Jo Pavey. Photo: Dean Mouhtaropoulos/Getty Images

On Friday morning in Rio, British endurance athlete Jo Pavey will run in the women’s 10,000-meter final. At 42, she’s the first British female track athlete to compete in her fifth Games. Two years ago, she won gold at the European Championships in the 10,000-meter, reportedly making her the oldest female athlete to win gold at a major international event — ten months after she gave birth to her second child, Emily, by cesarean section.

As she discusses in her autobiography, This Mum Runs, Pavey’s training is fit in with the duties of parenting. She paces 100 miles a week, squeezing in her second run of the day after the kids have gone to bed, with her husband (and coach) doing her physiotherapy before bed. “I don’t go to the gym,” she writes. “Instead I do exercises in the lounge, often while multitasking or with children sitting on me.” While Pavey has a host of competitors vying for the podium, the very fact that she’s competing in these Games is indicative of how older athletes are maintaining elite performance; this includes 41-year-old Uzbek gymnast Oksana Chusovitina, and 43-year-old American cyclist Kristin Armstrong — who just won her third consecutive Olympic gold, while also being the oldest woman in her field by seven years. This level of achievement, where Olympic-caliber performance extends into one’s 40s, shows how remarkably malleable the process of human aging is — and how the finest athletes can make physiological progress at stages of life when sedentary people decline.

With endurance sports, the main physiological driver is “maximal oxygen uptake” — how effectively your body can take oxygen from the air and deliver it to your muscles, where it’s converted into energy and pushes you down the track. (When athletes like Lance Armstrong engage in “blood-doping,” they’re artificially increasing their blood’s oxygen-carrying capacity). Mayo Clinic researcher Michael Joyner, who studies the physiology of performance, says that, in untrained people, oxygen-conversion capacity starts to slope off in their 30s.

“Maximal oxygen uptake is related to how much blood your heart can pump, and what happens as you age is your maximum heart rate starts to go down, limiting the amount of blood your heart can pump,” Joyner says. “But in people who continue to train very, very hard, their heart rate doesn’t drop as much and the amount of blood that can be pumped with each heartbeat can go up. And, as a result, they’re able to sustain their maximum cardiac output.” If you work hard enough — as Pavey does, despite her parental duties — then you can train your vascular system to keep supporting your muscles. It’s indicative of how much of a fountain-of-youth effect hard training can have on people; other research indicates that 70-year-old runners have the same walking efficiency as college students, and 80-year-old, lifelong cross-country skiers have the oxygen max of non-trained 40-year-olds. Indeed, Joyner says, if you train hard when you’re young, it can get that oxygen efficiency as high as possible; and if you continue to train as the years go by, you can keep it up there. As well, endurance-oriented type-one muscles — which you use when you’re standing — tend to stick with people as they get older, while explosive, type-two muscles wear down with time. And as sports like running have professionalized, athletes aren’t aging out in their 20s: They can make a living on the track. The average age of Olympians keeps going up, with endurance athletes as the oldest.

University of Exeter physiologist Andrew Jones, who’s supported Pavey on training trips abroad and done treadmill physiology tests with her, says that her longevity is in large part owed to her resilience; indeed, the injuries that have come up may have been inadvertently beneficial. “While no injury is ever good news, and Jo has had a few, perhaps missing several months of training on occasion has helped her body to recover from arduous training and helped keep her mentally and physically fresh when training resumes,” he wrote to Science of Us in an email. Having kids, he says, may have its benefits for performance: She’s had to focus her time effectively, and rather than stressing over preparation, she gets the training in when she can.

“When I was younger, I would get daunted by track sessions and spend the whole day thinking about hitting targets,” Pavey said in a recent interview. “Psychologically, it has been a massive boost that I have that balance and I don’t feel too tense or stressed.”

You also can’t discount how much of an asset those years of experience are for a runner. Humboldt State University kinesiologist Justus Ortega says that a part of the story might be “proprioception,” or the awareness you have of how your body is moving. “In older runners we look at, they are not only maintaining the cellular efficiency, but their bodies are able to process proprioceptive information so they’re not turning on the wrong muscles as much,” he says. “They’re maintaining an efficient activation of their muscles. They’re going to exhibit similar muscle activation as a young adult [would]. But with a sedentary person, you wouldn’t see the same efficiency.” And when people have practiced an activity longer, the stronger awareness they have, and the better they can use proprioceptive information in executing their skills, he says — whether it’s Michael Jordan, at age 35, shooting a championship-winning jump shot, or Pavey dialing in her running mechanics for the Olympics. Contrary to what your birthday tells you, aging isn’t absolute: Depending on what you do with your body, you can adjust it. Pavey is a prime example.