The muscles of older men and women who have exercised for decades are indistinguishable in many ways from those of healthy 25-year-olds, said an uplifting study of active septuagenarians.

These men and women also had much higher aerobic capacities than most people their age, the study showed, making them biologically about 30 years younger than their chronological ages, the study’s authors concluded.

All of us are aging every second, of course, which leads many of us also to be deeply interested in what we can expect from our bodies and health as those seconds — and subsequent years and decades — mount. Worryingly, statistics and simple observation suggest that many elderly people experience frailty, illness and dependence.

But science has not established whether and to what extent such physical decline is inevitable with age or if it is at least partly a byproduct of our modern lifestyles and perhaps amenable to change.

There have been hints, though, that physical activity might alter how we age. Recent studies have found that older athletes have healthier muscles, brains, immune systems and hearts than people of the same age who are sedentary.

But many of these studies have concentrated on competitive masters athletes, not people who exercise recreationally, and few have included many women.

So for the new study, which was published in the Journal of Applied Physiology, researchers at Ball State University decided to look at a distinctive set of older men and women.

“We were very interested in people who had started exercising during the running and exercise booms of the 1970s,” said Scott Trappe, director of the Human Performance Laboratory at Ball State.

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

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 said.

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

They recruited 28 of them, including seven women, who had been physically active for the past five decades. They also recruited a second group 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 measured the number of capillaries and levels of certain enzymes in the muscles. High numbers for each indicate muscular health. The young people, researchers thought, would possess the most robust muscles and aerobic capacities, with the lifelong exercisers being slightly weaker and the older nonexercisers punier still.

But that outcome is not precisely what they found.

Instead, the muscles of the older exercisers resembled those of the young people, with as many capillaries and enzymes as theirs, and far more than in the muscles of the sedentary elderly.

The active elderly group did have lower aerobic capacities than the young people, but their capacities were about 40 percent higher than those of their inactive peers.