For most of us, the idea of completing a 2.4-mile ocean swim, followed by a 112-mile bike ride through blazing-hot lava fields, then finally running a full marathon, sounds grueling.

But for 73-year-old Bobbe Greenberg, participating in the Ironman World Championship triathlon in Hawaii is a celebration.

“I am very, very, very lucky in my life,” said Greenberg, who lives in Highland Park, Ill., with her husband of 50 years.

While she’s arguably one of the fittest septuagenarians in the world, Greenberg’s greatest strength may actually be her mind.

On Saturday, the retired English teacher will return to the Ironman World Championship for the seventh time. This year, she’ll defend her title as the women’s age 70-74 champion.

Like most women of her generation, Greenberg didn’t grow up playing sports. She discovered her competitive streak during a mandatory fitness challenge, in which she set a record for knee raises in the fifth grade. She was the kid on the playground who always wanted to race or play tag.

Despite her athletic inclination, in high school she remained with the rest of the girls on the sidelines. As a cheerleader, she never imagined she’d someday become an athlete in her own right, let alone one of the best long-course triathletes in the world.

As a 22-year-old newlywed in 1968, Greenberg started playing in tennis tournaments, and her strong match performances showed her that she could persevere despite her lack of technique.

“I had no strong game. I had no backhand, no serve,” she said.

Instead, she outlasted opponents: “I just won by keeping the ball in play.”

Competing in triathlons wasn’t on Greenberg’s radar more than three decades later when she joined a gym in 2001. Her motivation at the time, she said, was she noticed she had “terrible posture.”

Her spin instructor announced an upcoming indoor triathlon and encouraged the class to participate. It consisted of a 10-minute pool swim, a 20-minute stationary bike ride and a 15-minute treadmill run. She was 57 at the time and thought, “Why not?”

There was only one problem.

Greenberg didn’t know how to swim.

Initially she thought she’d skip swimming and run back and forth across the pool since the water was only waist-deep.

“And then I thought, ‘That’s stupid,’ ” she said. “Why would I embarrass myself like that? I should learn how to swim.”

She took a weekend course to learn the basics. She considered it expensive but saw it as an investment in her future. “This is something I can do when I'm 90,” she recalled thinking.

Despite her rudimentary swim skills, Greenberg finished her debut triathlon that year in first place. She was 20 years older than the second-place woman.

She’s been hooked ever since. She trains at least 15 hours a week and participates in shorter races nearly every weekend in the spring and summer, when she’s not spending time with her four grandchildren. She estimates she’s completed 16 or 17 triathlons this year.

She loves the way racing makes her feel.

“It’s like a drug,” she said. “I’m sweating, and I’m pushing myself to my limits, and there’s something very exhilarating. I think it’s that feeling of youthfulness or vibrancy. … There’s something it gives to me that I’m not able to get in any other way in my life.”

Triathlon training also lets her be outdoors, which studies show promotes mental and physical well-being. She described “a feeling of spirituality, being outside, looking at nature.” Other competitors will complain about strong winds after a race. But Greenberg doesn’t even notice them. “I’m like, ‘Really?’ [I’m in] a positive state the whole time,” she said.

Focusing on the positive comes naturally to Greenberg. It’s something she picked up from her brother, who died a few years ago after living his life with a disability that left him with a limp. Because of various health issues, doctors predicted he wouldn’t live beyond his first birthday, but he proved them wrong. Despite not being able to participate in athletics, he was the manager of all the sports teams in high school and popular among his peers. His disability never seemed to get him down. “It would be the iciest day, and you’d see him sprinting on crutches,” she said.

He endured 18 surgeries on his leg. His leg was amputated the day after Greenberg, then 60, ran the Boston Marathon.“

One of her great pleasures for the past three years has been competing in the Miami half-marathon while pushing a woman with disabilities in a wheelchair.

Her role models include a handful of women who have represented the women’s 75-79 age group in Ironman events. She recalled a recent conversation with one such athlete, Cherie Gruenfeld, a former Ironman champion who now sticks to 70.3’s (half the full Ironman distance).

Greenberg asked Gruenfeld why she quit Ironman when she was on top. Gruenfeld’s answer was simple: She wasn’t enjoying it anymore. “So I think to myself, ‘Are you still enjoying this? Is this still fun?' ” Greenberg said. “And it is.”

While she happily gallops through races, astounded at how much faster she is in a race than during a training session, often dropping at least a minute per mile off her run pace, Greenberg keeps training fun by doing it with friends.

“I don’t have a day where I don’t have someone to meet,” she said.

While many triathletes hire personal coaches to design individualized training plans for them, Greenberg has always masterminded her own regimen, which gives her the flexibility to train with a friend or a group. Not only does the self-proclaimed chatterbox enjoy the time she spends connecting with her training buddies during a workout, she also appreciates the accountability.

While most of her younger competitors in Kona will cross the finish line around the 10-hour mark, she’ll take about 14 to 15 hours to finish.

She’ll be at the back of the pack overall — there will be about 2,500 participants in the race. But she plans to be ahead of the 75 or so people age 70 and older who, like her, qualified to be there.

She says she doesn’t mind having the course to herself.

“I just love the sport.”

Pam Moore is a writer and speaker in Boulder, Colo.

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