Tachycardia in Athletes: Causes, Training Load and the Role of Drugs
A trained heart usually beats slowly at rest, so a racing pulse in an athlete is worth taking seriously. Sometimes the explanation is mundane, such as a hot day or a heavy week of training; sometimes it points to stimulant use, hormonal problems or a genuine rhythm disorder. Our editorial team explains how to tell the difference and when to seek help.
What counts as tachycardia
Tachycardia is conventionally defined as a resting heart rate above 100 beats per minute. During exercise, of course, rates well above this are normal and expected. What matters is the context: a fast rate at rest, a rate that is inappropriately high for the effort, or an abrupt jump that does not match what you are doing.
Endurance athletes commonly have resting rates in the 40s or 50s because training enlarges the heart's chambers and increases vagal tone. For such a person, a resting rate of 85 may already be a meaningful change even though it is technically "normal".
Doctors distinguish sinus tachycardia, where the heart's natural pacemaker simply fires faster, from arrhythmias such as supraventricular tachycardia (SVT), atrial fibrillation and, rarely, ventricular tachycardia. Sinus tachycardia is usually a response to something else; arrhythmias are electrical problems in their own right.
Wearable devices have made people far more aware of their heart rate. They are useful for spotting trends, but optical sensors can misread rhythm, so any persistent abnormality should be confirmed with an ECG.
Training-related causes
The most common reasons for a raised resting heart rate in athletes are linked to load and lifestyle rather than disease:
- Dehydration and heat: reduced blood volume means the heart beats faster to maintain output.
- Insufficient recovery: a morning pulse several beats above your usual baseline can signal accumulated fatigue.
- Illness: fever and viral infections raise heart rate; training through them carries a risk of myocarditis.
- Low energy availability: under-fuelling disturbs hormones and autonomic balance.
- Anaemia: low haemoglobin reduces oxygen-carrying capacity, especially in female and endurance athletes.
Overtraining syndrome, described in the joint European and American consensus by Meeusen and colleagues, can present with either increased or decreased resting heart rate, alongside persistent underperformance, mood changes and poor sleep. Heart rate alone is not diagnostic, but a sustained shift is a useful warning.
Long-term endurance training is also associated with a higher risk of atrial fibrillation in middle-aged men, as reported by Mont and colleagues. This is one of the few cardiac rhythm problems where the training itself appears to contribute.
Supplements, stimulants and performance drugs
Caffeine is the most widely used stimulant in sport. Moderate doses rarely cause problems in healthy people, but stacking coffee, energy drinks and high-dose pre-workout products can produce palpitations, anxiety and a racing pulse. Older pre-workouts containing DMAA or DMHA (now banned in many markets and prohibited in competition) have been linked with serious cardiovascular events.
Clenbuterol, a beta-2 agonist not licensed for human use in the UK and prohibited by WADA, reliably increases heart rate and has been associated with palpitations, arrhythmias and myocardial injury. Ephedrine and synephrine act in a similar direction. Thyroid hormones such as liothyronine (T3), misused for fat loss, can produce a hyperthyroid state with sustained tachycardia and atrial fibrillation.
Anabolic-androgenic steroids affect the heart more insidiously. The Endocrine Society statement by Pope and colleagues describes left ventricular hypertrophy, reduced heart function, adverse lipid changes and an increased risk of arrhythmias and sudden cardiac death associated with non-medical use. Growth hormone misuse can likewise lead to cardiac enlargement.
Beyond substances, recreational drugs such as cocaine and amphetamines, as well as withdrawal from alcohol, can all cause marked tachycardia. A frank conversation with a doctor about everything you take is essential for an accurate diagnosis.
| Substance group | Typical effect on heart rhythm | Notes |
|---|---|---|
| Caffeine, pre-workouts | Palpitations, sinus tachycardia | Dose-dependent; watch combined sources |
| Clenbuterol, ephedrine | Sustained tachycardia, arrhythmias | Prohibited in sport; serious risks |
| Thyroid hormones (T3/T4) misuse | Tachycardia, atrial fibrillation | Prescription-only medicines |
| Anabolic steroids, growth hormone | Structural heart changes, arrhythmia risk | Effects may persist after stopping |
| Cocaine, amphetamines | Severe tachycardia, ischaemia | Medical emergency risk |
Red flags and medical assessment
Seek urgent help by calling 999 if a fast heartbeat comes with chest pain, fainting, severe breathlessness or confusion. Collapse during exercise is always an emergency. For episodes that settle on their own, contact your GP or NHS 111 for advice.
Other warning signs include palpitations that start and stop abruptly, an irregular pulse, a heart rate that remains high long after exercise, and any family history of sudden cardiac death at a young age or of inherited heart conditions.
Assessment usually begins with a 12-lead ECG interpreted using athlete-specific criteria, such as the international recommendations published by Drezner and colleagues, which help avoid labelling normal training adaptations as disease. Further tests may include ambulatory ECG monitoring, an echocardiogram, an exercise test, and blood tests for thyroid function, haemoglobin and electrolytes.
The 2020 European Society of Cardiology guidelines on sports cardiology guide decisions about whether and how an athlete can continue competing. Many conditions, including most cases of SVT, can be treated effectively, often allowing a full return to sport.
Conclusions of the editorial team
For athletes, a raised resting heart rate is most often a sign of dehydration, illness or accumulated fatigue, and it settles with rest and fluids. Tracking your morning pulse is a simple, useful habit.
Persistent or unexplained tachycardia deserves an ECG, especially if you use stimulants, high-dose pre-workouts or any prescription-only performance drugs. Being open with clinicians about substance use leads to better, safer care.
Symptoms such as chest pain, fainting or abrupt-onset palpitations should never be trained through.
Readers may also be interested in our articles on the athlete's ECG, haematocrit monitoring and the cardiovascular effects of fat-burning drugs.
References
- Drezner JA, Sharma S, Baggish A, et al. International criteria for electrocardiographic interpretation in athletes: consensus statement. Br J Sports Med. 2017;51(9):704–731.
- Pelliccia A, Sharma S, Gati S, et al. 2020 ESC Guidelines on sports cardiology and exercise in patients with cardiovascular disease. Eur Heart J. 2021;42(1):17–96.
- Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia. Eur Heart J. 2020;41(5):655–720.
- Meeusen R, Duclos M, Foster C, et al. Prevention, diagnosis, and treatment of the overtraining syndrome: joint consensus statement of the European College of Sport Science and the American College of Sports Medicine. Med Sci Sports Exerc. 2013;45(1):186–205.
- Mont L, Elosua R, Brugada J. Endurance sport practice as a risk factor for atrial fibrillation and atrial flutter. Europace. 2009;11(1):11–17.
- Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
