George Sperzel, 63, estimates that he’s run over a hundred competitive races over the last few years.

Sperzel, a finance executive from Lake Forest, Illinois, dabbled with exercise in his younger years, but didn’t embrace competitive running until he was nearly 60. Despite his late start, though, he feels that his athletic ability has only gotten better with time: “I have found that focused training will deliver the same benefits for aging athletes as for anyone of any age,” he says.

In general, peaking in one’s 60s is somewhat of a rarity. In sports medicine, the years between 35 and 40 are often considered a turning point for serious athletes: Skill begins to erode more quickly with time as age brings changes in muscular strength and susceptibility to injury. Endurance tends to peak around age 35 and then slowly decrease until around age 60, at which point the decline becomes much steeper. And unsurprisingly, it holds true across generations that older adults as a group tend to be less active than their younger peers. Roughly one-third of Americans over the age of 65 are considered physically active, compared to around 80 percent of the general population.

But within the minority of active seniors, some, like Sperzel, have held on to or even increased their athleticism. In recent years, a growing number of senior citizens have begun competing in marathons and triathlons, causing experts to question much of the conventional wisdom about age-related changes in physical capacity. In U.S. marathons, runners over the age of 40—known as “masters” in the running world—now represent more than 50 percent of male finishers and 40 percent of female finishers, often outperforming younger athletes.  

Greg McMillan, the owner and head coach of McMillan Running, an online company that coaches competitive runners, says he’s worked with many older athletes, a large number of whom only recently took up the sport. “We’ve never had so many people starting to get active later in life and stay active through their advancing years,” he says. “So we can no longer lump everyone in the same boat because of age.”

“In the past, the majority of finishers in marathon and triathlon races were young competitors,” agrees Hirofumi Tanaka, an aging researcher and a professor of exercise science at the University of Texas. “The demographics of participants have shifted substantially.”

These older runners may be reaping rewards beyond a medal at the finish line: Research has shown that exercise can help maintain physical fitness that may otherwise be lost over time. "A lot of the deterioration we see with aging can be attributed to a more sedentary lifestyle instead of aging itself,” a 2014 review article on aging and exercise, published in the Journal of the American Academy of Orthopedic Surgeons, concludes. “The prevalence of age-related chronic diseases and physical dysfunction is substantially reduced or even absent in older adults who continue to train and compete in athletic competitions."

“Aging merely lowers the ceiling of physical ability,” Tanaka says. "Older adults, even those over 90 years of age, respond well to exercise training and regain much of what they lost with aging.”

But the authors of the 2014 study emphasize that athletic feats like marathons aren’t the only way to enjoy the benefits of exercise in old age. According to their data, any regular vigorous exercise may reduce the decline in aerobic capacity—the ability of the heart and lungs to deliver oxygen to muscles, a main component in overall age-related physical decline—by as much as 50 percent.

According to a 2011 study published in the journal The Physician and Sports Medicine, muscle strength can also be preserved through exercise. While some loss of strength is inevitable, the researchers found that older athletes who participated in exercise programs showed significantly more muscle strength that people of similar age who didn’t exercise. Maintaining muscle strength can be a key component of successful aging, as past research has shown that its loss in seniors is correlated to an increased risk of falling, a significant cause of age-related trauma.

In fact, contrary to popular belief, older adults are not at an overall increased risk of injury when participating in exercise activity; rather, regular exercise puts them at diminished risk compared to their sedentary peers. The 2014 study noted that regular movement can strengthen bone density, which protects against osteoporosis, while a separate study, published in 1985 in the Journal of Applied Physiology, found that it can also help reduce the risk of arthritis and injuries to tendons and ligaments.

Even for the adults who haven’t exercised in years or even decades, research suggests that late is still better than never. A 2014 study in the British Journal of Sports Medicine found that among a group of people aged 55 to 73, those who had exercised at least once a week subsequently had lower rates of chronic disease, depression, and “physical or cognitive impairment” than their more sedentary peers. However, the subjects that began the study as sedentary but began exercising regularly sometime over its eight-year follow-up period had outcomes that were almost as good.

For optimal results across the board, researchers say, older adults should routinely strive to exceed the minimum weekly exercise recommendations for their age group: 150 minutes of week of moderate-intensity activity or 75 minutes of vigorous activity, and two sessions of muscle-strengthening exercise, according to the Department of Health and Human Services. But the advice comes with a caveat: Gains in fitness, function, and health are reliant on the maintenance of an exercise program. If a person stops exercising, the effects can be reversed in a relatively short amount of time.

It’s an unavoidable truth that physical function does diminish with age, and exercise cannot fully protect against the natural aging process. What it can do, however, is reduce the magnitude of this decline. By staying active and competitive, older athletes may help more sedentary seniors realize that an active lifestyle may lead to not only longer life, but a better life, too.

Sperzel, for one, has no intention of slowing down in the years ahead. “I am literally in the best shape of my life,” he says, “and physically I feel better than I ever have.”