These soon-to-be marathoners agreed to visit the university’s lab, completing health and fitness tests and a sophisticated scan of their aorta, designed to measure its flexibility. None of the group showed signs of heart disease or other serious health problems.

Each runner then began his or her preferred marathon-training program, with most jogging a few times a week. This training continued for six months, although some developed injuries or other concerns and dropped out. Ultimately, 136 men and women completed the race, in an average finishing time of 4.5 hours for the men and 5.5 hours for the women. A week or two later, they returned to the lab to repeat the tests.

Their aortas proved to be more flexible now. In fact, their arteries seemed to have shed the equivalent of about four years, in functional terms. The aorta of a 60-year-old marathoner in the study now expanded and contracted about as lithely as that of a 56-year-old participant did at the study’s start, and the 56-year-old’s arteries worked like those of a pre-race 52-year-old, and so on.

These improvements were most marked in older male runners and those whose finishing times had been slowest. They did not depend on changes in runners’ fitness or weight, which, in most cases, had been negligible. All that had mattered was that people had kept up with their training and raced.

These findings gratified the researchers, says Dr. Charlotte Manisty, a consulting cardiologist at University College London and the Barts Heart Center, who oversaw the new study. “We had not really known” whether the arteries of sedentary people “could or would benefit” from exercise training, she says, especially if the people were older or notably out of shape. “We just didn’t know how much plasticity their arteries still had.”

The answer seems to have been plenty, however, she says. “Almost everyone benefited,” she says, “and those people whose arteries needed the most help benefited the most.”

But these results do not consider the large number of would-be marathon racers in the study who did not make it to the start line. It is also unknown whether the rejuvenation of runners’ aortas is likely to last or if the benefits will be lost if they do not continue to run.