When it comes to athletic prowess, Sheila Lurie Isaacs admits she was a late bloomer. Growing up in Johannesburg, South Africa, she says she was about as nonathletic as a child could be.

But Google search “Sheila Isaacs triathlete” today and up pop formidable rankings in triathlon results. That includes a first-place finish in her age group at the 2015 USA Triathlon Sprint National Championships held in Milwaukee last August.

At age 78, the Shoreham resident and grandmother of two teenage girls, is at the top of her athletic game — a lifetime away from her early years. “I was the total nerd,” she says of her school days. “Tennis and swimming were compulsory. And I hated it.”

That distaste for exercise stayed with her until she hit 50. For that special birthday, her daughter, Claire, bought her a gift that altered her attitude. “It was a pink girl’s bicycle,” embellished with purple tassels and a plastic basket with flowers, recalls Isaacs, who also has a son, Darryl. So she started biking.

One day, a colleague at what was then the Long Island Lighting Co. goaded her about entering a triathlon, an event that includes bicycling, swimming and distance running. Isaacs says she always welcomed a dare, and after hearing the run was only 3 miles, she signed up. “I can always walk it if I got tired, I thought. Right?” She later learned the run was 6 miles but she didn’t back out. Isaacs already knew how to swim and was comfortable on her bicycle, so she thought, why not?

She was 53 when she ran that first triathlon in Montauk. “I never ran before,” she says, “but I did it. I got a medal and a T-shirt. It was fun.” And she has been competing ever since. Twenty-five years later, she has close to 200 triathlons under her swim cap and has finished all but two of them: one because of a flat bicycle tire, the other due to a leg cramp while swimming.

Older athletes like Isaacs who push themselves to compete in triathlons are still very much in the minority when compared with younger generations, experts say. The list of those running well into their 80s (and a few in their 90s) is growing, but it’s still not a crowded field, says Lindsay Wyskowski, spokeswoman for USA Triathlon. While triathlons may seem more challenging for older athletes, Wyskowski says, “It’s an activity that you can do at any age. They can find something to meet their ability level and interests.”

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Isaacs participated in triathlons, half-marathons and even an Ironman competition, which includes a full 26.2-mile marathon component, until she was in her 60s, Now, she mostly competes in shorter events known as sprint triathlons, usually made up of a 750-meter (almost half-mile) swim; 20-kilometer (12-mile) bicycle ride; and a 5K (3.1-mile) run. At her age, she says, it’s more about finishing the race and enjoying new places to compete than winning.

Her later-in-life passion for these races has taken her from New Zealand to Israel, Argentina to Canada. She won first place for her age group at the 2014 International Triathlon Union World Championship in Edmonton, Canada, a race for athletes who must qualify by times logged at the USA Triathlon Sprint National Championships, where Isaacs has placed first for the past two years in the female 75-79 age group. For the international event, Isaacs was part of the U.S. team of women in her age group.

Years of competition have also taken her to all 50 states. The last one was Hawaii in 2004 for the Ironman World Championship in Kona, which marked her 100th triathlon. Remarkably, Isaacs, who was 67, won a silver medal in her group of six competitors despite falling and breaking her pinkie during the event. She barely made it to the finish line to beat the 17-hour cutoff. With the Kona results in, news reports stated that Isaacs was the first known athlete to complete a triathlon in all 50 states.

Isaacs plans to run in USA Triathlon’s National Sprint Championship in Omaha, Nebraska, in August and the International Triathlon Union World Cup in Cozumel, Mexico, in September. She is also looking forward to the 2017 World Cup at Rotterdam, Holland, if she qualifies — and she hasn’t missed the starter’s gun yet.

No matter the season, Isaacs is serious about training. If the weather is not too cold or dangerous, she bicycles at local parks and on bike trails; the pink bicycle has been replaced with a high-performance one. She runs 3 or 4 miles twice a week; once a week she takes a 6-mile run, often with her husband, Hugh Isaacs, 79, a retired Brookhaven National Laboratory electrochemist. She loves to run outside, usually at a nearby high school. “I do speed work on the track,” she says. “If you want to call it that. Speed for me ... but I pace myself the best I can.” If they need to head indoors, they go to Planet Fitness in Rocky Point.

As long as the water isn’t too frigid, she swims in Long Island Sound near her home at least three times a week. But in winter, she trains at the Town of Brookhaven Aquatic Center in Mastic Beach. She swims for 90 minutes in the heated pool twice a week, stopping only to check her stroke chart to keep on schedule. She alternates strokes, later switching to fins to work out her legs. She lifts weights, does yoga and every day tries to do back-to-back workouts that engage two elements of the triathlon.

Isaacs keeps copious spreadsheets for her workouts, and logs in every race, with times, wins, number of competitors, photographs and other pertinent information. “I’m a statistics person,” she says.

Her dedication to training draws admiration at the pool. Frank Luberto, 64, of Ridge, calls her incredible. “It’s never too late,” says Luberto, who is also a runner. “She raised her children, and now she has the time.”

Wading River resident Barry Naber, a runner who recently started swimming at the aquatic center, says Isaacs is an inspiration. “I just learned to swim,” says Naber, 67. “She gives me good advice.”

Many times, the competitions take Isaacs, a retired computer systems analyst, and her husband to places they may not otherwise have visited. Once the couple toured Wyoming, North Dakota, South Dakota and Idaho so she could compete on four consecutive weekends, while stretching to complete their 50-state goal. “We rented a car, and went to many of the state parks,” she says. “The motivation is to travel. The excuse is to find a triathlon there.”

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Isaacs, who has lived in the United States for nearly 50 years, competes in regular races as well. Last month, she took first place in her age group at the New York State Parks Winter Run Series, 5-kilometer race events that are held on weekends.

One place she has not yet run is in her South African homeland. She plans to compete there eventually, when the race coincides with visiting family and friends. “It’s time,” she says.

Her avocation of triathlon racing is now more a marathon than a sprint, she says. Isaacs notes that over the years, a sprint triathlon that once took her 90 minutes now takes more than two hours. But that’s not a deterrent. “I’ve no physical reason to stop,” she says. “My knees are good; my physical energy is fine ... and I’m very aware of protecting myself. I want to keep doing this.”