Moderate Endurance: A Friend to the Heart
It is said that the heart only weakens if it is not used. Like all muscles, it grows stronger with exercise, especially when engaging in moderate physical activity—that is, activity at an intensity of 60–70% of maximum effort. This is known as endurance training—a type of sustained exercise that is beneficial for overall health, and for the heart in particular, as it teaches the heart not to race. Blood circulation is stimulated, organs and muscles receive more oxygen—in short, the entire body benefits. Running, cycling, cross-country skiing, or any other sport can provide these health benefits.
High-Intensity Endurance Training: A Risk of Atrial Fibrillation
However, people who string together long training sessions at too high an intensity risk damaging their heart. In fact, excessive physical exertion can, over time, significantly increase cardiac output and blood pressure. This physiological adaptation, however, is itself likely to lead to atrial fibrillation. This common and severe form of arrhythmia—that is, an irregular heart rhythm—affects more than 30 million people worldwide and is primarily characterized by palpitations and shortness of breath.
While this condition usually occurs in people over the age of 60, in association with cardiac risk factors such as high blood pressure, heart failure, or coronary artery disease, it can also affect younger individuals with no underlying heart conditions. In the general population, the prevalence of atrial fibrillation in a healthy heart—known as idiopathic (or, in English, “lone AF”)—ranges from 2% to 10%.
What Studies Show Among Endurance Athletes
According to a longitudinal study conducted in the late 1990s, slightly more than 5% of orienteering runners were affected, compared to 0.9% in the control group1. The researchers concluded that this incidence is surprisingly high for middle-aged individuals who, a priori, are not particularly predisposed to this form of cardiac arrhythmia. Furthermore, a retrospective analysis showed that 63% of patients with lone AF engaged in sports for more than three hours per week.
Some researchers also studied former professional cyclists who had competed at least once in the Tour de Suisse between 1955 and 1975, as well as golfers who had never participated in an endurance competition. The result: the prevalence of atrial fibrillation was 10% among cyclists, compared to 0% among golfers.
Effects on Heart Anatomy and Management
Intensive cycling also appears to have an impact on the anatomy of elite athletes, as their left ventricle and left atrium are found to be larger than normal. However, left atrial hypertrophy could be a predisposing factor for more frequent episodes of atrial fibrillation. Indeed, whether one is an athlete or not, left atrial dilation is associated with the onset of isolated AF in the general population. The intensity of athletic activity plays an important role, as it appears that individuals are at greater risk after several decades of sustained and regular athletic activity.
The symptoms of atrial fibrillation negatively impact not only athletes’ performance but also their quality of life. Reducing or even discontinuing high-intensity athletic activity may be recommended as a first-line treatment.
Since 1998, studies have shown that pharmacological treatment with antiarrhythmic drugs is less effective than catheter-based surgical ablation of atrial fibrillation, which allows for a return to physical activity. The goal of this procedure is to ablate the tissue responsible for atrial fibrillation, thereby preventing unwanted electrical currents from traveling from the pulmonary veins to the atria (or upper chambers of the heart).
Frequently Asked Questions
Is endurance sports bad for the heart?
No: when practiced at moderate intensity, it is beneficial for the heart and blood circulation. It is very intense and prolonged practice over several years that can, in some people, increase the risk of heart rhythm disorders.
What is atrial fibrillation?
It is a common form of heart rhythm disorder (arrhythmia) that affects more than 30 million people worldwide and is primarily characterized by palpitations and shortness of breath.
How is exercise-related atrial fibrillation treated?
Catheter ablation, which involves treating the tissue causing the arrhythmia, is now considered more effective than antiarrhythmic medications and allows for a return to physical activity.
1 Silbernagl, S., Despopoulos, A., Draguhn, A. (2018). Pocket Atlas of Physiology. Thieme. 9the edition. Hegner, J. (2015). Training Explained in Detail. Ingold. 2nde edition