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How Do Intensive Endurance Sports Affect the Heart?

The benefits of sport are well known, but the risk of extreme sports on your heart health is less well known.

The principle of "use it or lose it” applies to the heart and exercise. Like all muscles, the more you work your heart, the bigger and stronger it gets, especially with moderate activity, where the intensity corresponds to 60–70% of the maximum possible effort. This is called endurance training, a type of training that over time is good for overall health and strengthens the heart. It stimulates blood flow and more oxygen is supplied to the organs and muscles. In short, the entire body benefits from endurance training. Running, cycling, cross-country skiing, and any other sport can produce these health benefits.

However, training for lengthy, concentrated periods at a level that is too intensive may damage the heart's ability to pump. Over time, too much physical exercise can significantly increase cardiac output and blood pressure. This physiological response from the body may lead to atrial fibrillation.This common and serious form of arrhythmia, which is an irregular heartbeat, affects over 30 million people worldwide and mainly causes heart palpitations and shortness of breath.

Although this medical condition is more likely to occur in people over the age of 60, alongside cardiac risk factors, such as high blood pressure, heart failure, and heart disease, it occasionally affects younger people with no sign of heart disease or other health problems. In the general population, the prevalence of atrial fibrillation in individuals with a healthy heart, known as lone atrial fibrillation, is between 2% and 10%.

Running is Good for Your Heart

According to a longitudinal study conducted in the 1990s, just over 5% of the orienteering runners studied appeared to be affected versus 0.9% in the control group1. Researchers conclude that these results were surprisingly high for middle-aged subjects who had no particular predisposition to this type of heart arrhythmia. In addition, a retrospective study showed that 63% of patients with lone atrial fibrillation played sport for at least three hours a week.

Researchers also looked at former professional cyclists who signed up to the Tour de Suisse cycling race at least once between 1955 and 1975, and golfers who had never taken part in an endurance challenge. Result: the prevalence of atrial fibrillation was 10% among the cyclists versus 0% among the golfers.

Intensive cycling also appeared to affect the anatomy of the elite-level athletes, since it was noted that their left atrium and ventricle were enlarged compared to a normal heart. Yet, left atrial enlargement may be a predisposing factor for more frequent episodes of atrial fibrillation. Whether you play sport or not, left atrial enlargement is linked to the development of lone atrial fibrillation in the general population. How intensely sport is played is important, since it appears that individuals are more prone to this medical condition after several decades of regular, sustained sports practice.

The symptoms of atrial fibrillation have a negative impact on athletic performance and quality of life. Reducing the amount of high-intensity sport, or taking a break from practice altogether, may be recommended as first-line treatment.

Since 1998, studies have shown that ablation, a surgical procedure to treat atrial fibrillation using a catheter, enabling patients to return to physical activity, is more effective than pharmaceutical treatment using antiarrhythmic drugs. Ablation burns the heart tissue causing atrial fibrillation, in order to prevent rogue electrical currents traveling from the pulmonary veins to the upper chambers, the right and left atria, of the heart.

1 Silbernagl, S., Despopoulos, A., Draguhn, A. (2018). Taschenatlas der Physiologie. Thieme. 9th edition. Hegner, J. (2015). Training fundiert erklärt. Ingold. 2nd edition