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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?