The short version
- A review of elite young athletes put the incidence of overtraining syndrome at around 20 to 30%, with higher rates in individual sports, in females, and at the highest competitive levels.
- In a study of 39 athletes, 14 with overtraining syndrome and 25 healthy, training patterns were similar between the groups, so excessive training was not a risk factor or predictor in that cohort.
- In the same study, daily carbohydrate, daily protein and daily overall calorie intake were the independent triggers of overtraining syndrome.
- Reviews report the association between training load and overtraining to be unclear, which is why non-training stressors are weighed alongside training ones.
- The IOC's 2023 consensus defines Relative Energy Deficiency in Sport as a syndrome of health and performance problems caused by energy intake that is inadequate relative to exercise energy expenditure.
The name is the problem. "Overtraining syndrome" tells you the cause before anyone has looked, and the research on people who genuinely have it keeps failing to find that cause where the name says it should be.
How common is it, and what does it look like
Winsley and Matos reviewed the evidence in elite young athletes and put the incidence rate at around 20 to 30%, with a higher occurrence in individual sport athletes, in females, and in those competing at the highest representative levels.
The symptom list they report is worth reading in full, because it is broader than "tired and weak": an increased perception of effort during exercise, frequent upper respiratory tract infections, muscle soreness, sleep disturbances, loss of appetite, mood disturbances, shortness of temper, decreased interest in training and competition, decreased self-confidence, and an inability to concentrate.
Two of those get missed constantly. Increased perception of effort — the same session feels harder at the same output — is often the earliest sign. And repeated minor illnesses are treated as bad luck rather than as data.
Then their finding that ought to be more famous: the association between training load and overtraining is unclear, which is why they argue for a holistic approach that weighs non-training stressors as seriously as training ones.
The study that put a number on that
Cadegiani and Kater analysed the full dataset of the EROS study — 39 athletes, 14 with overtraining syndrome and 25 healthy, across 117 markers — testing modifiable factors as independent predictors.
Training patterns were similar between the affected and healthy athletes. Excessive training was therefore not a risk factor in this cohort, and consequently not a predictor. What independently triggered the syndrome were three dietary variables: daily carbohydrate intake, daily protein intake and daily overall calorie intake. Sleep and social characteristics only contributed in combination with other factors.
Once triggered, the syndrome independently reduced cortisol and late growth hormone and ACTH responses to stimulation, the testosterone-to-oestradiol ratio, neutrophils, vigour, hydration status and muscle mass, while increasing tension levels and visceral fat.
Now the caveats, which are substantial. Thirty-nine athletes is small. It is one research group, one cohort, and the design identifies predictors rather than proving causation. This is a hypothesis with good measurements behind it, not a settled fact — and we would rather hand it to you that way than as a headline.
The same idea has a bigger, better-supported name
What EROS describes is close to something sports medicine has been building a consensus around from a different direction. The International Olympic Committee's 2023 consensus statement on Relative Energy Deficiency in Sport defines a syndrome of deleterious health and performance outcomes in female and male athletes exposed to low energy availability — inadequate energy intake relative to exercise energy expenditure. The statement notes more than 170 original research publications since the previous consensus, emerging evidence on the role of low carbohydrate availability specifically, and the interplay between mental health and the condition.
Two independent lines of work, arriving at eating rather than training as the lever. That convergence is worth more than either on its own.
Overreaching, and the thing it is not
Feeling flat for a fortnight is normal and usually functional — the dip resolves into improvement once load comes down, which is training working as designed. The distinction that matters practically is not a lab test. It is what happens next. A lighter week that restores you means you were overreached. A lighter week that changes nothing means the question has moved.
What we'd actually tell you
Take the deload first, because it is free and it is diagnostic. While you do, count your food honestly for a week — not to diet, but to find out whether your intake matches what you are asking your body to do. On the evidence above, that is where the difference showed up.
Protect sleep, because it is the input with the largest measured cost when it is missing, and the relationship between sleep and muscle recovery is better established than anything in the recovery aisle. Do not spend money on a resting heart rate variability subscription hoping it will diagnose this; resting HRV is largely unaffected by overreaching, so a normal score is not reassurance.
And go to a clinician sooner than feels justified. Persistent underperformance overlaps almost perfectly with iron deficiency, thyroid disease, coeliac disease, sleep apnoea, glandular fever and depression, and every one of those is more common and more treatable than true overtraining. Underperformance plus unintended weight loss, a lost menstrual cycle, repeated infections or persistent low mood is a medical appointment, not a programming tweak. No supplement treats this, ours included, and any product marketed as doing so is selling to a person who should be in a consulting room.
Good questions
What are the first signs of overtraining?
An increased perception of effort at the same workload is often earliest — the session feels harder without being harder. Reviews also list frequent upper respiratory infections, sleep disturbance, loss of appetite, irritability, decreased interest in training, lower self-confidence and poor concentration. Most people notice the mood and illness signs long before they connect them to training, which is why they get attributed to a stressful month instead.
Can you get overtraining syndrome from eating too little?
That appears to be a major route. In one study of 39 athletes, training patterns were the same in affected and healthy groups, while carbohydrate, protein and total calorie intake independently predicted who had the syndrome. The IOC's consensus on Relative Energy Deficiency in Sport describes the same territory from a different direction. Underfuelling a heavy training load is a genuinely plausible cause.
How long does it take to recover from overtraining?
Nobody can give you a reliable figure, and that uncertainty is itself informative. Short-term overreaching typically resolves within days to a couple of weeks of reduced load. Genuine overtraining syndrome is described as prolonged, and is diagnosed largely by exclusion and by what fails to resolve. If a lighter week changes nothing, stop guessing at timelines and get medical input.
Is overtraining just an excuse for being unfit or lazy?
No, and that framing does real damage. It has a measurable physiology — in one study it independently reduced hormonal responses to stimulation, neutrophils, vigour, hydration and muscle mass while raising tension and visceral fat. It also occurs at incidence rates around 20 to 30% in elite young athletes. Pushing through it is the behaviour that turns a recoverable dip into a long one.
Do I need a blood test to diagnose overtraining?
Not to diagnose it, but you probably need one anyway. There is no confirmatory test for overtraining syndrome; it is largely a diagnosis of exclusion. What blood work does well is rule out iron deficiency, thyroid disease, coeliac disease and infection, which mimic it closely and are far more common and more treatable. Ask a clinician to exclude the ordinary causes before accepting the exotic one.
Can supplements help with overtraining?
No, and we would rather lose the sale than pretend otherwise. The evidence points at energy intake, training load and sleep as the levers, and no capsule alters any of those. A supplement can support ordinary nutritional gaps during a hard block. If a product is marketed as treating or preventing overtraining, it is being sold to somebody who should be talking to a clinician instead.
Sources
- Winsley R, Matos N. Overtraining and elite young athletes. Med Sport Sci, 2011. View study
- Cadegiani FA, Kater CE. Novel causes and consequences of overtraining syndrome: the EROS-DISRUPTORS study. BMC Sports Sci Med Rehabil, 2019. View study
- Mountjoy M, Ackerman KE, Bailey DM, Burke LM, Constantini N, Hackney AC, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med, 2023. View study
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