The Ironman World Championship in Kona, Hawaii, is considered one of the toughest one-day endurance events on the planet. Among the finishers in this year’s Oct. 8 race was Barbara Cronin-Stagnari, a determined 55-year-old mom from Mineola.

It was Cronin-Stagnari’s sixth time competing in the Kona triathlon, and her 18th Ironman-distance triathlon overall. She completed the course — a 2.4-mile swim, a 112-mile bike ride and a 26.2-mile run through torrid lava fields — in 12 hours, 14 minutes, 19 seconds, coming in 1,645 in a field of about 2,300 athletes; she placed 11th in her age group.

“It was not quite the race I wanted,” said Cronin-Stagnari, who became dehydrated and struggled through the last nine miles of the run. She was, however, pleased that she was first in her age group in the swim part of the triathlon (she earned a separate award for that) and had a solid bike leg. Still, she said, the highlight of the race came at the end. “Having my four kids and my husband at the finish line was the best!”

Even in Kona, which attracts many of the world’s best competitors, Cronin-Stagnari’s credentials are formidable. According to race organizers, only 51 of this year’s large field of athletes have more career Ironman finishes than her.

It is, many say, the ultimate endurance test, requiring months of discipline and intensive workouts. “Most of all, it’s fun,” Cronin-Stagnari said. “I love the training and the competition. And I always think I can do better.”

For this year’s Kona championships, her training averaged 15-18 hours a week. The regimen included 100-mile bike rides on the North Shore; 20-mile training runs at SUNY Old Westbury; crack-of-dawn track workouts at The Wheatley School, also in Old Westbury; and swims at the Nassau County Aquatic Center in East Meadow.

Most of the time, Cronin-Stagnari manages to surround herself with training partners. “I always try to have some company,” she said. On the mornings she rides or runs alone, music is her sidekick. “I’m a Deadhead, a Parrothead, a you-name-it head,” she said, laughing, referring to the names used by fans of the Grateful Dead and Jimmy Buffett. “I’m a huge classic rock fan.”

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She also takes time to visualize the famously brutal Kona course, known for its searing winds and lava fields. “I equate it to riding into a giant hair dryer,” she said. NBC-TV is scheduled to air the race Dec. 10 at 2:30 p.m.

One reason Cronin-Stagnari is able to train and compete at such extreme distances and in extreme conditions is simple, said an expert who knows her: She’s built for it. Her 5-4, 118-pound frame absorbs the training without getting injured. “She is without a doubt an endurance machine,” said triathlon coach Jose L. Lopez of Mineola, her longtime mentor and friend. “She doesn’t break down, and she’s able to accommodate a tremendous volume on a daily basis. That’s the recipe for success in the Ironman.”

It was Lopez who persuaded Cronin-Stagnari, in 2006, to attempt her first Ironman in upstate Lake Placid. But it was her mom, Kathy Cronin, who first nudged her to put her toe in the water — literally.

“She said it was something you could do your whole life,” Cronin-Stagnari said. “She was right.”

Cronin-Stagnari swam competitively at SUNY Buffalo State, where she majored in special education. She worked summers as a lifeguard at Rockaway Beach, where one of the first triathlons she competed in was held in 1983. That initial outing included a mile swim, 25-mile bike ride and 13-mile run. “I’d never run more than three or four miles,” she said. Egged on by fellow lifeguards, she completed the race. (She still has the T-shirt.) She continued to do shorter-distance triathlons as they began to pop up locally in the 1980s.

In 1989, she married Jack Stagnari, a New York City firefighter. The couple had four kids in 5½ years and she kept on training. Sean is now 26; Danny, 24; Jackie, 22; and Katie, 20.

“Some of my earliest memories are sitting in that baby jogger she used to have,” recalled Jackie Stagnari, now a senior at Northeastern University in Boston.

Cronin-Stagnari juggled the responsibilities of parenting with her drive to train in long-distances. “I used to bike to SUNY Old Westbury, do a workout there, come home, eat a bowl of cereal, put the kids on the bus, and then go back out and ride some more,” she recalled. Her training and competing took off once she found Ironman competitions, and she continues to participate in shorter triathlons. In between, she has run 35 marathons and six ultras, defined as races longer than 26.2 miles. “I love to race,” she said. “I would do it every weekend, if I could.”

During the last weekend of July this summer, Cronin-Stagnari may have had the race of her life. In the same Lake Placid Ironman where she made her debut 11 years earlier, she won her 55-59 age group by a remarkable margin of one hour. She finished ahead of 34 women in her age group, completing the course in 12 hours, 7 minutes.

“That was pure domination,” said Lopez of his former student. “She had the fastest swim, fastest bike, fastest run in her age group. That’s very unusual.” (By comparison, the overall female winner of Ironman Lake Placid went the distance in 10 hours, 13 minutes.)

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By virtue of her Lake Placid performance, Cronin-Stagnari qualified for the world championship in Kona.

Like most Ironman athletes, Cronin-Stagnari, who has been coaching other triathletes since 2003, is dedicated to her training, but she also has a lighthearted approach. “She’s the person in a sports bra running in 20 degrees,” said Dave DiGiovanni, 58, a Sea Cliff architect who was coached through his first Ironman by Cronin-Stagnari. “She is tough, absolutely, but she really enjoys it.”

The memory of her father, William Cronin, helps motivate her. “He was 43 when he died and I was 12,” she said. “He didn’t get a chance to do a lot.” It’s one reason she tries to enjoy her training and encourages the athletes she coaches to approach the sport with a similar attitude. “When I coach people, I say, ‘Did you have fun today? Did you feel good about what you did in this race or that training session?’ That’s the important thing.”

Her daughter Katie used to roll her eyes at Cronin-Stagnari’s exuberance. “When we were young, we were embarrassed,” she said, “but now it’s kind of cool that she’s in such great shape for her age.”

Cronin-Stagnari said there’s another payoff to all of her training. “A lot of times, I’ll be racing, thinking, ‘Man, I could be home cleaning the house.’ Not a lot of women my age get to do this,” she said, “I’m so lucky.”