Researchers conducted ECGs, pulmonary function tests and exercise assessments, as well as echocardiography over a period of 30 years on a group of 122 cross-country skiers.
When participants found to have the cardiac arrhythmia due to structural heart disease or other known causes were excluded, the researchers found that 13.8 per cent of the skiers had lone AF.
The mean age of onset of AF in the skiers was 58 years.
In comparison, the prevalence of AF in general population studies has been found to be as low as 0.5 per cent, rising to 15 per cent in men over 75 years.
The study identifies two characteristics which may predict the risk of AF in skiers: bradycardia and an enlarged left atrium.
Principal investigator Dr Jostein Grimsmo said it was not clear why some athletes develop AF while others do not.
'Genetic factors predisposing to "athlete's heart" with enlarged cardiac dimensions and a slow heart rate may be important risk factors,' he said.
'While it may be that prolonged endurance training over many years may not always be good for the heart, we do not yet have sufficient evidence to make specific recommendations.'