Endurance athletes have a four times higher risk of irregular heartbeat, and this may be why

[medicalxpress.com]

"Even after a single mountain marathon, researchers have seen short, frequent spikes in inflammation and a transient slowing of the electrical conduction in the atria. Over time with repeated events and training, these cardiac stresses could be what cause an increased heart chamber size and scarring (pathological cardiac remodeling)—increasing the risk of atrial fibrillation."

Mountain marathon.... The mere thought of that sounds painful.

The exertion is only part of the problem. As a person who has run numerous foot races at various distances, including half and full marathons, dehydration and low sugar and electrolyte levels are a constant problem. If the athlete is not careful, he/she could even enter a race somewhat low on both water and electrolytes already, say from a late night pre-race party the night before, or even from a training run the previous day or two and have forgotten to rehydrate or to rest properly. Or, with the logistics of the race, they forego sleep and have to travel, making it a stressful day trip. All these pursuits, 'lifestyle' choices, add up over 20 years.

I don't think all those endorphins save a person from health problems. They may make you feel exhilarated a bit, but they don't make up for errors in system management.

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Carey
Mountain marathon.... The mere thought of that sounds painful.

I was that guy - though only a mountain 1/2 marathon, but it gained 7,800'/2,400m topping out at 14,100'/4,300m. It was training for my 9th entry of this event that preceeded my first afib episode.

However I never did 7-10x the guidelines for training as mentioned in the links on the studies. Much less than that.

As I've posted before, I learned that doing long duration activities at a Zone 2/nasal breathing effort level was OK. It is doing long duration activities at a higher intensity that is my trigger. However, high intensity activities, like sprint interval training (SIT) or HIIT - high intensity interval training (sprint is all out, high is s bit less) for short durations is OK. I additionally do hypoxic/hyperoxic training layered on top of SIT & HIIT. I hypothesize that long duration at high intensity metabolically creates a lot of oxidative stress that causes issues.

I've always wondered why endurance athletes think what they do is so healthy. I've always looked at it like a car. If you put on too many miles, things simply wear out. No mystery why. If you don't put on enough miles, seals dry out, parts seize, and nothing works well. Again, no mystery. So what you want is a happy medium.

This is not to say you shouldn't do endurance sports if you love them. I have in the past, and it was very rewarding. But more for me than my heart.

Jim

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mjamesone
I've always wondered why endurance athletes think what they do is so healthy. I've always looked at it like a car. If you put on too many miles, things simply wear out. No mystery why. If you don't put on enough miles, seals dry out, parts seize, and nothing works well. Again, no mystery. So what you want is a happy medium.

To your point, the following was written (in 2003) in the introduction to Hans Larsen's book, "Lone Atrial Fibrillation, Towards a Cure," by the late French EP researcher,Professor Philppe Coumel, MD.

"When asked what must be done to prevent further attacks, I usually tell my patients it all depends on them and that the answer lies in their own observations. This is, in particular, the case for sports, whether on an occasional basis or with the major issue of professional training; excessive training is harmful when it exaggeratedly modifies the ANS balance beyond the sympathetic and parasympathetic physiological values It is a major mistake to think that the man in the street must be as trained and fit as the professional sportsman. Any common sense driver knows that if he wants to make his car last he must avoid handling it as a rally or Formula I driver."

Any common sense driver knows that if he wants to make his car last he must avoid handling it as a rally or Formula I driver."

Perfect! I'm old enough to remember when marathons were run mostly by elite runners, but now just anyone can enter them. Then came the weekend triathlete, something I've seen close up as a safety escort, occasionally pulling swimmers from the water who were clearly beyond their limits.

The message back then was more is better, and it persists today, even as evolving science says otherwise.

Jim

So, what percentage of endurance athletes end up with afib? I would guess, a pretty small percentage.

I was an Olympic level swimmer that trained in the summertime between 4-6 miles a day - ended in 1968. My events were 100 and 200 meters, but that was the training program at the time. Distance swimmers, 400 to 1500 meters did a lot more. If I had known that I would get afib as a result of my training, it would not have changed a thing.

I was an endurance athlete pretty much my entire adult life. I used long lunch hours to run between 5-8 miles daily, and I ran 20+ km most Sundays....pretty much without fail, for 27 years. I only developed AF late in life, and the cardiologist concluded that the problem was OSA, not the running I was still doing three/four times each week, or the two or three cycling sessions I did, all with fairly stiff intensity at times, so that I could compete in local races. Still, their derived figures didn't come out of thin air. There's something clearly. And it might just be overuse. Or maybe poor recovery or insufficient/incomplete recovery.

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Ken
So, what percentage of endurance athletes end up with afib? I would guess, a pretty small percentage.

Certainly not a majority, but the number is nontrivial based on the number of endurance athletes who I meet and I randomly find out they have afib. This includes Carey's favorite EP/writer, who happens to also be a cyclecross athlete with afib (and I'm intentionlally not naming).

lol... That's okay, George, I promise I won't fly into a rant if you simply name him.

I knew he was a cyclist but didn't know he competed in cyclocross. But does he actually have afib? I read the piece where he described his episode, and then never heard another word about it. It's always been my impression that he had a single, isolated episode during a bicycle ride. I would always interpret something like that as a one-off event, probably due to dehydration and electrolytes. But maybe he made more public that I haven't seen.

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Carey
lol... That's okay, George, I promise I won't fly into a rant if you simply name him.

I knew he was a cyclist but didn't know he competed in cyclocross. But does he actually have afib? I read the piece where he described his episode, and then never heard another word about it. It's always been my impression that he had a single, isolated episode during a bicycle ride. I would always interpret something like that as a one-off event, probably due to dehydration and electrolytes. But maybe he made more public that I haven't seen.

I read it years ago, like you. Here is a version in "The Haywire Heart" book.

"EVERYONE’S DIFFERENT, but my case of atrial fibrillation (AF) is instructive about what athletes may face. It happened to me at age 48. I was training hard for the upcoming summer bike race season. My team and I were putting in long training miles, race efforts, and threshold work. We were racing on the weekends and training during the week. Then I broke my ribs in a crash. If you have ever broken a rib, you know how much the injury slows you down. Breathing hurts, sleeping hurts, and sneezing is like an electrical shock coursing through your body. But there was a third component that led to my AF. On top of an intense training load and a rib injury, I was also working full-time as an electrophysiologist. It’s fascinating work, but it’s also exhausting; among other things, it involves standing in the laboratory draped in a heavy lead apron for hours at a time, walking repeatedly down the long halls of the hospital, and continuing to make patient rounds. Being a cardiologist is demanding in itself, but with a rib injury and fatigue, it was fertile ground for the development of AF. One hot summer day after the crash, I was on a training ride with my teammates. That day I had taken no pain meds, and my ribs hurt a lot on the ride. But I was doing okay. I was rotating in the line, taking my turns. Then it happened. We were 40 kilometers from home when I noticed an abrupt onset of breathlessness and an utter loss of power. It was more than the heat; it was something else. My heart rate monitor showed funny numbers. The beats were irregular, and any slight rise in the pavement caused my heart rate to spike much higher than normal. I had to let the ride go on without me. Moments before, I was pulling through easily. But now I couldn’t hang with the group. A friend stayed with me, pushing me up hills. When I finally got home, I told my wife that I thought I was in AF. She is a hospice and palliative care doctor, so for her, AF is hardly alarming. She felt my pulse and seconded my suspicion. “You have an irregularly irregular pulse,” she said. “Yep, you have AF.” Since I am a cardiologist, I decided to confirm the diagnosis myself. I showered and dressed and went to my office to do an ECG, an echocardiogram, and some simple blood tests to check my thyroid function. The tests showed that my heart was fine, other than the rhythm being in AF. That night, I went home and rested. My partner in our practice called in some medication for me. I swallowed the pills and went to bed preparing myself mentally for a day of tolerating the fibrillation and irregular pulse. I figured I’d do a full day of work and then get cardioversion (shock) afterward. The next morning, I woke up without the butterfly sensations in my chest. My pulse was regular. I was back in sinus rhythm, and I felt a small hope that I was in the clear. I took Flecainide (a drug to stabilize heart rhythm) for a few months, a regimen I prescribe for my patients. My heart improved, but it wasn’t exactly smooth sailing. Over the next year or so, I experienced frequent skips, jumps, and flutters (doctors label them “palpitations”) of the heart rhythm. I could feel them in my chest and throat. They occurred at rest and when I rode. On two other occasions in the following months, I had a few hours of AF episodes. In retrospect, I should have seen the signs. I was injured, I was training excessively in the heat of summer, and I was still trying to work full time. What I should have been looking for was balance; it should have been obvious I was asking too much of my body. Instead, I kept pushing myself to continue my routine—my “normal.” But of course I was anything but normal by then. Warning symptoms If my case has any instructive use, it should be to demonstrate that there are plenty of warning signs of trouble. The key is to heed them. But what are they? And what should you be looking for in yourself? There are two types of symptoms to worry about. Both fall into the category of “not normal.” Your immediate sensations are a good guide. You have probably been training for many years, if not most of your life. Those years of training have given you a good sense of what “normal” feels like. What you are looking for is anything that falls outside the boundaries of normal. For example, a brief flutter in your chest on a ride is probably nothing; nearly everyone gets one from time to time. A flutter that won’t go away, however, is cause for concern. A sustained irregular heartbeat is an abnormal feeling that should set off an alarm. Sensations that are not normal include Racing heart: any sustained racing of the heart that won’t go away. Chest pressure or pain, especially pressure or pain that worsens during exertion. Labored breathing: difficult breathing that is out of proportion to effort (everyone breathes hard when climbing hills or sprinting). Fainting or near-fainting: anything more serious than the everyday lightheadedness you might feel after a hard effort. These symptoms are serious warning signs that should alert you to possible trouble. Sustained chest pressure or chest pain warrants a call to 911. All others warrant an appointment with your doctor, sooner rather than later. If you experience these symptoms, you should stop training until you can be evaluated by a professional. Secondary warning signs include sensations that are not normal but usually less worrisome, including Palpitations: skips, jumps, or flutters of the heart rhythm.

Consistently low power: A decrease in sustainable power is the real warning sign here. There are lots of reasons for low power output, including natural variability, overtraining, and medical conditions. Usually it’s the first two. But if your sustainable power drops, take note. Excess fatigue: Like low power, generalized fatigue can be caused by many factors. In fact, fatigue may be one of medicine’s most nonspecific symptoms. Causes range from poor sleep or overtraining to a host of specific medical conditions. Excess irritability: Irritability is often a sign of overtraining or inadequate nutrition, but patients with arrhythmia or other medical conditions often say they are irritable. Spouses sometimes notice this symptom first. When should you see a doctor? Sustained racing of the heart, chest pain, difficulty breathing, or fainting are symptoms that mandate a formal evaluation by a doctor. The four less specific symptoms mentioned above—palpitations, low power, excess fatigue, excess irritability—may warrant a doctor’s visit, too. But those symptoms are less worrisome. Before you see a doctor, try some simple things first. Skips of the heart rhythm, low power, fatigue, and irritability often improve with rest and nutrition. Although many athletes find any period without exercise challenging, either a short period of rest or an even longer period of prolonged rest may resolve the symptoms. Another thing an athlete with the less worrisome symptoms can do before going to the doctor is to pay close attention to nutrition. This means not only eating enough healthy food, but also abstaining from the following irritants to the heart."

Case, Christopher J.; Mandrola, John; Zinn, Lennard. The Haywire Heart: How too much exercise can kill you, and what you can do to protect your heart (pp. 125-130). VeloPress. Kindle Edition.

I don't recall where I read it, but that's much more detailed than the version I read.

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Carey
I don't recall where I read it, but that's much more detailed than the version I read.

I think I first read it in a blog or article 13-14 years ago. He went into more detail then about being apprehensive about taking flecainide for the first time. I believe it was in this period that he wrote about being physically quiet after taking flec PIP to lower the risk of 1:1 flutter. This is something I adopted subsequently, for the most part.



Edited 1 time(s). Last edit at 12/18/2025 08:00PM by GeorgeN.

I have mixed feelings about Mandrola. Given his self-described moniker as a medical contrarian, I think his viewpoints often add helpful context to a lot of cardiac issues, even if some of his conclusions are questionable. And he certainly is not afraid to say things other EPs might not be willing to say in pubic.

But I do agree that his single AF episode, induced under extreme exercise conditions, is a different animal than the progression and treatment of AF most here experience. And it may very well have influenced his entire lifestyle-centric and anti-ablation stance, something you would hope an experienced EP would be aware of when generalizing from personal experience. But then again, confirmation bias often spares no one.

Jim



Edited 1 time(s). Last edit at 12/18/2025 06:50PM by mjamesone.

GeorgeN,

I am in the same boat. Very high level pool and open water swimmer. Age 72. I miss the competition - especially because others my age can still push themselves. After more than 1-2 minutes of higher exertion exercise (>110 bpm), I have to stop.

I read your reply about what you do now and I have a similar routine. Have you investigated what is possible so you can return to higher, longer periods of higher intensity exercise?

Just wondering if my racing days are over....

Thanks

Paul