Excessive amounts of hard training could be fatal. New results from a study originally carried out in 1976 show that 150 entrants to the Birkebeiner Cross-country ski races are at higher risk of suffering from a heart attack or stroke than the rest of the population.

Surprising

Jostein Grimsmo – specialist in sports medicine at the Feiring Clinic – says he’d heard reports that skiers were particularly susceptible to cardiac fibrillation.

He decided to test it out, and put competitors from 1976 on the treadmill again. Grimsmo was surprised to find almost 17 percent had it.

“It’s the highest number that’s ever been found amongst a single group of people to date,” he tells Aftenposten, saying it falls to 13 percent if you remove other causes such as heart failure or high blood pressure.

Most participants were extremely fit, and had both a larger and thicker heart muscle – a so-called sports heart.

Negative

The risk is 0.5 percent amongst the general population, rising to 15 percent for those over 75.

But prolonged physical exercise can increase the risk of cardiac fibrillation. 80-90 percent of those tested had an enlarged heart atrium, according to Grimsmo.

“It seems that being best trained, with the largest sports heart and lowest resting pulse rate, can have negative long-term effects,” he says.

Age

The risk of developing cardiac fibrillation is higher the older you are, though Grimsmo says he can’t tell if it’s more dangerous to begin prolonged training at a younger age.

“The heart is more elastic and contracts more easily if you keep up the training when you’re younger. But this doesn’t happen as people get older, suggesting the risk is higher the harder, and the more you train.”

Grimsmo does suggest the study is not designed to give couch potatoes an excuse to avoid physical exercise. He recommends common sense.

“We encourage people to work out a lot, but it could be that high-intensity training and tough competitions aren’t the best for people 60 and over,” he says.

Cardiac fibrillation can cause transient heart failure, or at worst, a stroke.