Heart palpitations during exercise: harmless or a signal?

Heart palpitations during exercise are harmless in most cases. You are feeling your own heartbeat, and that sensation says nothing about your heart on its own. It becomes serious in combination: with fainting, with chest pain, or with breathlessness that does not match your effort.

That combination is the whole triage. The rest is noise.

Something I misread about myself for years: the fitter I got, the more often I felt my heart. It looked like decline. It was the opposite.

What are heart palpitations exactly?

Palpitations are the conscious awareness of your own heartbeat. Your heart pounds harder, runs faster, or seems to skip a beat. The word describes a sensation, not a diagnosis. In most people the underlying rhythm is entirely normal, it has simply become noticeable.

The medical term is palpitations.

That distinction matters more than it sounds. An arrhythmia can be measured on an ECG. Palpitations can only be felt. The two overlap only partly: many people with a measured arrhythmia feel nothing, and many people who feel something have a perfectly clean ECG.

Thuisarts, the Dutch GP guideline site, puts it plainly: in most people with palpitations, nothing serious is going on.

Why do you get palpitations during or after exercise?

During effort your adrenaline rises and your vagal brake drops away. Your heart beats harder and faster, and you feel it in your chest and throat. Afterwards that brake returns, sometimes with an overshoot. Athletes report the most unrest in exactly that transition.

The first half hour after a hard session is no coincidence.

Four routes come up most often in athletes. Exercise itself, with the adrenaline that goes with it. Recovery, with the rebound of your vagal system. Stimuli such as caffeine, alcohol, nicotine and lack of sleep. And fourth, a measurable cause in your blood, such as your thyroid or your iron stores.

That last category is rarely investigated first in the Netherlands.

Which is a pity, because it is the only category that leaves you with a number. How training drives your heart rate is covered in why your heart rate zones are probably wrong.

Why do trained athletes feel their heart more often?

Because training lowers your resting heart rate and raises your vagal tone. Against a slow, quiet rhythm an extra beat stands out far more than against a fast one. Your heart has not become more restless. Your background noise has gone quieter, so the outlier lands harder.

This is the point that appears on no Dutch page.

Smith and colleagues showed back in 1988 that endurance athletes have a more pronounced breathing-linked rhythm variation than untrained people, used as an index of cardiac vagal tone (PMID 3191665). That same variation is what your watch measures and calls HRV. A high HRV and the feeling of an irregular heart are therefore partly the same phenomenon.

What that variation actually is sits in HRV explained. Why a low resting heart rate is normal in athletes sits in resting heart rate and recovery.

Getting fitter can therefore increase your symptom without your heart getting worse. That is reassuring and confusing at the same time.

When should you see a doctor about palpitations?

For the accompanying symptoms, not for the pounding itself. Fainting or near-fainting during exertion is the most important one. After that come chest pain, breathlessness that does not match the effort, and a rhythm that starts suddenly, runs fast and stays irregular.

The Hartstichting and Thuisarts both draw that line.

The table below is meant to order your symptom, not to hand yourself a diagnosis.

One detail people often miss: an ECG at the GP while you feel nothing usually shows nothing. The rhythm has to be captured while you feel it. That is why a doctor often orders a Holter monitor or an event recorder.

What a clinical exercise test does and does not see sits in the exercise stress test explained.

Which blood values can explain palpitations?

Four groups. Your thyroid, your iron status, your electrolytes and your inflammatory markers. They do not explain every symptom, but they are the only causes you can rule out with a tube of blood. For a symptom lasting weeks, that is a reasonable first step.

This is the table missing from the rest of the search results.

The thyroid side is the best supported. Baumgartner and colleagues followed more than 30,000 people and saw that even thyroid values within the normal range tracked with the risk of atrial fibrillation, with a higher free T4 matching a higher risk (PMID 29061566).

Note what that says: within the normal range. A result does not have to be abnormal to mean something.

Imagine two runners of 34 reporting exactly the same symptom: a pounding heart at rest, mostly after dinner. One has a TSH of 0.3 with a high-normal free T4. The other has a tidy TSH of 1.8, but a ferritin of 12.

Same sensation, two different trails.

The first discusses her thyroid with her GP. The second looks at his iron intake and his training volume. Without those results both would have received the same advice: less coffee and more rest. For one of them that would have been the wrong advice.

The electrolyte side plays up mostly in summer and on long endurance sessions. What goes wrong then sits in electrolytes and hydration for athletes. For the thyroid, an underactive thyroid is the starting point.

These values sit together in the heart panel, so you see them side by side from one draw.

Does cutting caffeine help against palpitations?

Less than you would expect. The advice to drop coffee appears on almost every Dutch page about palpitations, but the evidence behind it is thin. In the one targeted study I could find, restricting caffeine in people with symptomatic extra beats produced no demonstrable benefit.

Newby and colleagues examined this in 1996 and concluded that caffeine restriction has no role in management (PMID 8983684).

That is an old study and a small group. So I do not present it as proof that caffeine does nothing. I present it as a reason to weigh your own experience more heavily than the standard advice.

Test it yourself, two weeks without, and see whether it makes a difference. Do not do that just before a race, because the withdrawal itself causes symptoms too. How caffeine works on performance otherwise sits in caffeine and pre-workout.

Among the athletes I speak to, sleep debt and alcohol are far more consistent triggers than coffee.

How often is a skipping heart too often?

Isolated extra beats are normal and happen to almost everyone. It only becomes concerning when they make up a large share of your total beats, and that can only be established with a 24-hour Holter. You cannot estimate that number by feel.

A figure exists for it.

Baman and colleagues found that a ventricular ectopic burden above 24 percent best separated people with impaired from normal pump function. The lowest burden that led to a reversible cardiomyopathy in their group was 10 percent (PMID 20348027).

Set that against your own experience. Ten percent of roughly 100,000 beats a day is 10,000 extra beats. Anyone feeling a few per hour sits far below that.

More on the isolated extra beat itself sits in premature heartbeats in athletes.

When does it point to atrial fibrillation?

When it is fast, stays irregular, and lasts minutes to hours rather than seconds. Atrial fibrillation is more common in endurance athletes than in age-matched people who do not train. It often feels like an engine running unevenly, with a clear loss of power during effort.

Duration is the most useful distinction.

A single extra beat lasts a fraction of a second. Atrial fibrillation persists, and many people mainly notice that their usual pace suddenly feels heavy. What that means for endurance athletes sits in atrial fibrillation symptoms in endurance athletes.

A regular rhythm that merely feels irregular and moves with your breathing is usually something else. That is described in sinus arrhythmia.

What does your smartwatch see, and what does it miss?

Your watch reads tempo and regularity reasonably well, but not the nature of the rhythm. A wrist sensor works optically: it measures colour change in your skin with each beat. That works well on a calm, regular rhythm and badly on the irregular rhythm that worries you.

That is an unfortunate combination.

Several watches also carry a single-lead ECG function, where you rest a finger on the crown or bezel. That is a different thing from the wrist reading and produces a real voltage signal. A hospital ECG uses twelve leads, so the comparison only goes so far.

In practice that gives you three usable things.

• The duration of an episode, because your watch logs time more accurately than your memory.
• Your heart rate at that moment, which pins down the difference between 95 and 160.
• A single trace you can show your doctor, provided you save it.

What it does not give you is a diagnosis. A possible atrial fibrillation alert is a reason to investigate, not a result. Equally, the absence of an alert rules nothing out, because your watch does not measure continuously and misses short episodes.

So treat your watch as a logbook, not a doctor. Why your heart rate zones are often set wrong besides sits in heart rate zones for training.

What can you do yourself about palpitations?

Measure instead of guess. Note when it happens, how long it lasts, and what came before it. Three weeks of such notes are more useful to a GP than a vague account, and they often reveal a pattern you had not seen yourself.

Put three things next to it: your sleep, your alcohol and your training load.

Use your watch for duration and regularity, not for diagnosis. A wrist sensor is an optical estimate and loses reliability precisely during an irregular rhythm. That is exactly the moment you would most want to trust it.

If the symptom persists after a month, blood testing is the first step with a concrete outcome. Your thyroid and your iron stores are the two that most often turn something up.

And the nuance that falls away most easily: your heart being more noticeable since you started training seriously is not a bad sign in itself. In my case it turned out to be a sleep question, not a heart question.

Every blood test result includes a professional assessment by a BIG-registered doctor. Discuss your results with your GP before making treatment decisions.

References

• Baman TS, Lange DC, Ilg KJ, et al. Relationship between burden of premature ventricular complexes and left ventricular function. Heart Rhythm, 2010;7(7):865-869. PMID 20348027.
• Baumgartner C, da Costa BR, Collet TH, et al. Thyroid function within the normal range, subclinical hypothyroidism, and the risk of atrial fibrillation. Circulation, 2017;136(22):2100-2116. PMID 29061566.
• Newby DE, Neilson JM, Jarvie DR, Boon NA. Caffeine restriction has no role in the management of patients with symptomatic idiopathic ventricular premature beats. Heart, 1996;76(4):355-357. PMID 8983684.
• Zhang D, Wang W, Li F. Association between resting heart rate and coronary artery disease, stroke, sudden death and noncardiovascular diseases: a meta-analysis. CMAJ, 2016;188(15):E384-E392. PMID 26598376.
• Smith ML, Hudson DL, Graitzer HM, Raven PB. Respiratory sinus arrhythmia and carotid baroreflex control of heart rate in endurance athletes and untrained controls. Clinical Physiology, 1988;8(5):511-519. PMID 3191665.
• Hartstichting. Heart rhythm disorders and exercise.
• Thuisarts. I have palpitations.