This article is mainly about cycling, but it is a little scary. I will say that I am a 'low mileage' ultra runner if that makes any sense.  Plus these days I don't get the heart rate up very high during training runs.

But the scariest part of all is my running buddy just had a pacemaker put in, mainly do to AF.  He's not running for a while while he is recovering from the operation, for obvious reasons.

http://velonews.competitor.com/cycling-extremes

I think I am like you Sandy seeing that maybe to some I run a lot of miles for the group around here but in reality I'm not a high mileage person nor do I put much emphasis on speed these days in a V02 max sense. So I feel I'm pretty safe, and not too concerned but seeing I'm halfway through my 50's stuff like this gives me pause.

I once was in the hospital for a heart situation diagnosed as acute viral pericarditis. I never thought of myself as invincible being an ultra runner but it still was surreal sitting there in the ER as they treated as potential patient for cardiac arrest.

Well, long term there will be hiking and golf in my future.

Interesting reading. I thought about dissecting the article and bringing forth some interesting points in rebuttal, but I don't have the time to go that in depth right now.

What I will point out is that after a 20 year career as a paramedic, and during that time seeing a large amount of A-Fib patients and sudden death from cardiac arrest, I can not remember ever treating a older endurance athlete for any dysrhythmia or cardiac arrest.  I have treated one high school athlete for Supra Ventricular Tachycardia (SVT).  Almost all of my cardiac arrest or dysrhythmia  patients are older (>50 ),  out of shape, sedentary and typically overweight. Among the middle age range (25-50) they are almost always obese or have other bad lifestyle issues such as drugs, or alcohol abuse. I have run into some who have needed a pacemaker inserted before they are 25 leading me to think that they have a congenital disorder.    It seems to me if a older endurance athlete has a average or above average risk of AF then I should have seen at least a few along the way.

In the case of SVT I have known several people who are moderately active who have to deal with it. They developed it early in life and stress is more of a trigger for it than exercise.

I don't really have a problem with doctors pointing out that we as serial exercisers have risks for cardiac disease. We do, and need to be aware that the fluttering in our chest, the dizziness etc.  may need to be checked out.

I can tell you from personal experience that sedentary people read articles like this and use it as an excuse to not become active.

Racing/hard training can be unhealthy, and bike racing involves lots of anaerobic efforts in addition to long hours in the saddle .... running does as well. I do not race or run/bike huge mileage, but I do long rides and runs on accassion

I will only say that I run/ride for fun, push myself on some occasions and try to be sensible in my approach. Lately I have been not doing as many intervals and just trying to get some baseline fitness back. If and when I do I am sure I will start pushing it a bit more ....

During one of my double centuries we assisted a ride who had a heart attack on the backside of Mt. Hamilton and died on the scene. He had a history of heart trouble in his family, and was exceedingly fit. As someone said, cannot ride/run away from genetics.

There are some more thoughts that crossed my mind.

Not trying to minimize a potential problem, or explaining it away.

- Maybe athletes, and especially endurance athletes, have a higher relative risk for AF because they have a lower risk for congestive heart failure, diabetes (and causes of death related to it), and stroke. I mean that in the "general population", there are just more individuals dying from these causes, so  the group of endurance athletes is a select entity of individuals who rather die from other causes, and because congestive heart failure, diabetes and stroke are among the leading causes of death overall (cancer would be another one, but if someone has cancer, it's less likely he's an endurance athlete because he'd likely quit or interrupt his endurance training at least for a while), bang, all of a sudden, the endurance athletes are at higher risk for other causes of death, including AF.

- The article talks about endurance athletes who seem to be "addicted to sports". Not all endurance athletes fit this description.

If someone is "addicted" to their endurance training, he's likely to keep exercising hard even when he's ill, with a fever, and it is very well known that this can lead to heart conditions (I don't know about AF, though). It is easier to bike (even hard) through a bout of the flu than it is to run through it, just because running is a bit more exhausting than biking, and while you couldn't run, you might be able to bike with a fever. So it is not a big surprise that especially bicyclists might be more prone to developing heart conditions, like scarring or fibrosis, over their years of active training.

- Bicyclists might be at higher risk for overloading their hearts for decades because bicycling does not usually cause joint issues or pain like running does in some (many) people and which makes people quit. Therefore, bicyclists are more likely to maintain active endurance training for decades than runners. The longer the period of hard training, the more likely AF develops. Therefore bicyclists might have a higher risk for AF than runners.

- Bicyclists, especially the die-hard, old-school endurance guys, who are in their 50's and 60's now, have a reputation to keep training hard. They might not easily accept (and modify=mellow down their training accordingly) that they are not in their 20's any more (where it is easier for the heart to heal completely without scars from overload). So they keep doing what they've always been doing, causing them to develop more scars, etc., which increases their risk for AF.