Marathons may harm the heart, in the long run

Small study raises questions over biomarkers in runners. Nick Carne reports.

Runners warming up for a marathon.

Runners warming up for a marathon.

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Whether amateur athletes should run marathons is a topic of great debate. Some say it is ideal exercise if you’ve trained for it, and others that 42 kilometres is just too far to be safe or sensible.

A new Spanish study adds a little extra weight to the latter argument.

Researchers from Camilo José Cela University in Madrid have found that completing a full marathon puts greater strain on a runner’s myocardium – the muscular tissue of the heart – than tackling a half marathon or a 10-kilometre run.

That may seem obvious, but the key point is that all the runners trained appropriately for the distance they chose to run, and their self-reported perceived exertion rates were similar.

Marathoners felt just as comfortable with what they had done as those who covered significantly shorter distances, yet a study of cardiac biomarkers showed the effort had put much greater strain on their hearts.

The findings of the study, which was led by the director of the University’s Exercise Physiology Laboratory, Juan Del Coso, are reported in a paper published in the journal Circulation.

The researchers stress that the sample size of 63 – comprising 21 runners covering each of the three distances – was too small to accurately assess differences in 10-year cardiovascular risk, and that more work is needed to get a clearer picture. But the early results are there to see in the measured concentrations of proteins called troponins, which are present in heart tissue.

“Although the release of cardiac troponins after the exercise may not be indicative of any cardiovascular dysfunction, the higher concentration of cardiac troponins after the marathon reflects a superior cardiac stress at this running distance,” they write.

“The greater cardiac stress after the marathon was present despite a higher training volume.”

The incidence of cardiac arrests in marathoners is only around one in 100,000 finishers, but a high proportion of all exercise-induced cardiac events occurs during marathon competitions, particularly in males aged over 35.

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