rom exercise, analysed changes to the heart and blood vessels that are sometimes found in endurance athletes.
The Mayo Clinic scientists found occurrences of irregular heartbeats, enlarged hearts and thickened artery walls, but it was unclear how many, if any, of those effects were potentially harmful or whether they were pre-existing conditions. And it was also not known how many endurance athletes actually experience those effects.
"Any blanket statement about these runners is sure to have exceptions to it," said Dr James Fries, a professor of immunology and rheumatology at Stanford who has studied runners for decades. "We study the mean, and we report what happens to this group or that group. But nobody's actually the average."