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The debate about whether “extreme” exertions like running a marathon can damage your heart continues to simmer. The latest addition is a paper published online last week in Medicine & Science in Sports & Exercise by a group from TU Munich. One of the co-authors is Stefan Moehlenkamp, whose recent studies of fibrosis in the hearts of veteran marathon runners have stirred up controversy.
In this study, they took blood tests (and various other measurements) from 102 participants in the Munich Marathon, before, immediately after, 24 hours, and 72 hours after the race. They were looking at the rise and fall of various “cardiac biomarkers” that signal possible heart damage, in particular and newly developed test for cardiac troponins that is much more sensitive than previous tests.
We already know that troponin levels rise after a marathon — but we don’t whether that’s a signal that heart muscle cells are dying, or whether it just signals some temporary damage, in the same way that your leg muscles are temporarily “damaged” by a marathon but quickly recover. When heart muscle cells actually die, as in a heart attack, levels of troponin stay elevated for four to seven days, as troponin continues to leak from the dead cells. In contrast, temporary damage causes a sharp peak in troponin that returns to normal after a few days. Here are the results:
Combining this sharp peak and quick decline with the other measurements in the study, the researchers conclude that “cardiac necrosis [i.e. cell death] during marathon running seems very unlikely.” Instead, the evidence points to temporary damage to cell membranes, possibly caused by decreased availability of oxygen or ATP during the race.
Referring to the earlier study that found fibrosis in veteran marathon runners, the researchers write:
Findings of myocardial injury, as seen in older marathon runners (5) are probably independent of marathon running but rather related to cardiovascular disease or risk factors, particularly smoking.
Does this mean the controversy is over? Far from it. For one thing, this study was written before more recent results showed possible heart damage in elite athletes who weren’t former smokers. More research, as always, is needed. But the results are encouraging — I remain pretty firmly convinced that the cardiac benefits of training for and competing in marathons dramatically outweigh the putative risks.