Sunday, August 16, 2015

Can Too Much Exercise Damage Your Heart?


I get a lot of bike-related articles in my e-mail, mostly via my bike club.  When I get an article from two separate feeds, I know it’s something big.  So it was with a recent front-page story in Velo magazine, “Cycling to Extremes.”  (I read the online version, available here.)  The subtitle:  “Are endurance athletes hurting their hearts by repeatedly pushing beyond what is normal?”

What is normal?  Alas, for American adults “normal” is almost nothing; a CDC survey found that nearly 80% of adult Americans get less than 2.5 hours of exercise a week.

But forget about averages and those who don’t exercise.  The point of this Velo article is that ageing endurance athletes—i.e., guys like me—seem now to be in danger.  The article declares, “In the case of endurance athletes who have competed for years — whose hearts have exceeded the threshold of normal heart rates for decades — going above what is normal defines them.  But it may also be killing them.”

In this post I examine the reactions of my pals to this disheartening article; indulge in some knee-jerk denial; examine some other anecdotal evidence; evaluate the article’s claims on the basis of the literature cited; and (perhaps most importantly) provide a scheme for greatly advancing the study of exercise-induced heart complications among the middle-aged.


My first reaction to seeing this article was, “Oh, crap.  I hope nobody forwards this to my wife.”  (She’s the designated worrier of the family, which leaves me free to pooh-pooh everything.)  But then, I’ve got people depending on me, so I thought I better take the article seriously.  First I looked at how my pals were reacting.  “Hummmm....this is a little scary,” one e-mailed.  Another replied, “Yeah very scary.  I routinely get dizzy when I get up - something that’s happened my whole life but” and here his e-mail ended abruptly.  (Had he collapsed mid-sentence?)  One guy mentioned an athletic 50-year-old pal who suffers from a heart issue like what’s described in the article.  Other responses:  “I have to admit, this article gave me pause, especially the way I like to ride bikes ... hung over, and hammering as hard as possible,” and “Alas, all along I thought I was doing something good for myself.”

Of course it’s tempting to deny the whole thing.  The article has some serious flaws—which I’ll get to in a minute—and I almost shrugged and thought, “Typical FUD, designed to sell magazines.”  But I resisted the urge.  After all, just because an article is flawed doesn’t mean its central assertion is false.  Besides, I respect the cautious position my pals have taken, and this isn’t the first time I’ve pondered the mystery of brilliant athletes suddenly dropping dead.  The article mentions two marathoners who died while running, and I also recall Matt Wilson, a local rider who died while cycling in 2011, and Steve Larsen, a guy I raced with as a junior, who died while running in 2009.

Never mind that my own heart has behaved perfectly my whole life (at least, as far as I know).  It’s possible I’m doing damage now that will only become a problem in ten years.  After all, I know guys who have smoked for years but don’t have lung cancer.  Yet.

I mulled over this article for about a week and a half, and just when it was starting to drift toward unconscious dismissal, I mentioned it to a cycling friend (my age) who said, “Oh, yeah, someone told me about that but said maybe I shouldn’t read it ‘cause it might bum me out.”  Why would it?  Turns out this guy has had a heart problem for some time now:  he’ll be riding along, just cruising, and suddenly his heart rate will go from like 140 up to over 200 and stay there for 30, 40 seconds.  Uh oh.

The “lumping” problem

My chief difficulty in deciding how much to worry, and whether or not to change my approach to cycling, is that of “lumping.”  Is it right to lump myself in with the guys cited in the article, and with the marathoners, and with Steve Larsen?  Is it right to lump runners in with cyclists?  And is it right to lump various heart problems together and treat them like one phenomenon?

Let’s take that last question first.  The Velo article uses two case studies to make its case:  Lennard Zinn, who while bicycling suffered symptoms of “his heart [flopping] like a fish” and beating way too fast; and Mike Endicott, who collapsed and lost consciousness during a cross-country ski race.  Was Endicott’s heart also racing?  Well, not at first.  Endicott’s words:  “Something was beating inside my chest.”  The Velo writer describes it as “his heart still doing something strange inside his chest” which led, after an hour or so, to ventricular tachycardia and “an immediate, unexpected loss of heart function.”  This seems a lot different from what Zinn experienced.  Were these two suffering from the same specific heart problem?  It’s not clear.

The article states that Zinn was diagnosed with multifocal atrial tachycardia, but Endicott’s exact diagnosis isn’t given.  The article talks a lot about atrial fibrillation (AF):  is this the same as tachycardia?  Again, it’s unclear (though this FAQ suggests not).  Moreover, the main study the article cites concerns “myocardial fibrosis, a condition that involves the impairment of the heart’s muscle cells, called myocytes, through hardening or scarring of tissue.”  Does myocardial fibrosis lead to tachycardia and/or fibrillation?  Do Zinn and Endicott suffer from myocardial fibrosis?  Once again, the article doesn’t say.

It’s not just this article that’s vague about this stuff.  I did a tiny bit of research on Steve Larsen’s death, and turned up something surprising:

Google’s big-font summary makes it pretty clear this was a heart attack—but it wasn’t, according to the first article cited.  Nothing else has been written to further clarify this matter; the autopsy itself apparently ruled out heart attack.  And yet people seem to remember it as such.  Two years after Larsen’s death, when I was corresponding with a friend about Matt Wilson, my friend wrote, “Steve Larsen was the guy who had a [fatal] heart attack two years ago here in Bend.”  Meanwhile, I’d always remembered Wilson’s death as having been from a heart attack, but in researching this now (for example, here), I can find no specific cause of death.

A dearth of data

Let’s get back to that Velo article.  My temptation, when presented with such ambiguity, is to read the research articles on which the article is based.  But the article, while making lots of vague references to unnamed studies, doesn’t provide much.  For example:  “Over decades of exertion, the myocardial cells of the heart begin to simply fall apart, and you’re left with an unhealthy ticker. Or so these new studies suggest.”  And:  “Long-term endurance exercise results in a five-fold increase in the risk of developing AF.  A review of the relevant research finds many small studies that correlate long-term sports activity with AF....  While none is conclusive, collectively they indicate a pattern.”  What studies?  What relevant research?  There are no citations given here; no footnotes; no hyperlinks.

The article does cite two specific studies.  One involved rats, and I’m going to dismiss that.  (My heart is bigger than a rat’s; rats don’t live 40 or 50 or 60 years, which is the age group I’m trying to learn about; humans cannot be made to exercise as hard as rats.)  Velo also cites a study published in The Journal of Applied Physiology:  “MRI studies revealed that some 50 percent of the veteran [>50-year-old] athletes had myocardial fibrosis....  In age-matched controls — people of the same age who didn’t compete — and young athletes, there were zero cases of the disease. Furthermore, the fibrosis was significantly associated with the number of years spent training, and the number of marathons and ultra-endurance marathons they had completed.”

Okay, now we’re getting somewhere!  I looked at the study itself to get more information.  You can read it here.  My big issue with this study is that it only included 12 veteran athletes.  Of these, 2 had previous heart conditions (1 probable previous mycarditis, 1 probable previous silent myocardial infarction).  The Journal study is candid about its limited scope, acknowledging that “Like many studies of this type, the numbers of veteran athletes are small (largely because this is a small and unique population), and generalization is difficult.”

And yet, without the ability to generalize, what are we supposed to do with this (largely anecdotal) information?  My frustration is that I feel I ought to evaluate and possibly modify my own behavior based on these cautionary tales, but I have no solid basis for assuming that my behavior matches the profile of the overworked athlete who may be damaging his heart.

Velo addresses this problem of definition by quoting Dr. John Mandrola, a heart rhythm doctor:  “What’s too much? That’s the $64,000 question. Though I will say it’s a little like what the judge said about indecency: ‘I know it when I see it.’”  Well, this just doesn’t do me much good, because I’m not about to go to Kentucky to visit this doctor, in the absence of any symptom of any problem.

I see four possible ways to respond to this information. 
  1. I could completely ignore it—but I think that’s irresponsible. 
  2. I could simply err on the side of caution, and ride less often and less hard than I currently do—but isn’t this completely arbitrary, since somebody who rides twice as much as I could similarly tone it down “a bit” and still be riding way more than I? 
  3. I could continue riding exactly how I currently do, while adding myocardial fibrosis to the pile of things I regularly worry about (which will increase my cortisol levels to the detriment of my health) while feeling guilty for being such a poor custodian of my body.  No thanks. 
  4. I can try to get more information about this, with a whole lot more data, so I can more reasonably evaluate and (if necessary) modify my behavior.
Number four wins, and that’s where my proposed solution comes in.

The solution

We need more information!  We need more than two anecdotes and a lot of vague references to “these new studies” and “the relevant research.”  We need more than studies on rats, and we need studies of more than 10 veteran athletes.  By “we” I mean “society,” and actually society is already really, really good at harnessing massive amounts of data and crunching them to derive useful judgments.  Think of how effectively Amazon predicts what we’ll want, and how well the advertising industry can anticipate, and create, our desires.  What if we could find a ready source of “big data” for studying the effect of gonzo endurance athleticism on heart health?

But we have it already!  It’s called Strava!  This social network has 8 million registered users, of which 1.2 million are active and something like 190,000 have premium accounts.  (These are estimations since the company doesn’t reveal these numbers; click here for details.  Suffice to say, this is a lot deeper pool of data than 10 test subjects.)

 The number of Strava users isn’t even the best part.  It’s the quality of the data set.  Consider the type of athlete who goes so hard, and so long, and so often, that he or she is actually at risk of causing heart damage.  How many of this type wouldn’t be on Strava?  The gung-ho Strava cyclist is exactly the kind of person who might overdo his or her training.  In other words, Strava members comprise the perfect group for studying this stuff. 

I’m envisioning a splash screen that pops up when the Strava user logs in.  It asks, “Are you willing to participate in an anonymous study about heart function and rigorous aerobic exercise?”  I’d guess most users wouldn’t have a problem with this.  And anybody who’s having heart trouble would probably be eager to participate, to better understand it all, and could indicate the nature and frequency of his or her problem.  Such a study could quite feasibly have millions of workouts per day to crunch (the average workouts logged per day being around 6 million last year, as detailed here).  You’ve got your control group and your heart-oddity group both covered, right off the bat.

And what great data there’d be to crunch!  You get exercise frequency; exercise duration; heart rate; and history (e.g., how much a rider’s performance is improving or deteriorating).  You could start to develop very precise profiles of those whose hearts are misbehaving.  Is there an age threshold beyond which these symptoms most commonly present?  Are there frequency, duration, and/or intensity thresholds below which no errant heart behaviors are observed?  What is the rate of heart trouble for riders exactly my age, who ride (on average) just as often, and in exactly the same heart rate zones I work out in?  Of those who work out like I do but who are 10 years older, how many have developed heart trouble?  Five years from now, when we see an even more comprehensive integration of “big data” into our lives, we’d probably have even more ways to correlate the data.  (We might know, for example, whether frequent purchases at Starbucks or BevMo factor in to the cardio health equation.)


For now, I’m going to assume that the hectic pace of my life, my many familial obligations, my relative sloth, and my unaggressive riding style will keep my heart in good shape.  I’m not going to bother shopping my Strava idea around, because I’m confident  that the Strava folks themselves, looking for a way to actually make some money, are bound to get the attention of the insurance people, who I assume are always looking for ways to avoid open-ended batteries of complicated tests.  I envision all of this happening without any effort from me, probably years before I start getting into the dangerous years where my heart starts “doing something strange inside [my] chest.”  And if you want to forward this link around to speed up the process, please be my guest!


  1. Rider dies at Leadville Trail 100 MTB race:

    1. I'm sorry to hear about that. Tragedies like this will continue to happen, just as people will continue to die, every day, in car crashes. The question is, are we comfortable--each of us--with the level of risk involved in the activities we do? Most of us do drive cars ... is that more or less risky than exercising really hard?

  2. The Strava idea is good, in terms of a large body of riders in the target range. But I don't think the most important thing would be captured, that being what kind of heart rhythm issue they might be experiencing. The data from a standard HR monitor is not going to show that. But it could be a great way to overlay exercise intensity/duration/frequency etc. with separately obtained health data - I'm thinking of e.g. annual echocardiogram data, EKG data, etc...

    1. Yes, the heart rate data in Strava is only a starting point. I think that, when trying to evaluate the cardiac risk of hardcore cycling, it'd be helpful to get some basic data on frequency of heart issues among ageing athletes, to bridge the gap between the anecdotal and the statistical....