining Exist?. Sports medicine (Auckland, N.Z.). doi:10.2165/00007256-200434140-00003 PMID 15571428
  24. Budgett R (1998). Fatigue and underperformance in athletes: the overtraining syndrome.. British journal of sports medicine. doi:10.1136/bjsm.32.2.107 PMID 9631215
  25. Cadegiani FA, Silva PHL, Abrao TCP, Kater CE (2021). Novel Markers of Recovery From Overtraining Syndrome: The EROS-LONGITUDINAL Study.. International journal of sports physiology and performance. doi:10.1123/ijspp.2020-0248 PMID 33406484
  26. Kreher JB, Stepanek J, Amrine R, Reddy S (2025). Overtraining Syndrome (OTS) in Three Endurance Athletes and Roads to Recovery.. BMJ case reports. doi:10.1136/bcr-2025-265066 PMID 40623787
  27. Bellinger P (2020). Functional Overreaching in Endurance Athletes: A Necessity or Cause for Concern?. Sports medicine (Auckland, N.Z.). doi:10.1007/s40279-020-01269-w PMID 32064575
  28. Lewis NA, Collins D, Pedlar CR, Rogers JP (2015). Can clinicians and scientists explain and prevent unexplained underperformance syndrome in elite athletes: an interdisciplinary perspective and 2016 update.. BMJ open sport & exercise medicine. doi:10.1136/bmjsem-2015-000063 PMID 27900140
  29. Hoenig T, Ackerman KE, Beck BR, Bouxsein ML, Burr DB, Hollander K, Popp KL, Rolvien T, Tenforde AS, Warden SJ (2022). Bone stress injuries. Nature reviews. Disease primers. doi:10.1038/s41572-022-00352-y PMID 35484131
  30. Stellingwerff T, Heikura IA, Meeusen R, Bermon S, Seiler S, Mountjoy ML, Burke LM (2021). Overtraining Syndrome (OTS) and Relative Energy Deficiency in Sport (RED-S): Shared Pathways, Symptoms and Complexities.. Sports medicine (Auckland, N.Z.). doi:10.1007/s40279-021-01491-0 PMID 34181189
  31. Kuikman MA, Coates AM, Burr JF (2022). Markers of Low Energy Availability in Overreached Athletes: A Systematic Review and Meta-analysis.. Sports medicine (Auckland, N.Z.). doi:10.1007/s40279-022-01723-x PMID 35819582
  32. Cadegiani FA, Kater CE (2019). Novel causes and consequences of overtraining syndrome: the EROS-DISRUPTORS study.. BMC sports science, medicine & rehabilitation. doi:10.1186/s13102-019-0132-x PMID 31548891
  33. Mountjoy M, Ackerman KE, Bailey DM, Burke LM, Constantini N, Hackney AC, Heikura IA, Melin A, Pensgaard AM, Stellingwerff T, Sundgot-Borgen JK, Torstveit MK, Jacobsen AU, Verhagen E, Budgett R, Engebretsen L, Erdener U (2023). 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs).. British journal of sports medicine. doi:10.1136/bjsports-2023-106994 PMID 37752011

Every source the library cites

Changes

  • Revised to report sources added after their published corrections were read
  • First published.