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Marathons, heart damage, MRIs and VO2max

October 30th, 2010

The issue of heart damage in marathons has been a hot one lately, in the news most recently because of a study presented at the Canadian Cardiovascular Conference in Montreal last week. Laval University researchers did an MRI study of runners before and after a marathon, and concluded the less-fit runners sustain heart damage that can last for up to three months. They suggest that runners should get a VO2max test to determine whether they’re ready for a marathon.

Three points. First, do marathons “damage” hearts? This is the second MRI study to come out in the past year or so. The previous one, at last year’s Manitoba Marathon, found damage that disappeared within a week after the race. In the new study, they’re saying three months (note: since it’s just a conference presentation, I haven’t seen the details of the study yet). So it seems clear that marathon DO damage hearts — in the same way that they damage leg muscles, neuromuscular firing patterns, and probably even motivation to run, i.e. temporarily. As far as I know, there were no lasting negative outcomes in the Laval study.

Second, are runners who train less more susceptible to damage? This is the “novel” finding of this study, though it’s pretty obvious on an intuitive level. Personally, I think it’s a pretty good message: marathons are a big endeavour, and it’s worth training properly for them for all sorts of reasons. Do I think that those who persist in jumping into marathons with inadequate preparation are tempting fate? Not really — the statistics show that marathons as a mass participation event are still overwhelmingly safe compared to the baseline risk of other activities.

Third is this warning that prospective marathoners should get a VO2max test to figure out whether their heart can handle a marathon. I’ll have to wait until the full study is published to evaluate this more fully, but I’m a little skeptical. They initially point out that the heart is divided into 17 segments, and when one segment is injured/stressed the other segments can compensate, hiding the problem:

It also makes it practically impossible for physicians to arrive at an accurate assessment of the heart health of the marathoner when only considering the whole heart.

That’s why MRI is useful, because it can look at the segments individually. But then they turn around and suggest VO2max, which is an overall measure of cardiac function (not to mention all the controversies about what peripheral factors may also play into VO2max).

It just seems to me that VO2max is a pretty blunt instrument for figuring out who’s okay to run a marathon. It’s also a difficult, time-consuming and inconvenient test to run — so I’d like to see some assessment of what negative outcomes, exactly, we’d be hoping to avoid in exchange for the time and expense of hundreds and thousands of VO2max tests. Is it the handful of yearly deaths in major marathons (many of which would NOT be predicted by screening programs like this)? Or is it to prevent the temporary, invisible heart damage that marathoners have apparently been suffering with no ill effects for years?

  1. Brian
    October 31st, 2010 at 02:05 | #1

    Do they say anything about what the VO2max cutoff should be? Also, is the damage in ‘less trained’ runners independent of the length of time they actually spend running, or simply correlated to the length of time it takes them to complete the race?

  2. alex
    October 31st, 2010 at 02:43 | #2

    Great questions, Brian. I couldn’t find anything about what a suggested VO2max cutoff, but all I’ve seen is the press release and various media reports. It’ll be interesting to see what they say when the results are eventually published, but it’s hard for me to imagine they’ll have any credible basis for proposing a specific threshold unless their sample size is very, very large.

    And your second point is right on. Would we see the same results with, say, a three-hour time-trial? It’s reasonable to expect that less-trained runners (whose hearts are less adapted to the stresses) might still show more damage, but you’d certainly expect the trend to be less pronounced.

    Overall, I think these are useful studies to figure out how the human body responds to physical stress, but I think the attempt to put a “public health” spin on them is misguided. There’s certainly nothing here that convinces me that NOT running a marathon is healthier than running one, even with less-than-perfect preparation.

  3. October 31st, 2010 at 17:25 | #3

    This makes me think that the temporary heart damage is just like the muscular damage you get from the race. It’s temporary and is part of your body adjusting to the workload. Is the heart stronger after the 3 months of recovery? That would be an interesting follow-up question.

  4. alex
    October 31st, 2010 at 22:28 | #4

    Jason, I think you’re bang on that the temporary heart damage is just like the temporary muscle damage you get from racing a marathon.

    But that doesn’t mean you end up stronger three months later. To get stronger, you need a balance of stress, recovery, and adaptation. You do damage, it grows back stronger, then you repeat. For both the muscles and the heart, a marathon is too much stress — it does damage that forces you to spend at least a week or two, often more, recovering. By the time you’re done recovering, you’re probably a little weaker than you were before you started.

    To paraphrase Once a Runner, training is an act of creation, racing is an act of destruction.

    But then again, people don’t race a marathon to get stronger. They train to get stronger, then they race for the challenge. And as long as any damage done during the race is temporary, that’s no problem.

  5. Seth Leon
    November 1st, 2010 at 20:20 | #5

    The Vo2 max recommendation seems quite curious.

    You could do alot of speed training & shorter distances and be fit for say a 5k with a solid vo2 max but be way under-trained for a marathon. Vo2 max then wouldn’t be a good indicator of marathon preparedness.

    I think a good non-invasive post-race indicator of heart health recovery would be post race heart rate variability (HRV) compared to pre race levels.

  6. alex
    November 1st, 2010 at 22:55 | #6

    I agree, Seth. There are so many variables to consider with VO2max — is someone with a naturally high VO2max who hasn’t trained at all really better prepared than someone with a naturally low value who has trained diligently without significantly raising their VO2max?

    HRV certainly seems like a better metric, though it would be interesting to see studies. More fundamentally, though, I’m still not sure we NEED to have some threshold measure of whose hearts are best prepared for a marathon. Of course we all know that it’s better and healthier to be well trained before running a marathon. But I still haven’t seen any evidence that this temporary, invisible heart damage the researchers are talking about has any negative impacts. Maybe this damage is correlated to the extremely low risk of dropping dead during a marathon, but I don’t think that’s been demonstrated (those deaths are more usually assumed to be a function some underlying abnormality, not lack of fitness — hence Ryan Shay and Danny Kassap).

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