To 63-year-old Greg Cooke, seeing Diana Nyad this month become the first person to complete a 110-mile swim from Cuba to Florida was nothing short of awesome. Nyad is, after all, just a year older than Cooke, and she reminded him of what is possible.
"I saw that and I thought, 'Man, this is a total inspiration,'" he said. "It made me feel like I need to get up and get out there and do stuff."
Unlike Nyad, Cooke, a government attorney who lives in Garrett Park, Md., was not much of an athlete for most of his adult life. But when he was 48, he changed his ways.
"I had little kids and I was fat," he said. "I had a 6-year-old and I didn't want to be an old slug dad who couldn't keep up with the kids."
Cooke began running and now completes marathons, with finish times in the 31/2-hour range.
Most people are less physically active as they age. Only 1 in 5 American adults overall exercises enough, as defined by guidelines established by the U.S. Department of Health: at least 150 minutes per week of moderate aerobic activity, plus muscle-building activity at least twice a week. By their mid-50s, it is about 1 in 6; after 65 it's only 1 in 7, according to a study by the Centers for Disease Control and Prevention.
But while only a small share of people are exercising enough, the percentage of those exercising after age 65 has been rising.
As recently as 1998, only 6 percent of Americans over 65 routinely exercised up to federal levels, according to the CDC. Over the next decade, it doubled. In the most recent study, done in 2011, 16 percent got enough exercise.
The upswing marks a change in attitude since the middle of the century. In 1954, Jack LaLanne, a fitness and nutrition buff who had an exercise program on television, marked his 40th birthday by swimming the length of the Golden Gate bridge, underwater, carrying 140 pounds of equipment.
He did it to prove a point, said his widow, Elaine. "In those days, people thought anyone over 40 was over the hill."
Recent research suggests that this is far from the case. A 2010 study of muscle tissue from lifelong competitive runners in their 60s showed their leg muscles had almost as many motor units, a measure of strength, as those of active 25-year-olds.
But starting exercise regimens at any age can be beneficial, according to the National Institute on Aging, which runs a website to encourage exercise among older people (go4life.nia.nih.gov/).
Nyad's accomplishment shows that state of mind can be as important as physical prowess, say experts on the physiology of aging.
"It's more a testament to her spirit than her body," said Gayle Doll, director of Kansas State University's Center on Aging. "She is relentless. Diana Nyad's message is, you can do incredible things when you're older. We've just been told that we can't. A lot of people have the body to do it, but they don't have her indomitable spirit."
The human body loses protein with age, and with it goes muscle mass. In so-called power sports, such as gymnastics or the 100-meter sprint, people hit their peak in their 20s. But in endurance sports like swimming or long-distance cycling, athletes don't peak until their 30s, after many years of training.
"Every time we say there are limits to the human body, someone like Diana Nyad breaks it," said Frank Wyatt, who teaches exercise physiology at Midwestern State University in Texas. "In most studies on aging, the line goes in one direction, and it's generally down. Not a lot gets better. But if you look at Diana Nyad, you can say maybe our resolve does."
Doll said women often are better at endurance sports than men are because their bodies have more fat, which helps fuel their activity.
"You have to work harder, but you can maintain a lot of muscle mass," said Doll, citing a study in the 1990s in which nursing home residents who did quadriceps training almost tripled their strength.
Carol Mackela, 62, of Arlington, Va., was a competitive diver in college but didn't dive for 33 years until 2006, when she heard an old teammate from college was still doing it. "Her dives looked better than in college," she said.
Looking around in the local area, she initially had a hard time finding a coach who would take her on. One coach "didn't have time for adults; he wanted to fill his slots with kids who are going to the Olympics," she said.