At 77, she’s as fit as a 25-year-old. What her body tells us about aging.

Most runners see substantial performance losses after they turn 70. Not Jeannie Rice, who just turned 77 and ran the Boston Marathon in April.

She has broken world women’s records in the 75-79 age group for every distance and, at times, beaten the fastest men in that age group. At the Boston Marathon, according to unofficial results, her time was 4 hours, 27 minutes and 17 seconds. It was very slow for Rice, but she still placed first in her age group.

Rice is 5 feet 2 inches tall and weighs 95 pounds. Her physiology is striking: her maximal oxygen uptake (VO2 max) — a measure that reflects her aerobic fitness and endurance capacity — equals that of a 25-year-old woman, according to lab tests in the days after her World Record performance (3 hours, 33 minutes and 27 seconds) in last year’s London Marathon.

The tests were part of a case study of Rice published in the Journal of Applied Physiology.

Researchers are studying Rice to understand how humans can stay fit as they age, regardless of natural ability and the reduced physical activity often seen in older people, said Bas Van Hooren, assistant professor in nutrition and movement sciences at Maastricht University in the Netherlands and one of the study authors.

“She exemplifies how consistent training, and perhaps favorable genetics, can partly defy conventional aging processes,” he said.

Rice, a retired real estate agent, proves “it’s never too late to start exercising,” Van Hooren said.

Learning more about Rice will also help scientists “better understand the potential limits of human performance as we age,” especially “when exercise is performed at a high level over the adult lifespan,” said Scott Trappe, director of the human performance laboratory and a professor of human bioenergetics at Ball State University, who was not involved in the study.

Rice started running at age 35. Her goal was to drop the weight she’d gained during a trip to her native Seoul to visit family.

“I figured if I jogged around the block, I’d lose five pounds right away,” she said. “I was only running one or two miles at a time. I didn’t even have running shoes.”

Rice, who divides her time between Cleveland and Naples, Fla., decided to enter a few area races for fun, and won them.

A year later, she ran her first marathon in Cleveland without any serious training — she finished in 3 hours 45 minutes — and thought she probably could improve her time. Six months later, in Columbus, her second marathon, she did — by a whopping 29 minutes — running 3:16 and qualifying for the Boston race. She was hooked.

She recently ran her 133rd marathon in Tokyo.

(Although she ran slightly faster in the 2023 Boston race, 3:33:15, than in the 2024 London race, Boston’s point-to-point course makes it ineligible for record purposes.)

Rice doesn’t know whether she set any records in her 40s, 50s and 60s, although she regularly was winning races in her age group. “I never thought to check,” she said.

At age 69, she set an American record in the 65-69 division in the Columbus marathon. “That’s when I thought maybe I was a decent runner,” Rice said.

Her inspiration was Joan Benoit Samuelson, who set countless records during her long running career and won gold at the inaugural Olympic women’s marathon in 1984. “She was my idol,” Rice said.

Samuelson, 67, said that these days she’s the one who is inspired — by Rice.

“Jeannie is incredible,” Samuelson said. “Her times are even more impressive to runners who have been aging up in the sport. Her passion for running as she ages only seems to become more evident with her times and her desire to keep breaking age group records.”

Remarkably, Rice has almost never suffered an overuse injury — such as tendinitis or a stress fracture — although she has had accidents. Shortly before one marathon, she stepped awkwardly on a stone and twisted her ankle, “and it cost me seven weeks” of training, she said.

Among numerous tests, Van Hooren and Michele Zanini, then a doctoral researcher at Loughborough University (now a lecturer in exercise science at the Open University in England) had Rice run on a treadmill with increasing intensity while measuring her oxygen consumption and heart rate. They also drew blood to assess levels of lactate, a chemical produced when cells break down carbohydrates.

Lactate levels can be used to assess the transition from a “sustainable” effort to a “more strenuous” one, Van Hooren said. Researchers also analyzed body fat, muscle structure and capacity to use oxygen at her specific marathon running speed.

They found that Rice’s exceptional VO2 max suggested outstanding cardiovascular fitness, pointing out that the VO2 max of most untrained women between ages 70 and 79 typically is 45% to 65% lower than Rice’s.

“Her unique physiology allows her to be extremely competitive in any distance running event from the track to the road, a rare feat at the world-class level,” Zanini said.

Rice may be genetically predisposed to have a high VO2 max and cardiovascular efficiency, Van Hooren said. But other contributing factors could provide lessons on healthy aging, researchers said.

Consistent exercise: Rice runs 50 miles a week, or 70-75 miles a week when she’s getting ready for a marathon, with one day off. She also lifts light weights three times a week for upper body strength.

Balanced training and recovery: Her lack of overuse injuries suggests this balance, which has allowed her to maintain high mileage consistently over years, Van Hooren said. This may be key to high performance, particularly in older athletes, he said.

Healthy diet: She shuns fried foods and sweets and eats lots of salads, fresh vegetables, rice, fish and nuts, she said. Occasionally, she indulges in cheese, which she loves.

Passion and purpose: “When I asked Jeannie how she had managed to train consistently over 30 years, she simply replied: ‘I love running and being an example for younger athletes,’” Zanini said. Rice said she likes inspiring older runners, too. When people in their 50s and 60s say, “I’m too old to do that,” she tells them they are not.

“I feel as young as when I was 50, and I’d like to be doing this well into my 80s,” Rice said. “That’s my personal goal.”

A social life and other interests: Rice said she has a rich social life and enjoys going out to dance, although not in the week before an important race.

“A lot of runners are so serious they don’t do anything socially. But I like to have fun,” she said. “I’m the last one to go home.”

Gratitude: Rice can’t explain her gift but is grateful she has it. “Maybe I’m just lucky,” she said. “And blessed.”