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Research Suggests More Damaging Effects Of Endurance Exercise On The Heart

Dear Endurance Athletes,

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

Sorry.

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.

Ouch!

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.

Conclusion:

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.

*This blog post was originally published at Dr John M*


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4 Responses to “Research Suggests More Damaging Effects Of Endurance Exercise On The Heart”

  1. This was very helpful information, John. I was just on the verge of making regular marathoning a goal (much to the chagrin of my fiance – who kept insisting that it was “overkill” and that he didn’t want to become some kind of running widower). This data gives me pause – and the course correction might even save my life. Looks as if moderate exercise (with the occasional half marathon at the upper limit) is the healthier way to go. ;-) Thanks!

  2. Jonathan St. George says:

    I have to say I agree with you that for many reasons extreme endurance sports of any kind place demands on the body that, despite the fitness of their participants, are not necessarily beneficial for long term health. I do take issue with you interpretation of this study. This is not my area of study, but I am always skeptical of making any real life assertions on data that have no clinically relevant outcomes as end points. To make use of this study in a discussion of the risk/benefit of endurance sports we need epidemiological data about elite athletetes and heart disease deaths or disability. If they are dropping dead or needing cardiac interventions at a higher rate than the overall population then perhaps this is the jumping off point for an area of research that matters. I would even postulate that in our focus as doctors on disease we know little about health. Perhaps these findings are in fact beneficial behaviors of a heart “restoring” itself after an extreme event and that the increased temporary “dysfunction” is in fact a heart that has gotten best at this restorative behavior. There is too much we do not know in this area. If there is more data to the contrary I would like to know. Sincerely Jonathan St. George MD

  3. DrJohnM says:

    Thanks for commenting Val.

    I agree with your fiance on half-marathons. They are plenty hard. In fact, their ‘hardness,’ wore me down and contributed to my cycling addiction. People don’t realize this, but the pain that it takes to exercise at threshold–10k pace–is brutal. I still remember dreading the sensations of trying to hold my threshold pace for the extra 6.9 miles (13.1-6.2) of the half. Hardness to me, is about the effort level, not the distance.

    I also don’t think running one marathon is unreasonable. To be in the club. Chicago 1995 was my entree–and exit from marathoning.

    JSG,

    You are right to point out the importance of considering hard outcomes in scientific research. Surrogate measures have led so many astray. (Think, drugs that raise HDL and all the non-statin-LDL-lowering agents.)

    Even if extreme endurance exercise inflamed people to the point of poor health, it would be hard to show a difference in hard outcomes like death. This is because the comparison group would be ‘regular’ people. And regular people, in general, aren’t fairing so well. At least not the regular ones who come to my office. This study will not be done, but imagine comparing the cohort of people who exercise 30-60 minutes per/day, eat wisely, read books, contribute to society and go to bed on time to those who yearn to ride across America, run Death Valley or heaven forbid, be called an “Ironman.”

    Now for real life. Why are their so many athletes with AF? And what about that scar in the ventricles?. Or that calcium in the coronaries of marathoners? Geez. It’s scary. Unknown. That, combined with my avocation, is why I find it so interesting to write about.

  4. Marathoner says:

    I’ve been reading up on recent studies regarding endurance running and heart health (for reasons my nickname should make clear), and, being a complete medical novice, have some (naive) questions for you:

    1) The heart is a muscle, so I assume that it responds to intense stimulus (exercise) in a similar manner to other muscles. When I run hard, my muscles suffer microtears (scarring), swell and feel weakened as they go through the healing process. But this cycle of damage and recovery is essential to making strong muscle tissue. Reading the article you cite, I note that the RV weakness, scarring and swelling (all of which are noted as temporary, unless the stressors are repeated until the problems become chronic) of the heart seem remarkably parallel to muscular reactions to intense exercise. Is there a qualitative difference? Might the swelling, tears, and weakness focused on as signs of heart injury actually be part of the process of strengthening the heart, since these problems heal (like muscle tissue) relatively quickly? With muscles, we say, there are injuries (the little tears of a hard workout, which are necessary), and INJURIES (debilitating big tears, pulls, strains etc.). Are the injuries these authors investigate not of the first type?

    2) I note that many are reading these authors’ findings along the lines of “endurance running is bad for your heart,” but where are the essential qualifications/explanation of the mechanisms? If indeed the RV weakness, related swelling and scarring are “bad for the heart” and not actually part of the process of strengthening the heart muscle, still, many questions remain unresolved. Is the distance itself the problem? Is it the speed at which the distance is done? Is it distance/speed relative to conditioning? (By this, I mean that elite athletes often “over-perform,” enduring high levels of pain to reach new bests, and also that non-elites often try to ‘prove something’ by biting off more than they can chew [the marathon].) Is a marathon (as you assume above) necessarily “too much”? I’d argue with you here that run at a comfortable pace and with proper preparation (slow buildup of endurance), 26.2 miles is not actually so stressful. I ran 3 of them in 6 weeks this fall, without any apparent negative health effects. In fact, I didn’t even need any rest time time after 2 of these marathons, but kept right on training as though they were just another weekend run. (I’m 45 and no superman, but I prepared very well, building up over months.)

    3) I cannot mesh these findings on the negative influences of endurance running on the heart with the numbers that suggest that distance runners have far, far feer heart attacks than the general public. In place of raw numbers, far too much is made of anecdotal cases (Jim Fixx, Alberto Salazar) where family history led to serious runners experiencing heart attacks, as though these are proof that running is bad. Where is the correlation between endurance running and heart problems in terms of actual numbers? Yes, I know that people die of heart problems in marathons every year, but where is the statistical correlation between marathon running and heart problems?

    Thank you.

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