CardioExchange Archive

When it comes to exercise, it may be true that you can do too much or go too fast. It might seem counterintuitive, but a new study finds that among cross-country skiers, the risk for having a cardiac arrhythmia is highest in those who race the fastest or most often.

Although lack of exercise is almost certainly a major contributor to cardiovascular disease, the beneficial effects of moderate exercise may not always be extended with more frequent or more intense exercise. Previous research has raised the possibility that a small number of elite athletes may be at increased risk for heart rhythm and cardiovascular problems.

In a paper published in the European Heart Journal, Swedish researchers report on more than 50,000 participants in the Vasaloppet, an enormously popular 90 kilometer cross-country skiing event that takes place each year in Sweden. Previous research has shown that Vasaloppet participants are, not surprisingly, healthier than other Swedes across a broad range of measures.

With nearly 10 years of follow-up, there were 919 cases of arrhythmia. People who completed five or more races and people with the fastest finishing times each had a 30% increase in the risk for arrhythmia compared with the rest of the participants. Atrial fibrillation and bradyarrhythmias were the most common arrhythmias that occurred. There was no difference between the groups in the risk for the most dangerous, life-threatening arrhythmias (ventricular tachycardia, ventricular fibrillation, or cardiac arrest).

“The present study investigates the higher end of the physical activity level scale and shows how very high physical activity level affects risk of arrhythmias,” said the lead author of the study, Kasper Andersen, in a press release. But, the Swedish cardiologist said, it is “important to emphasize that numerous studies have shown that exercise protects against heart disease and numerous other diseases. Our findings should not deter people from exercising, especially as we did not find any increased incidence of arrhythmias leading to sudden death…. We believe that it is generally safe to prepare for and participate in the Vasaloppet races.”

Andersen was cautious in his interpretation of the data: “These findings suggest there is a dose-response relationship: the more races skiers complete and the faster they go, the greater their risk of subsequently developing arrhythmia. However, it is important to stress that this study does not show that the exercise causes arrhythmias, only that it is associated with an increased risk.”