Overtraining in athletes: causes and the link with load and pharmacology
Overtraining syndrome is one of the most misunderstood problems in sport. It is not simply the fatigue of a hard week, but a prolonged state of underperformance that can take months to resolve. This editorial overview examines what causes it, how training load and recovery interact, and why stimulants and hormones can dangerously mask the warning signs.
From overreaching to overtraining
Training works by stress and adaptation: a hard session damages and fatigues the body, and rest allows it to rebuild stronger. Sports scientists describe a continuum. Short-term overload followed by recovery produces "functional overreaching", which improves performance. Pushing further without adequate recovery produces "non-functional overreaching", where performance stalls for weeks.
At the far end lies overtraining syndrome itself, a state of persistent underperformance, fatigue and disturbance of mood and physiology that can last for months. The distinction matters because the early stages are a normal, planned part of training, whereas overtraining syndrome is a maladaptive failure of the balance between stress and recovery.
Crucially, overtraining syndrome is a diagnosis of exclusion. Before attributing an athlete's decline to it, clinicians rule out other causes: iron deficiency, thyroid problems, infection (including glandular fever), depression, poor nutrition and inadequate energy availability. Many cases labelled "overtraining" turn out to be one of these treatable conditions.
This framing is essential because it reframes overtraining not as a badge of hard work but as a signal that the system has been pushed beyond its capacity to adapt. Recognising the continuum early is the key to avoiding the severe end.
The central role of load and recovery
At its heart, overtraining is an imbalance: training load, including its volume, intensity and frequency, exceeds the body's capacity to recover. Recovery is not merely rest between sessions; it includes sleep, nutrition, energy availability and psychological stress from life outside sport. A sudden spike in load, or chronic under-recovery, tips the balance.
Research on training-load monitoring, including the work on acute-to-chronic workload ratios, highlights that rapid increases in load relative to what an athlete is accustomed to are associated with greater injury and breakdown risk. The body adapts to gradual, progressive increases far better than to abrupt jumps.
Energy availability is a particularly important and often overlooked factor. When athletes do not eat enough to fuel their training — whether deliberately or inadvertently — the body enters a state of low energy availability that impairs recovery, hormones, bone health and immunity. This overlaps with, and can masquerade as, overtraining.
Psychological load counts too. Exams, work stress, relationship difficulties and poor sleep all draw on the same recovery reserves as training. An athlete under heavy life stress needs more recovery, not less, yet this is frequently ignored in training plans that account only for physical load.
How the body signals trouble
Overtraining produces a cluster of signs across several systems. Performance plateaus or declines despite continued or increased effort. Perceived effort rises for the same workload. Athletes often report persistent fatigue, disturbed sleep, loss of appetite, irritability and low mood. These psychological changes are among the most consistent markers.
Physiological signals are less reliable than once thought. Resting heart rate and heart-rate variability can change, but not consistently enough to serve as a standalone test. Hormonal disturbances, altered immune function and raised susceptibility to minor infections are described, but no single blood test confirms the diagnosis.
| Domain | Warning signs |
|---|---|
| Performance | Unexplained plateau or decline; higher perceived effort |
| Mood | Irritability, low mood, loss of motivation |
| Sleep | Difficulty sleeping despite fatigue |
| Recovery | Prolonged soreness, slow recovery between sessions |
| Health | Frequent minor infections, appetite loss |
Because the signs are non-specific, monitoring tools such as training diaries, mood questionnaires and simple performance tests are more useful collectively than any single measure. The most practical early warning is often subjective: an athlete who feels persistently flat, unmotivated and heavy-legged despite rest deserves attention.
The key clinical principle remains exclusion. An athlete presenting with these features should be assessed for anaemia, thyroid dysfunction, infection, depression and nutritional deficiency before the fatigue is attributed to training alone.
How pharmacology masks the warning signs
This is where pharmacology enters the picture, and where real danger lies. Stimulants such as caffeine in high doses, ephedrine-type compounds and other "pre-workout" stimulants can temporarily override the sensation of fatigue. By masking the body's warning signals, they allow an athlete to keep pushing past the point where they should have rested, deepening the underlying problem.
This masking effect is treacherous precisely because it feels like a solution. The stimulant restores a feeling of energy, so the athlete trains harder, but the underlying deficit in recovery is not addressed and may worsen. The crash, when it comes, can be more severe for having been postponed.
Anabolic and hormonal agents complicate the picture differently. By promoting recovery and tissue repair, they can allow higher training loads to be tolerated for a time, which some interpret as evidence that more load is harmless. But such agents carry their own substantial health risks, do not eliminate the need for genuine recovery, and can disguise the accumulating strain on the body until a problem surfaces elsewhere — in the heart, the hormonal system or mental health.
- Stimulants suppress the perception of fatigue without fixing the deficit.
- High-dose caffeine can disturb the very sleep that recovery depends on.
- Hormonal agents may mask strain while adding their own serious risks.
- Painkillers taken routinely can hide injury that needs rest.
The honest message is that no pharmacological agent is a substitute for recovery. Masking fatigue is not the same as resolving it, and the practice of chemically pushing through warning signs is a recognised route into deeper overtraining and injury.
Prevention and recovery
Prevention rests on managing load intelligently and respecting recovery. This means progressing training gradually, building in planned rest and lighter "deload" periods, and monitoring how an athlete is responding rather than blindly following a fixed plan. Periodisation — structuring training into cycles with varying load — is the evidence-informed way to balance stress and adaptation.
Fuelling adequately is non-negotiable. Ensuring sufficient energy, carbohydrate and protein to match training demands protects against the low-energy-availability state that underlies much of what is loosely called overtraining. Adequate sleep, ideally prioritised as seriously as training itself, is among the most powerful recovery tools available.
When overtraining syndrome is established, the only reliable treatment is prolonged rest and a graded, patient return. This can take weeks to months, which is frustrating for competitive athletes but necessary. Attempting to train through it, or to mask it with stimulants, prolongs the problem.
Finally, an athlete experiencing persistent fatigue and decline should seek medical assessment rather than self-managing. A clinician can exclude treatable causes and guide a safe return. The temptation to reach for a chemical fix should be resisted; it addresses the symptom while leaving the cause untouched.
Conclusions of the editorial team
Overtraining is fundamentally a failure of the balance between load and recovery, sitting at the far end of a continuum that begins with normal, planned overreaching. Its signs are non-specific, which is why it remains a diagnosis of exclusion and why treatable conditions must be ruled out first.
The pharmacological angle is the most dangerous: stimulants and hormonal agents can mask the warning signs, letting an athlete push past the point of sensible rest and deepening the underlying deficit while adding their own risks. No substance replaces genuine recovery.
Our related material on energy availability in sport, on sleep and recovery, and on the honest risks of stimulant "pre-workouts" develops these themes further.
References
- Meeusen R, Duclos M, Foster C, et al. Prevention, diagnosis and treatment of the overtraining syndrome: joint consensus statement of the ECSS and ACSM. Med Sci Sports Exerc. 2013;45(1):186–205.
- Kreher JB, Schwartz JB. Overtraining syndrome: a practical guide. Sports Health. 2012;4(2):128–138.
- Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016;50(5):273–280.
- Mountjoy M, Sundgot-Borgen J, Burke L, et al. IOC consensus statement on relative energy deficiency in sport (RED-S). Br J Sports Med. 2018;52(11):687–697.
- Halson SL. Monitoring training load to understand fatigue in athletes. Sports Med. 2014;44(Suppl 2):S139–S147.
