How to know if you are overtraining (and why you probably are not)

"Am I overtraining?" is one of the most searched questions in endurance sport, and almost everyone asking it is not. What most people have is functional overreaching, which is the thing training is supposed to do. Knowing which one you have determines whether you need a week or a season.

Three different things with three different answers

The ECSS and ACSM joint consensus statement separates them cleanly.

Functional overreaching is short-term performance decline from a deliberate hard block. You feel flat, you recover in days to a couple of weeks, and you come back fitter. This is the mechanism. It is not a problem.

Non-functional overreaching is the same decline without the rebound: stagnation or decline lasting weeks to months, usually with hormonal and psychological signs. You get back to where you were, but you paid weeks for nothing.

Overtraining syndrome is prolonged maladaptation across biological, neurochemical and hormonal systems, taking months to resolve and diagnosed largely by excluding everything else — anaemia, thyroid disease, infection, depression, under-eating. It is genuinely rare outside elite sport.

The consensus statement is blunt about the diagnostic problem: there is no single marker that identifies overtraining syndrome. Anyone selling you one is selling you something.

The signs actually worth watching

Because no single marker works, what matters is a cluster of them moving together, and moving away from your normal.

Performance that will not respond to rest. The definitional sign. If a genuine easy week does not bring you back, that is the one that counts.

Resting heart rate drifting up, HRV drifting down, both for weeks. Not one bad morning. A trend across two to three weeks, measured in the same conditions each day.

Effort that no longer matches pace. Your usual easy pace costing you zone three. This one is often the earliest.

Sleep getting worse while training gets harder. Counterintuitive and telling: fragmented sleep and early waking despite heavy fatigue.

Mood, motivation and appetite. The consensus statement takes these seriously, and so should you. Loss of drive to train is data.

Notice what is missing: being tired after a hard week, being sore, having one low HRV reading. Those are training.

The test that settles it

Take a real down week. Not a slightly easier week — cut volume by roughly half, remove all intensity, keep eating normally, and sleep as much as you can.

If you come back sharper within one to two weeks, you were functionally overreached and you have just completed the block correctly. If two weeks of genuine rest leaves you flat, stop guessing and see a doctor: the differential includes iron deficiency, thyroid dysfunction, undiagnosed infection, chronic under-fuelling and depression, all of which are more likely than overtraining syndrome and all of which are treatable.

What PeakU does with this

The reason this is hard to self-diagnose is that it requires holding weeks of several different signals in your head at once, from apps that do not talk to each other. PeakU tracks resting heart rate, HRV against your 30-day baseline, sleep, and acute-to-chronic load on one timeline, and the Peak Score is what those look like folded together.

It flags the pattern rather than the day: load climbing while HRV trends down and resting heart rate trends up, over weeks. The plan then proposes the down week before you have dug the hole, which is the only version of this that is actually useful — a warning after three bad months is a post-mortem.