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CW: More bad news for the (extreme) endurance exerciser

Dear Endurance Athletes,

Accept an apology in advance. You have endured so much from me.


Let’s at least start by agreeing that I can’t control the data.

Yes, you guessed it. There is unfortunately more bad news pertaining to the deleterious effects of endurance exercise on the human heart.

Again, I am sorry. Maybe re-phrasing the previous sentence will soften the blow. How about this: “Yet another study on endurance athletes suggests that exercise, like everything else in life, has an upper limit.”

Here goes, buckle up.

The study titled, Exercise-induced right ventricular dysfunction and structural remodeling in endurance athletes was published last week in the European Heart Journal.

Researchers from Belgium and Australia enrolled 40 long-term endurance athletes in a study looking at heart function after an endurance race. All subjects were long-term exercisers and were accomplished athletes with above average fitness. They were elite.

By measuring cardiac enzymes (heart injury) and taking ultrasounds (directly seeing heart function) immediately after 4 different length races (marathon through ‘ultra-triathlon’), researchers were able to measure the acute effects of extreme exercise on the heart. MRI scans performed a week later assessed for cardiac scar tissue. (The presence of scar in heart muscle portends trouble because it disrupts electrical signals.)

The main findings:

  • Compared to pre-race measures, right ventricular (RV) function diminished post-race, whereas LV function remained normal.
  • Blood levels of cardiac enzymes increased post race and these rises correlated with the amount of RV impairment.
  • The degree to which RV function decreased correlated with increasing race length and an athletes’ VO2 max.
  • 12% of athletes had scar detected on MRI scans at 1 week post-race. Those with scar reported greater cumulative exposure to exercise and had more RV abnormalities post race.


The authors rightly conclude: “intense exercise causes dysfunction of the RV, but not the LV. Although short-term recovery appears complete, chronic changes may remain in many of the most practiced athletes.”

My take:

I’m not an alarmist, but this study scares me.

First, there are (general) rules in medicine. One in cardiology, electrophysiology in particular, holds that RV damage is not good. Diseases that affect the RV tend to cause electrical instability that may increase the risk of sudden death. (Medical people call such a process, arrhythmo-genic.)

I’m not saying that exercise-related stunning of the heart and scar formation causes sudden death. I’m just pointing out that things that mess with the RV should not be called meek. If I was writing an academic piece, it would read, “the findings of this well-done study are hypothesis-generating and warrant further prospective investigation.”

Second, the data fits a pattern: Longer races and fitter athletes (who are able to sustain higher outputs longer) release more cardiac enzymes and sustain greater RV dysfunction. Those with the greatest exercise history and those who sustain post race RV damage are at greatest risk of developing scar. More was worse.

Third, the findings fit nicely with prior studies. Marathon rats who ran themselves silly—like the subjects in this study—showed similar scar patterns. Also, numerous prior studies in humans (published in peer-reviewed journals) have shown similar patterns of heart injury immediately post race. Other more recent MRI-imaging trials also confirm the presence of scar tissue in the hearts of endurance athletes.

Fourth, and most frightening, in the discussion section the researchers comment on the possibility that heart damage accumulated from long-term exercise may persist even after de-training.


Exercise remains the most effective and safest means to prevent and treat heart disease. The overwhelming majority exercise far too little. In fact, I believe the US suffers from severe exercise-deficiency.

That said, however, accumulating data suggest–at least–the possibility of an upper limit of what the human heart can sustain.

Each study on extreme exercise has its limitations. This one is small. It’s not randomized. And, studying exercise is tough because of the many confounding variables: genetic make-up of individuals, the presence of underlying diseases, and self-reporting of exercise amounts are just a few of many examples. But when taken together en bloc, these ominous trials grow harder for the naysayers to dismantle.

All this is reassuring to masters of the obvious. As it looks like optimal health is born and nurtured through balance.

And there’s little about running marathons or slogging through Ironmans that could be called balanced. Fun maybe, for some.

Balanced? Heart-healthy? No way.


12 replies on “CW: More bad news for the (extreme) endurance exerciser”

Dear John,
Thanks for sharing an interesting study. I have a couple of questions:
1. How much of the elevation in enzymes correlated with signs and symptoms?
2. Was heart scar tissue measured a year after the test?
3. Is scar tissue always bad? I tend to believe that what doesn’t kill, makes you stronger. There are many examples of areas of the body that the repetitive scaring makes that area more resistant to trauma. I understand conductivity and electrical issues in the heart. However, the study did not assess effect of the scars, correct?
4. Was the study a double blind one? Let’s not forget the growing importance of the mind connection in these cases.
Kind regards and thanks,

Jorge – superhealthy two time Ironman finisher and triathlete.

Scar in the heart is never good. It disrupts the smooth flow of electricity in the heart. This can lead to heart rhythm troubles in some cases.

No patients had symptoms–other than fatigue from the heavy exertion.

Scans at one year were not performed.

Interesting but this relates to elite athletes. As a back of the packer do I have the same concerns? What is considered too much training and what is considered optimal? Hours per week? Intensity? I’m not sure how this relates to us mere mortals.
Thank you

Researchers did a study a while back on athletes finishing the Ironman world Championship. The average EF for the athletes was something like 40% after the race. Cleary a case could be made that extreme endurance events can cause the body harm but I am still interested in the 10,000 person study were 5,000 are allowed to live life normally and 5,000 are enrolled into a life of extreme endurance. End point for a person is days to death. I am curious to know which group lives longer.

Thomas Gerlach
Professional Triathlete

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Great summary of a nice study. There is growing evidence that extreme exercise like extreme anything else can be harmful. How much is too much I don’t know, but I know that Ironman falls into that category. Just come and work the medical tent at an ironman event and you will see how healthy the participants look. Saying that, it is hard to discourage such extreme exercise activity when so many obese, sedentary patients abound.

I once volunteered to help with registration at the Sea Otter Classic pro bike race (in CA). With few exceptions, the racers seemed extremely frail, bordering on unhealthy.

Hi Campykid. Thanks for helping out at the sporting events. I think we all appreciate that without help from guys like yourself there would be no event. I would be realy surprised if these guys were actually frail. I have a lot of people say I look realy skinny but my height weight chart scoring is smack in the middle of normal. I also find it strange that when I meet my training buddies for training they all look perfectly normal to me but when I meet them in the street and they are wearing a suit suddenly they look thin. I think what is happening is we are all getting used to the average person being overweight and we rarely see normal weight people so our perspective is altered. They say you are not ready to race untill your mum says you look ill. I once had a couple of secretaries think I was being treated for cancer when I was training for a marathon (probably because I also shaved my head) but I had only lost around 2 kg. I was still 72kg and 181cm and still in the green curve of the height weight chart. I ran a PB and won my age group. The western world should stay away from doughnuts! Henry Szwinto

I did Ironman for 5 years. I was not elite. I notice episodes of what I think was AF when at rest. My HR would speed up very rapidly for 5-10 seconds. I would feel a bit light headed and short of breath during the episode. It would happen maybe once every 6 months or so. Had my heart scanned/checked – they told me I was fine and had “athletic heart syndrome”. This was 10 years ago. I stopped heavy endurance training for 5 years and the episodes went away. In the past two years, I’ve started ramping up again and the episodes have started again. I’ve had 2 this year. Not doing extreme stuff – long run is 10 miles, long bike 40 miles. Should I worry about these episodes?

Hello Guys, I am stunned by the lack of logical thought the doom mongers deploy. After a marathon your legs are tired and physically damaged. You are tired all over and physically damaged. Why is it surprising that the heart is tired and physically damaged? The body will rebuild itself with appropriate rest and we all know that if you don’t give it the rest the body won’t get stronger. So some people forget that or ignore it and hence put themselves at risk but we need to take risk in perspective. These athletes are more likely to die in a car crash on the way to training than when they are running. I agree with Thomas Gerlach, these studies are week unless you have proper controls and what everybody is also forgetting is we would probably rather die out there on the trail than in MacDonalds! I have had AF since I was a teenager and most probably all my life. I was fit but didn’t train excessively back then but I run marathons now. I train more than most but still way below elite athletes. I’m getting a little tired of people telling me I’m damaging my heart and I should give up running or I am damaging my knees or I’m damaging my back. They were all damaged way before I started running. My running helps me stay mobile and sane. I still believe it will help me live longer too. End of rant. Henry Szwinto

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