Heart arrhythmias and endurance sports


As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)


I’m starting to really dislike these jerks who keep studying Swedish cross-country skiers and producing findings that conflict with my worldview… First it was arthritis; now, the researchers studied 47,000 people who participated in the 90-km Vasaloppet ski race in Sweden between 1989 and 1998, looking for associations between the number of times they participated in the race and the odds that they were subsequently diagnosed with arrhythmias (a task made possible by Sweden’s comprehensive national health records). The result (according to a press release describing a conference presentation; the findings haven’t yet appeared in a peer-reviewed journal):

Compared to those who had completed one single race, those who had completed 7 or more races had 29% higher risk of a subsequent arrhythmia. Further, elite athletes finishing at 100-160% of the winning time had 37% higher risk of arrhythmias than recreational athletes finishing at more than 241% of the winning time.

Leaving aside the quibble that “elite” is a bit generous for someone finishing at 160% of the winning time, the findings seem to suggest pretty clearly that extensive endurance training increases the chances of arrhythmia. The biggest differences were found in subjects under 45, and were exclusively associated with atrial fibrillation and bradyarrhythmias, which are considered less serious than the “potentially lethal” ventricular arrhythmias, according to the researchers:

Dr. Andersen summarizes: “Basically, this study shows, that even though physical activity is generally healthy, athletes committed to endurance sports at elite level have higher risk of suffering from a heart rhythm disorder… We emphasize that we do not find any increased incidence of potential lethal heart rhythm disorders. However, this study only compares athletes at different levels and a future large scale study comparing athletes against the normal population would be very interesting.”

The last point is interesting. It does seem increasingly clear that training as an elite endurance athlete is more likely to have an impact on the heart than training at a recreational level — but what about compared to sedentary life? Is this a linear relationship, or a “U-curve” where moderate training produces the best results?

Bottom line: although the press release skips some relevant details (like how common were these arrhythmias in absolute terms?!), I don’t think this changes my risk-benefit assessment. It’s like the well-known trade-off for exercise of any sort: your chance of a heart attack rises temporarily during extreme exertion, but your overall odds of heart attack decline with exercise. In this case, it’s worth bearing in mind the findings from previous studies of the same race: the more Vasaloppets you do, the longer you live. So whatever the downsides of arrhythmias, they’re evidently outweighed by other benefits.

8 Replies to “Heart arrhythmias and endurance sports”

  1. I don’t think this study has to rock your worldview too much if the researchers are including Bradycardia in their results. My guess is it will be the most common type of arrhythmia present in their sample, followed distantly by a-fib–which is not terribly serious unless it is continuous and causes a clot in the atrial chamber(s) leading to PE or CVA. Less frequent will be the heart blocks and ventricular arrhythmias…the researchers even mention these are no higher in their sample than would would be found in a normal population anyway.

    I believe the addition of bradycardia will tend to skew the results as anyone who trains regularly (likely anyone who has completed one of these races is, at least to some degree, a regular endurance athlete) will show a lower heart rate than their sedentary counterpart.

    Bottom Line: I don’t think it’ll be a game changer.

  2. couldn’t agree more, I’m sick of it too ! What they simply fail to do is put things in context. They don’t do comparison studies, they only look at one health parameter/risk and as you said, they don’t look at the results in absolute terms. Yet what people take from these studies is that “endurance exercise kills you” !!

  3. Another perspective that I have read a lot about recently that these researchers do not mention is that although it may be true that elite endurance athletes who have trained for many years at a high level may be more susceptible to some arrhythmias, it is not clear at all whether these arrhythmias affect elite endurance athletes in the same way they would affect a sedentary person. In fact, some of what I have read indicates that there is no evidence it has any negative affects on elite endurance athletes (at least the atrial ones).

  4. I think you have asked all the right questions to illustrate that these findings are probably irrelevant.

    First, these were presented at a scientific meeting, not published in a peer-reviewed journal and therefore should be considered relatively preliminary.

    Second, bradycardia is common in well trained athletes and I have never encountered an athlete where bradycardia caused any ill-effects in an athletes. In older people, sometimes it requires a pacemaker, but it should not be included as an outcome. That would be like studying a cancer drug and saying “this drug increased both the patient’s life-span and their nausea”. Well, yes, clearly, that is what most cancer drugs do.

    Third, atrial fibrillation is a very common arrhythmia, and as you get older and develop other illnesses (heart attack, high blood pressure) the risk goes up steadily (roughly doubling each decade of life). According to the American Heart Association, the risk is about 0.1% per year in people under 40 up to 2% per year over age 80. So, under 40, your risk (according to this study) would increase from 0.1% to 0.12%, with more of an effect if you are older.

    Perhaps some of these questions will be addressed in a full journal manuscript. Regardless, I am not changing my training. The benefits of endurance sport clearly dwarf this (possible) risk.

  5. As a 61-year-old endurance athlete who was recently diagnosed with atrial fibrillation, I’m wondering if athletes are just more likely to experience it.

    My only episodes have been after at least 30 minutes running or 2 hours biking at heart rates episodically approaching lactate threshold. The Holter monitor I’m wearing has recorded nothing, because the cardiologist (a marathoner) says that for now, no running or cycling at speed. As long as my heart rate stays low, my heart rhythms are normal.

    I suspect that if I didn’t run or cycle, I wouldn’t know I had a-fib.

  6. I’m a 45 year-old woman who plans on doing an ironman in the next two years. I’ve finally reached a point where I feel like I can accomplish this feat. (I’ve run several marathons and just completed an 84 mile bike ride.) I’m looking forward to the challenge, the feeling of accomplishment and going beyond my limitations. I’m not a medical professional so articles like this, and others, frustrate and scare me. (Ironically, I was diagnosed with an arrhythmia when I was 29 and my doctor prescribed cardio. exercises, i.e. running. Since taking up running, I have rarely had a flare up.)

    I am grateful for the commentary, will begin training and hope that my heart can take it.

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