That era, bookended to some extent by the passage of Title IX in 1972 and the publication of “The Complete Book of Running” in 1977, introduced a generation of young men and women to recreational physical activity, Dr. Trappe says.

“They took up exercise as a hobby,” he says.

Some of them then maintained that hobby throughout the next 50 or so years, running, cycling, swimming or otherwise working out often, even if they rarely or never competed, he says.

Those were the men and women, most now well into their 70s, he and his colleagues sought to study.

Using local advertisements and other recruitment methods, they found 28 of them, including seven women, each of whom had been physically active for the past five decades.

They also recruited a second group of age-matched older people who had not exercised during adulthood and a third group of active young people in their 20s.

They brought everyone into the lab, tested their aerobic capacities and, using tissue samples, measured the number of capillaries and levels of certain enzymes in the muscles. High numbers for each indicate muscular health.

The researchers focused on the cardiovascular system and muscles because they are believed inevitably to decline with age and the scientists had expected they would see what Dr. Trappe describes as a “hierarchical pattern” in differences between the groups.

The young people, they thought, would possess the most robust muscles and aerobic capacities, with the lifelong exercisers being slightly weaker on both counts and the older non-exercisers punier still.