Endurance Exercise and the Heart: New Review Covers 3 Types of Changes in Extreme Athletes
Endurance exercise protects the heart, but at extreme volumes it may move from healthy adaptation to changes that are not. That is the argument of a review published on 20 October in Cardiology in Review by two researchers from Udayana University in Bali, Indonesia, which covers the structural, functional and electrical changes described in ultra-endurance athletes.
What the review says about endurance exercise
The authors are Juven Luvianto and Luh Oliva Saraswati Suastika, from the cardiology department at Udayana University. The full text is paywalled; the abstract is on PubMed and on the journal website.
Their starting point is that the cardiovascular benefits of exercise may not keep growing with volume and intensity. With more people entering ultramarathons and long events, they review what is known about very high doses of endurance exercise. According to the abstract, the evidence points to three groups of changes:
- Extreme exertion can cause temporary cardiac dysfunction. Repeated over years, it may contribute to myocardial fibrosis, meaning scar tissue in the heart muscle, and to related arrhythmias.
- Endurance athletes often show more coronary artery calcification, more atherosclerotic plaque and stiffer arteries.
- Long-term endurance exercise is linked to a higher incidence of atrial fibrillation, the most frequent sustained arrhythmia.
In their conclusion, the authors write that regular exercise is unequivocally cardioprotective, that the long-term effects of extreme training are still debated, and that assuming more exercise is always better no longer seems prudent.
A narrative review with no new data
This is a narrative review: the authors summarise existing literature, but they do not run a meta-analysis or report their own patients, and the abstract gives no figures. To see how large the effects are, you have to go to the original studies. Two earlier studies put numbers on some of its points.
Coronary calcium in veteran athletes
In 2017, a Dutch team published a study in Circulation of 284 men, aged 55 on average, who played competitive or recreational sport (abstract on PubMed). They had a coronary CT scan and were grouped by lifelong exercise volume.
| Group | With coronary calcium | With plaque |
|---|---|---|
| Under 1,000 MET-min per week | 43% | 56% |
| Over 2,000 MET-min per week | 68% | 77% |
The most active men had more calcium and more plaque. Their plaques were different, though: fewer mixed plaques (48% vs 69%) and more often only calcified plaques (38% vs 16%). The authors read this as a more benign plaque composition, which could explain why endurance athletes tend to live longer despite carrying more plaque.
Atrial fibrillation and endurance exercise
In 2021, a meta-analysis in the British Journal of Sports Medicine compared athletes with non-athletes (abstract on PubMed). The risk of atrial fibrillation was about 2.5 times higher in athletes (odds ratio 2.46). It was higher in mixed sports than in pure endurance sports, and higher in athletes under 55 than in older ones.
Atrial fibrillation makes the heart beat irregularly. It can feel like palpitations, unexplained tiredness or a drop in performance, although sometimes it causes no symptoms.
What it means for recreational runners
The review focuses on extreme endurance exercise and ultra-distance events, and the authors stress that regular exercise protects the heart. With that in mind, some general advice applies to any runner:
- See a doctor if running brings on chest pain or tightness, palpitations or an irregular heartbeat, dizziness, fainting or breathlessness out of proportion to the effort.
- If you train for ultras or have many years of high-volume endurance exercise behind you, a cardiology check with an ECG makes sense. The European Society of Cardiology has had sports cardiology guidelines since 2020.
- An unusually high or irregular heart rate on easy runs is worth a consultation. To know what is normal for you, check your heart rate zones.
- Building volume gradually and respecting rest lowers the risk of overtraining. There is guidance in the article on weekly running distance.
None of these studies says where the threshold lies beyond which endurance exercise stops adding benefit. The Dutch study uses a cut-off of 2,000 MET-minutes a week, and it only measures associations in middle-aged men.
Limitations
The review adds no new data and its full text is not open access. The studies cited here are observational: they show associations and cannot prove that exercise causes the changes, and the coronary calcium study only included men. The review authors declare no conflicts of interest.
Frequently asked questions
Is a lot of running bad for your heart?
Regular exercise protects the heart. The review argues that extreme doses of endurance exercise, such as ultra-distance training, may be associated with fibrosis, more coronary calcium and atrial fibrillation, although the long-term effects are still debated.
Do runners have more coronary calcium?
In a 2017 study of 284 men, the most active group had more coronary calcium and plaque, but more of it was calcified plaque, which the authors consider a more benign composition.
When should I see a cardiologist?
If you notice chest pain, palpitations, dizziness, fainting or disproportionate breathlessness while running. A check with an ECG is also reasonable if you do endurance exercise at very high volumes.
