Overtraining syndrome: why the lab results are almost always “normal”

A scenario familiar to almost anyone who has ever seriously ramped up their volume: your pace at your usual heart rate has dropped off, your legs have felt heavy for three weeks straight, your sleep has gone bad, and motivation is gone. The logical first step is to get bloodwork done. And this is where the real disappointment sets in: more often than not, everything comes back normal. That does not mean you imagined it. It means overtraining simply cannot be caught this way.

It is a spectrum, not a switch

The confusion starts with the terminology, so let us clear that up first. The consensus definition (the joint ECSS and ACSM statement, 2013) describes three states that differ not so much in symptoms as in how long it takes to get back to normal:

Functional overreaching — a planned dip in form after a hard block. Recovery takes days, and supercompensation follows. This is a normal and necessary part of training.
Non-functional overreaching — the same drop, but climbing out of it stretches over weeks or months, with no gain at the end.
Overtraining syndrome (OTS) — a severe state, with recovery measured in months and years.

The problem is that in the moment all three look the same. You can only tell them apart in hindsight, by how long it took you. That is exactly why declaring “I'm overtrained” four days after a hard week is almost certainly the wrong diagnosis.

Why lab tests do not help

A recent scoping review (Carrard et al.) pulled together 39 publications covering 30 independent studies, with 952 people in total — 328 with signs of OTS and 624 as controls. The goal was simple: find a test that establishes the diagnosis. The conclusion is discouraging: there is no gold standard, and OTS remains a diagnosis of exclusion.

Some patterns do show up in the data. People with OTS were found to have reduced testosterone, elevated cortisol and a blunted response to stimulation tests; shifts in glutamine and the lipid profile; changes in immune markers and oxidative stress; a shift in heart rate variability toward parasympathetic dominance; and a characteristic psychological profile on the POMS questionnaire — high fatigue and low vigour. The EROS scales (clinical, simplified and full) deserve a separate mention: in these studies they managed to separate every presumably overtrained male athlete from healthy ones.

But then come the caveats. No single marker has sufficient discriminative power — the authors state outright that combinations of variables are required, because the condition affects multiple systems. And the EROS scales still need to be validated in large samples and in women, who were almost absent from the research.

Hence the practical takeaway: normal bloodwork does not rule out overtraining, and “bad” cortisol on its own does not confirm it.

What to actually track

Since there are no laboratory answers, the things that work are simple ones you can keep track of yourself. The key idea is to compare yourself with yourself doing identical work:

Heart rate at a fixed pace. Not maximum, but specifically submaximal: the same speed on the same loop. A rising heart rate at an unchanged pace — or, conversely, a heart rate that “refuses to climb” even though the effort feels hard — is a signal.
Heart rate recovery speed after a standard interval.
Perceived exertion (RPE) on familiar work. If your usual easy run consistently feels a point or two harder, that is data, not whining.
Mood and vigour. It is no accident that POMS-style scales turned out to be among the most sensitive markers: the psychological profile often changes before the physiological one.
Power or pace on a benchmark segment — a drop that does not come back after a week of unloading.

None of these indicators is a diagnosis. But their combined trend is more informative than any single test tube.

When to see a doctor

Here is an important turn: before you diagnose yourself with overtraining, you need to rule out the things that are treatable. The consensus approach requires first eliminating other causes — and the list is quite specific: iron deficiency and anaemia, thyroid disorders, depression, plus infections and energy deficiency.

This is not a formality. The symptoms of all of these conditions overlap almost completely: fatigue, declining performance, poor sleep, apathy. The difference is that iron and the thyroid can be corrected, whereas “overtraining” is only cured by time.

So the correct order is this: a prolonged drop in form → a basic medical work-up (including ferritin and thyroid hormones) → and only with clean results a conversation about overreaching. Energy deficiency deserves separate attention: underfuelling on top of high volume produces a very similar picture.

And finally, the only thing that genuinely works once the condition has developed is reducing the load and giving it time. Trying to “run through it” stretches the road from weeks into months.

Key points

Overtraining is a spectrum: functional overreaching (days), non-functional (weeks to months), OTS (months to years). In the moment they are indistinguishable.
There is no gold standard for diagnosis; OTS is a diagnosis of exclusion. A review of 30 studies and 952 people confirmed this.
Individual biomarkers lack sufficient discriminative power — combinations are needed; the EROS scales are promising but untested in women.
Track submaximal heart rate, heart rate recovery, RPE on familiar work, mood and a benchmark segment — the trend, not one-off values.
First rule out iron, thyroid, depression and energy deficiency — unlike overtraining, these are treatable.
The only therapy that works is unloading and time. You cannot “run through” this condition.

Sources: Carrard J., Rigort A.-C., Appenzeller-Herzog C. et al. “Diagnosing Overtraining Syndrome: A Scoping Review”, Sports Health, 2022. https://doi.org/10.1177/19417381211044739. Joint ECSS and ACSM statement on overreaching and overtraining syndrome, 2013. “Diagnosis and Prevention of Overtraining Syndrome: an opinion on education strategies”, Open Access Journal of Sports Medicine. https://www.dovepress.com/diagnosis-and-prevention-of-overtraining-syndrome--an-opinion-on-educa-peer-reviewed-fulltext-article-OAJSM