The 64-year-old Nyad plans to swim for 48 hours straight next month, accompanied by celebrities swimming laps alongside her, in a specially designed swimming pool that will be erected in New York City to raise money for Hurricane Sandy survivors.
Although the swimmer insists she isn't trying to prove anything — "I didn't do this because I was in my 60s. I just happened to be in my 60s," she says — she acknowledges that her success is having an impact, "not just on people of my generation but on younger people."
"I have a godson who's 14 and he texted me yesterday and said, 'I'm never in my life again going to call someone in their 60s old. It's over. You just proved that youth doesn't have anything to do with age.'"
And at one point during an interview Tuesday with The Associated Press, the bronzed, muscular athlete couldn't resist sharing a message of encouragement and solidarity with those of her generation:
"Baby Boomer power!" she declared, with a triumphant fist pump.
On her fifth try, Nyad finished the 110-mile swim from Havana to Key West on Monday in 53 hours, becoming the first to do it without a shark cage. She said that while she is slower than she was back in her 20s when she first gained national attention for swimming around Manhattan and from the Bahamas to Florida, she feels she is actually stronger.
"Now I'm more like a Clydesdale: I'm a little thicker and stronger — literally stronger, I can lift more weights," Nyad told the AP.
"I feel like I could walk through a brick wall. ... I think I'm truly dead centre in the prime of my life at 64."
Nyad isn't alone among aging athletes who are dominating their sports.
Earlier this year, 48-year-old Bernard Hopkins became the oldest boxer to win a major title, scoring a 12-round unanimous decision over Tavoris Cloud to claim the IBF light heavyweight championship.
Tennis player Martina Navratilova won a mixed doubles title at the U.S. Open in 2006, just before turning 50, and decades ago hockey legend Gordie Howe played professional hockey into his early 50s. Golfer Tom Watson was nearly 60 when he fell just short of winning the British Open in 2009. Last year, baseball's Jamie Moyer was 49 when he became the oldest starting pitcher to record a major-league win.
Thousands of U.S. athletes, including 60-year-old Kay Glynn, also compete during the Senior Olympics.
Glynn, of Hastings, Iowa, has won six gold medals in pole vaulting at the Senior Olympics and set a new pole vaulting world record for her age in the 2011 National Senior Games.
Older athletes tend to find more success in endurance events than in power events such as sprinting and other sports that rely on "fast- twitch" muscle fibers, which are more difficult to preserve later in life, noted Wojtek Chodzko-Zajko, a physiologist at the University of Illinois Urbana-Champaign.
But just because Nyad was swimming rather than pounding her joints against the concrete doesn't mean she didn't achieve a remarkable feat, Chodzko-Zajko said.
"This ultra, super-length swimming is brutal regardless," he said, adding that another reason athletes are able to endure is because they often train smarter and have a mental concentration that is well-honed over decades.
"She's one of any number of people who are redefining what happens with aging," said Dr. Michael J. Joyner, an anesthesiologist and exercise researcher at The Mayo Clinic.
"If you start with a high capacity, you have some reserves," Joyner said. "You can lose some absolute power, but what you lose in power you can make up for with experience and strategy and better preparation."
Nyad first attempted swimming from Cuba to Florida at age 29 with a shark cage. She didn't try again until 2011 when she was 61.
She tried twice more in the past two years before beginning her fifth attempt Saturday morning with a leap off the seawall of the Hemingway Marina into the warm waters off Havana. She paused occasionally for nourishment, but never left the water until she reached the white sand beaches of the Keys and waded ashore.
Nyad says her age and maturity should not be discounted when measuring her most recent success.
"It's not so much the physical," she said. "To my mind all of us ... we mature emotionally ... and we get stronger mentally because we have a perspective on what this life is all about," Nyad said.
"It's more emotional. I feel calmer, I feel that the world isn't going to end if I don't make it. And I'm not so ego-involved: 'What are people going to think of me?'" I'm really focused on why I want to do it."
Australian Susie Maroney successfully swam the Straits in 1997 at age 22 with a shark cage, which besides providing protection from the predators, has a drafting effect that pulls a swimmer along.
In 2012, 49-year-old Australian Penny Palfrey swam 79 miles toward Florida without a cage before strong currents forced her to stop. This June, Palfrey's countrywoman Chloe McCardel, 28, made it 11 hours and 14 miles before jellyfish stings ended her bid.
Nyad acknowledged Tuesday that she was glad when McCardel didn't make it before she had a chance to, but she did add, to laughter from her team, "I didn't want her to get bitten by jellyfish or die or anything."
Associated Press Writer Kelli Kennedy in Miami contributed to this report.
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