Best of the Best Nordic Skiers May Be at Higher Risk for Heartbeat Irregularities

Jun 18, 2013

Racers line up at the Vasaloppet starting line.
Credit mill56 - Flickr

The scientific community agrees: exercise does a body good. When comparing a sedentary lifestyle spent on the couch versus being an active cross-country skier, the recommendation from doctors is a no brainer: Go grab those skis! Which is a lesson Aspenites have long taken to heart. But a recent study from Sweden complicates the simplistic “exercise is good” mantra that we are used to hearing.

That's the sound of 15-thousand cross country skiers simultaneously embarking on a grueling 90 km course. This is the Vasaloppet in Sweden.

From a helicopter's eye view, this mass of elite athletes making their way across an alpine plateau almost looks like the time-lapse of a glacier flowing down a mountain... there are that many of them, all moving in unison.

If you've never heard of the Vasaloppet, think "Boston Marathon," but for nordic skiing. With it's inauguration in 1922, it's the oldest, and one of the longest "ski marathons" in the world. But its history goes back even farther, all the way to the 16th century, and is steeped in bloodshed, tax revolts, and the story of King Gustav Vasa's heroic escape across the province of Dalarma, the setting for the race. As you can guess, winning the Vasaloppet--or the Vasa--is a big deal.

"Yea, it's a huge feather in your cap."

That's Craig Ward, an Aspenite and former Olympic captain for the 1980 Lake Placid Nordic team. "I was on the US ski team for 8 years." What led me to Craig was new research on cardiovascular health in nordic athletes. A team of Swedish doctors and scientists last week found higher relative risks for irregular heartbeats, or arrhythmias, in the most elite cross-country skiers. Their laboratory was the Vasaloppet.

"What we showed was there was an increased risk of having an arrhythmia by doing more races and doing them faster." Kasper Andersen is lead author of the study. "That was mainly the kind of arrhythmias called atrial fibrillation and bradyarrhtyhmias."

Atrial fibrillation means the heart beats irregularly and too fast, while bradyarrhythmia is when it beats too slow. Though not life-threatening themselves, if chronic, these arrhythmias can eventually lead to blood clots and possible stroke. Among the Vasaloppet athletes, researchers found participants who did the most races were more than twice as likely to develop the problem compared to those who did just one race. Those who finished with the fastest times, were at roughly 20-percent higher risk. So, being the most elite, so to speak, means you’re at a higher relative risk for heartbeat problems.

"We believe that it's a consequence of the training you do to the race that gives you this increased risk. The faster you do it, you would believe you trained more."

The researchers examined all Vasaloppet athletes between 1989 and 1998 who did not have pre-existing cardiovascular disease. Using the national registry system in Sweden, they collected health, wealth, and educational data about the racers for years after their last race, almost 53-thousand skiers in total. Here's another part of the research team, Johan Sundstrom.

"The great thing about epidemiology in Sweden... is that you are able to link people using their personal identification number to a lot of health registries. There really aren't a lot of places you can do that."

Sundstrom said he expects these results would likely apply generally to other elite endurance sports. Earlier scientific studies have shown higher levels of arrythmias in endurance athletes compared to a general population control group, but this one is novel for the sheer size of its data set. Back in Aspen, I asked ex-Olympian Craig Ward what he thought about this:

"What was your reaction to that... were you surprised?"

"I was not surprised at all. In fact, after ten years from being on the US ski team, I had a ventricular tachycardia, an arrhythmia if you will."

We don’t know exactly why elite endurance athletes might be at heightened risk for this condition. One idea, according to Dr. Thomas Allison of the Mayo Clinic, has to do with changes in heart size. Athletes’ high-performing bodies demand lots of oxygenated blood, so the heart grows bigger over time to accommodate this demand.

"Hearts operating at a larger volume, there's more tension developed in the walls of the heart. Increasing its size, it's getting stretched."

And that stretching may disrupt some of the heart's elasticity, creating zones where arrhythmias might occur. I asked Dr. Allison what he plans to do with this new knowledge when seeing patients.

"I would inform them of the risks, but I certainly wouldn't tell them they could not keep doing this if they wanted to, they just have to recognize there may be a small risk of developing these arrhythmias."

Johan Sundstrom of the study, agrees. "While these skiers may have an increased risk of atrial fibrillation or arrhythmia. I'm really cautious to not get this study in the wrong perspective." In fact, in a previous piece of Vasaloppet science, researchers found the skiers who did the race had lower mortality than the general population.

Still, this study does paint a clearer picture of what researchers have long thought to be true: there likely exists some optimum level of endurance exercise, beyond which there may be a little or no benefit, or even detriment. Put another way, sometimes too much of a good thing can be a bad thing.

But don't forget, still, that it's a good thing.