Marathon running

Is running a marathon safe?

For almost everyone who trains for it, yes. The main serious risk is sudden cardiac arrest, and it is rare. The largest study, by Jonathan Kim and colleagues in JAMA in 2025, followed 29.3 million finishers of US half and full marathons from 2010 to 2023. There were 176 cardiac arrests. In marathons, the rate was 1.04 per 100,000 runners, about twice that in half marathons.

The bigger news is survival. In 2000–2009, 71% of runners who arrested died. In 2010–2023 it was 34%. Cardiac deaths across all these races fell from 0.39 to 0.20 per 100,000 finishers. Combining the marathon arrest rate with today's fatality rate gives our estimate of about 3.5 micromortsMicromortA one-in-a-million chance of death. It lets you compare the risk of very different activities on one scale.More in the glossary per marathon.

What happens in a race cardiac arrest

The arrests that kill runners are mostly not freak events in young athletes. Among the 67 cases where the cause was found, coronary artery disease was the most common, ahead of hypertrophic cardiomyopathy, the inherited heart muscle condition often linked to young athletes' deaths. Men had 1.12 arrests per 100,000 finishers, women 0.19.

That points to a familiar profile: a middle-aged man, often fit and experienced, with narrowed coronary arteries he did not know about. Race-day effort, heat and adrenaline can trigger the arrhythmia that a less demanding day would not.

Why fewer runners now die

The JAMA authors credit "effective emergency action planning with immediate access to defibrillation". Runners who survived got CPR sooner and were more often in a shockable heart rhythm. Big races now place medical teams and automated external defibrillators (AEDs) along the course, so a collapsed runner can be reached and shocked within minutes.

The comparison with a cardiac arrest in the street is striking. Outside hospital, most people who arrest do not survive. On a well-run marathon course, about two in three now do.

Other race-day risks

Cardiac arrest is not the only reason runners end up in a medical tent, though it is the main cause of death:

• Heat stroke. Hot and humid race days raise the core temperature of runners pushing hard, and confusion or collapse late in the race is the warning. It is treated with rapid cooling on site.
• Low blood sodium (hyponatraemia). Drinking far more than you sweat, often by slower runners who stop at every water station, can dilute blood sodium dangerously.
• Falls and collapse at the finish. Most finish-line collapses are from blood pressure dropping when runners stop, and recover quickly when lying down with the legs raised.

Most medical tent visits are for cramps, blisters and exhaustion.

Who should be careful

• Men over about 40, and anyone with heart disease, high blood pressure, diabetes, high cholesterol, a smoking history or a family history of early heart disease. Talk to your doctor before starting a training plan.
• Anyone with warning signs in training: chest pain or pressure, unusual breathlessness, palpitations or fainting during exercise. Stop and get checked; do not run through it.
• Runners on a hot day. Slow down well below goal pace when temperatures are high. Some races issue heat warnings and let runners defer to another year.

How to run a marathon more safely

1. Train for it. Build up over months, not weeks. Long runs at an easy pace prepare the heart and legs.
2. Do not run when ill, especially with a fever or a recent viral infection.
3. Drink to thirst, not on a schedule, and do not gain weight during the race.
4. Adjust for heat. Slow down, pour water over yourself and walk if you feel dizzy or confused.
5. Know where the medical points and AEDs are. If a runner collapses near you, call for help, start chest compressions and send someone for the nearest AED.
6. Learn CPR. It is the single thing that most improves the odds for a runner who arrests.

How we scored it

Fatality risk (76) reflects about 3.5 micromortsMicromortA one-in-a-million chance of death. It lets you compare the risk of very different activities on one scale.More in the glossary per marathon. Injury risk (85) is low on race day, and the rescue environment (92) is among the best on our list because of on-course medical cover. Controllability (70) loses points for hidden heart disease. Compare cycling, the other endurance activity we score, and scuba diving, where heart events also drive many deaths.