Men who perform well in the cross-country ski race Vasaloppet are at increased risk of having abnormally low heart rates and pacemakers later in life. However, the researchers behind the study did not uncover any link to increased mortality, rather the opposite—the skiers lived longer than the general population.

It has been recognized for some time that prolonged and intense exercise can lead to low heart rates. However, it has not been recognized until now that it can also increase the risk of abnormally low heart rate, known as bradycardia, or the need for a pacemaker.

A new study based on the Vasaloppet register shows that men who have participated in Vasaloppet are more likely to suffer from bradycardia and need a pacemaker than the general population. The risk also increased with the number of times they participated and the speed at which the race was completed. The findings are published in the journal Circulation.

“We wanted to obtain a measure of how fit they were, so we also looked at how many races they had taken part in and how quickly they completed it. We could then see that the risk of both pacemakers and bradycardia increased: the more times and the faster they completed it, the higher the risk,” explains Niclas Svedberg, first author of the study.

Prolonged and intense exercise can affect the cardiac conduction system, the system that sends electrical impulses and controls heart muscle contractions. It is this change that researchers believe can lead to abnormally low heart rates and the need for a pacemaker. However, although the skiers had problems with their heart rate, no link was found with increased mortality.

Svedberg, doctoral student at the Department of Medical Sciences at Uppsala University and Senior Consultant in Cardiology at Falu Hospital.

“It may be that a lot of exercise over a long period can lead to an increased risk of needing a pacemaker. But you shouldn’t be afraid to exercise, as it has so many other positive health benefits. Those diagnosed with a bradycardia diagnosis or pacemaker did just as well as the other Vasaloppet participants in the study, and much better than the normal population,” continues Svedberg.

No increased risk for female Vasaloppet participants

When assessing the female Vasaloppet participants, there was no association between Vasaloppet participation and an increased risk of bradycardia or pacemakers. According to the researchers, this type of study cannot give an exact answer to this. The data is based on skiers who participated in Vasaloppet between 1989 and 2011. There were more older men in the study group. In the early years of the event, there were few female Vasaloppet participants. In total, women made up only 40% of the entire cohort.

“We can speculate as to whether there are physiological reasons or whether women’s exercise patterns differ from those of men. It may also be the case that more women than men started attending Vasaloppet in later years, meaning they have not had as much exposure to intensive exercise as the men,” notes Kasper Andersen, one of the authors of the study.

Previous studies on the Vasaloppet register have shown that men who participate in the race also have a slightly increased risk of atrial fibrillation. Again, there was no increased risk for the female skiers.

“So far, we have not found any negative consequences of sport for women,” says Andersen.