These men and women returned to the lab for new tests of their aerobic fitness and metabolic health. They also completed questionnaires about their current medical condition and medications and how often they exercised each week.

Then the researchers started comparing results and found telling differences.

Most of the men and women from the control group, who had not exercised 10 years before, had larger waistlines now, while the exercisers displayed little if any middle-aged spread compared to their decade-earlier selves.

Those from the control group also were less fit now. Most had lost about 10 percent of their aerobic capacity, which is typical of the declines seen after about age 40, when most of us will lose about 1 percent of our fitness annually.

But those men and women who had exercised vigorously for eight months during Strride retained substantially more fitness. On average, their aerobic capacity had fallen by only about 5 percent, compared to when they had joined the Strride study, and those few who reported still exercising at least four times a week were more fit now than they had been a decade before.

Interestingly, those Strride volunteers who had walked — meaning their exercise had been moderate, not intense — did not seem to have enjoyed the same lasting fitness benefits as those who had exercised more vigorously. Most of them had shed about 10 percent of their aerobic capacity during the past decade, much like the controls.

On the other hand, they showed surprisingly persistent improvements in their metabolic health, more so than among the intense exercisers. The walkers from 10 years ago still had healthier blood pressures and insulin sensitivity than they had had before joining Strride, even if they rarely exercised now. They had also had relatively healthier metabolisms than the men and women who had exercised intensely all those years before.

Taken as a whole, these results suggest that “exercise is a powerful modulator of health, and some effects can be quite enduring,” says William Kraus, a professor of medicine and cardiology at Duke, who oversaw the new study.