Recognizing overtraining: the quiet warning signs your body sends you

You notice it first on a Tuesday morning

The alarm goes off. You are not tired in the sense of sleepy. You are heavy. You spent eight hours in bed and feel as if you had five.

You go running anyway. The first few kilometers feel sluggish, you know that feeling. But they do not get better. At the same pace, your heart rate sits ten beats higher than it did three weeks ago. You explain it with the weather. With stress at work. With the wine on Saturday.

In the evening you are awake. Not energized, more like wired. The body is empty, the head keeps running. And somewhere in that week comes the third cold since October.

In my practice I often turn that question around. Not: what is wrong with your willpower? But: what is your nervous system doing right now? What is your stress axis doing? How much energy is actually available to your body after training has taken its share?

Three stages that often get lumped together

Before we talk about symptoms, we need terms. In everyday language, everything is called overtraining. In sports medicine there are three distinct states with very different outlooks.

The joint consensus statement of the European College of Sport Science and the American College of Sports Medicine set out this classification in 2013. It still serves as the reference today.

A working group at the University of Basel followed up in 2022 and looked systematically at what had been added since. They screened 5,561 hits and kept 39 studies that held up to the criteria. What they found were three diagnostic scores from the Brazilian EROS investigation plus a long list of possible building blocks: basal hormones, hormonal responses to stimuli, psychological questionnaires, exercise tests, heart rate variability, EEG, immunological parameters and body composition.

Their conclusion is the core of this article: overtraining syndrome is a state of several systems at once. Only the combination of variables produces a picture you can work with.

And now you know why a normal blood count at your family doctor is no contradiction of what you are experiencing. The blood count answers a different question than the one about a pattern across several weeks. Only together do they make a picture.

The seven quiet warning signs

The first thing most people expect is a drop in performance. That does come. It just often comes last. Before that, the body speaks through channels that no training app tracks.

The same study delivered a second number that I mention in almost every consultation. The frequency of respiratory tract infections was 67 percent in the overloaded group. Among the athletes who handled the same load well, it was 22 percent. In the control group, 11 percent.

What happens in the nervous system: resting heart rate and HRV

Your heart never beats entirely evenly. Between two beats there are sometimes 820 milliseconds, sometimes 861. This variation is called heart rate variability, HRV for short. It is not an error, it is a feature.

Imagine your autonomic nervous system as a car with two pedals. The sympathetic system is the accelerator, the parasympathetic system is the brake. A healthy system switches smoothly between the two. HRV measures that flexibility.

A study of 15 athletes with three weeks of overload of plus 45 percent and a subsequent reduction of 20 percent showed another interesting observation. Eight athletes responded to the same load with a loss of performance, seven with a gain. Baroreceptor sensitivity rose during the recovery phase only in the positive responders. The quickest distinguishing features during the overload phase, however, were not the lab values but submaximal performance and the subjective sense of exhaustion.

What happens in the hormonal system: the response gets quieter

Cortisol has a bad reputation. Unfairly so. Cortisol is not your enemy, it is your mobilizer. It pulls energy out of storage when you need it, and it makes sure you get out of bed in the morning.

What is interesting in overtraining is rarely the absolute level of a hormone value. What is interesting is how strongly your system can still respond when it is challenged.

A Belgian working group took this idea further in diagnostic terms. Using a database of 100 athletes, they tested how well non-functional overreaching can be distinguished from overtraining syndrome. The most informative were the ACTH and prolactin responses to a second exercise test on the same day. For prolactin, sensitivity was 93 percent in the case of overtraining syndrome, for ACTH 67 percent.

When hormones and psychological changes were evaluated together, sensitivity rose to 98 percent. The three most important variables were the ACTH and prolactin responses along with the sense of exhaustion. Important here: that is a research protocol with two exercise tests on the same day and serial hormone sampling. It is not available in routine care, and only sensitivity was reported, not specificity. That level of accuracy therefore does not carry over into everyday practice.

And that closes a circle that was long underestimated in sports medicine. A systematic review by Saw, Main and Gastin analyzed 56 studies in which subjective and objective measures were collected at the same time. The two groups mostly did not correlate. And the subjective reports reflected acute as well as chronic training load more sensitively and more consistently than the objective markers.

Immune system: why you keep getting sick

The mucous membranes in your mouth and nose are your first line of defense. That is where an antibody called secretory immunoglobulin A, sIgA for short, sits. Picture a doorkeeper who decides who gets in.

If the load stays high and recovery is missing, this doorkeeper can get tired. She is still there, but she checks less carefully.

There is also the opposite perspective, and it belongs here. A Swedish analysis of 61 training years in 11 elite endurance athletes found a clearly negative relationship between training hours per year and days lost to illness. Those who trained a lot were rarely ill. The authors argue that high training volumes and high infection rates simply do not go together.

Metabolism: too little energy is often the real trigger

This is the part I most often see overlooked in practice. It is not the excess of training that creates the problems. It is the shortfall of energy sitting next to it.

The International Olympic Committee updated its consensus statement on Relative Energy Deficiency in Sport in 2023. The term describes a state in which the available energy is too low relative to training expenditure. According to the author group, more than 170 new original papers have been added since the 2018 version, among them considerably more data on men and on the role of carbohydrate availability.

The consequences do not concern performance alone. The paper describes effects on the hormonal system, bone, immune function and mental health. For diagnostics, a dedicated tool was developed that works with a four-step traffic light, from green through yellow and orange to red, each with recommendations on training and competition participation.

This perspective is also the reason why, with athletes who are exhausted, I always ask about life outside training. A marathon build-up alongside a house move, a separation and night shifts is something different from the same build-up in a quiet phase of life. Much suggests that the body does not cleanly separate training stress from life stress, but that both act on the same control loops.

Ferritin, thyroid and the things that belong on the table first

Overtraining syndrome is a diagnosis of exclusion. In concrete terms that means: before anyone gets this label, other causes of the same symptoms have to be off the table.

The ECSS/ACSM consensus explicitly names organic disease, infections, caloric restriction, insufficient carbohydrate or protein intake, iron deficiency, magnesium deficiency and allergies.

In practice further causes come on top that can produce the same exhaustion, and I ask about them actively. A past infectious mononucleosis with EBV, where a break from contact sport can be necessary because of the enlarged spleen. Coeliac disease or another form of malabsorption. An unnoticed blood loss from the gastrointestinal tract as the reason for the empty iron store, particularly when the store does not rise despite supplementation. Sleep apnoea, especially with snoring and daytime sleepiness. And diabetes or impaired glucose tolerance. That is not a complete list, but it shows how much belongs on the table before the label overtraining.

One pitfall belongs with this: ferritin rises with inflammation and after infections. A value that looks normal can therefore mask an empty store. This is why an inflammatory marker such as CRP belongs alongside it and has to be read together with it.

From my perspective in practice, a sensible first work-up for athletes with persistent exhaustion covers at least these areas. What is actually needed in an individual case is decided in the consultation, not at a desk.

Three levers for the next seven days

You do not need a lab to get started. You need a week and a bit of consistency.

These six questions are not a validated test, they are a way into a conversation. If you get stuck on several of them, that is no reason to panic. It is a reason to plan the next training week deliberately differently and to have a doctor check whether something else is behind it, instead of carrying it alone.

Where the science ends today

I think it is important to draw a line here rather than claim a certainty that does not exist.

Well supported: there is a continuum from functional overreaching through non-functional overreaching to overtraining syndrome. Changes in sleep, increased infection rates and changes in mood occur more frequently in overloaded athletes. Subjective self-report is a sensitive indicator. Low energy availability has systemic consequences.

Mechanistically plausible, but not yet conclusively clarified: the precise role of individual hormonal axes and the question of whether the observed changes are cause or consequence. The role of oxidative stress has been described, but the data base is small. A Georgian study of 43 affected and 40 healthy athletes found elevated reactive oxygen metabolites and a lower antioxidant capacity, which partly receded after rest periods. That is an interesting signal, but not a solid basis for decisions in individual cases.

A limitation that applies to almost all the papers cited here: the athletes studied were predominantly male. Le Meur, Hausswirth, Woods and Tiernan included men only. For female athletes the markers and cut-offs have barely been validated so far, and the menstrual cycle changes resting heart rate and HRV on top of that. What is written here therefore does not transfer one to one. The Japanese ferritin study is the only one of the load-bearing papers that includes female athletes in a relevant number.

Still open: whether there is a marker or a validated combination that can be used across the board. The EROS scores are promising, but the authors of the Basel review point out that they still need to be validated in larger samples and particularly in female athletes. For strength sports, according to the scoping review with 47 included papers, the evidence is considerably thinner than for endurance sports.

An American review now suggests treating overtraining syndrome fundamentally as a complex system rather than as a linear chain of cause and effect. The authors argue that the classic method of breaking a problem down into individual variables reaches its limits here. That matches what I see clinically: people rarely come with one problem, they come with a pattern.

If the topic interests you further

These articles pick up individual threads that were only touched on here.

Frequently asked questions about overtraining