Long-term, high-intensity athletic training might raise the risk for irregular heart rhythms, called arrhythmias.
Exercise remains essential for overall heart health.
Those who train for long periods also face an increased risk.
Endurance athletes who train and race frequently may experience a high rate of unusual heart rhythms called arrhythmia, found a new study on cross-country skiers. Arrhythmia, which are often harmless, can sometimes lead to strokes and other serious problems.
Experts remain unsure what to make of the results. Exercise is known to prolong lifespan and to improve all sorts of measures of health, including the heart. And certain kinds of arrhythmia, a type of flutter called atrial fibrillation, are very common.
Still, the study suggests there may be a point at which a lot of training becomes too much. At the very least, serious athletes should be aware of the potential for their hearts to behave strangely.
"I would be worried if people thought cross-country skiing, for example, to be dangerous. That would be an unlucky headline," he said. "We're looking at extreme amounts of training. Most people need to get off the couch and exercise a little bit."