These women joined a growing list of women who are not only catching up with men in endurance races but actually surpassing them. My favorite example is Jasmin Paris, who won the winter edition of the Montane Spine Race in 2019. At the time, her daughter was one year old, and she stopped at checkpoints to express breast milk. Not only was she the first woman to win the race, but she also obliterated the course record by twelve hours.

These women are part of a wider story in the world of endurance sports. The longer and harder the race, the closer women’s times get to men’s—and in some cases, they surpass them. This fact has the potential to upend the entire way we view physical differences between cis-men and cis-women.

The idea that cis-men are, on average, faster and stronger than cis-women is accepted as a universal truth. Sport has been framed around it for decades—it is why men’s and women’s categories exist in the first place.

This same idea has been used to dismiss women as the so-called “weaker sex,” to justify unequal investment in women’s sport, and to demonize trans women, as well as women who don’t fit certain aesthetic standards of femininity, for wanting to take part in professional and even amateur sports events.

In many cases, cis-men indeed outperform cis-women in sports. But while men’s speed and strength dominate shorter events, endurance sports seem to level the playing field—and sometimes tilt it in women’s favor, as is evident in ultra-running, but also in biking and swimming events.

In 2019, American cancer survivor Sarah Thomas became the first person—male or female—to swim the English Channel four times without stopping. The same year, German cyclist Fiona Kolbinger, then a 24-year-old medical student, won the Transcontinental Race, a 2,500-mile bikepacking challenge across Europe.

Research backs up what the anecdotal evidence suggests. A large-scale study led by researcher Paul Ronto, analyzing results from over 15 000 ultramarathons and five million runners between 1996 and 2018, found that women consistently close the performance gap as the distance increases.

At short distances, men hold a clear edge: their average times are 17.9 percent faster over 5Ks and 11.1 percent faster in marathons. But once the races stretch into ultra territory, the difference narrows dramatically. By the time runners reach 100 miles, the gender gap shrinks to just 0.25 percent. Beyond 195 miles, women actually average 0.6 percent faster than men.

These figures are presented with several layers of nuance that must be taken into account. The study compares the entire cohort of men participants and women participants. Since fewer women take part in ultramarathons, the data is slightly skewed. As the early adopters of the sport, they tend to be more dedicated and higher performing, whereas a greater number of amateur men have begun taking part in the races, lowering the average.

At the same time, this lower participation also means women’s potential ceiling hasn’t been fully tested. If more women took part, some results would shift downward as amateurs entered the field, but there would also be more high-performing athletes to push the limits even higher.

More research is needed to confirm women’s advantages in endurance racing. But what we do know for sure is that women are already winning thirty ultramarathons in North America each year. That might only be around 1.5 percent of events, but it is still significant enough to disrupt the narrative that men are biologically destined to dominate.

So why are cis-women thriving when the mileage stretches into the hundreds? Science points to several advantages rooted in the female body.

• Fatigue Resistance
  Muscles are composed of two types of fibers: type I, or slow-twitch, and type II, or fast-twitch. As their names suggest, type I fibers are made for endurance. They contract more slowly and can work for extended periods. Type II fibers generate more force but fatigue rapidly.
  A 2015 study showed that women have more slow-twitch muscle fibers than men, allowing them to sustain muscle function for longer and recover more quickly during prolonged effort.
• Energy Efficiency
  One of the biggest challenges ultra-runners face is fuelling, as the body has to constantly replenish energy stores while on the move. The easiest energy source for the body to use is glycogen, a sugar stored in the muscles. But during long races, this is quickly depleted.
  An advantage that women have over men is that they have more estrogen, which promotes the use of fat as fuel and the conservation of glycogen. This means that those easily accessible sugars last longer during the race. Studies show women can have up to 56 percent higher fat oxidation rates than men, giving them a metabolic edge as the miles mount.
• Mental Resilience and Pain Management
  There is also evidence that women process pain differently from men. A 2019 study in Current Biology found that men tended to remember painful experiences more vividly and were more stressed when encountering similar discomfort again, while women appeared less affected by prior pain.
  Other research suggests women are less susceptible to mental fatigue as they age, maintaining focus and motivation through long efforts.
• Pacing Strategy
  While physiology matters, psychology and tactics are equally important. Studies consistently show that women are better at pacing themselves in endurance races. Analysis of more than two million marathon results between 2009 and 2019 revealed women were 18.33 percent better at keeping an even pace than men.
  Men, influenced partly by testosterone-driven risk-taking, are more likely to start too fast and fade. Women’s more conservative pacing helps prevent burnout and maintain strength deep into long races.

Meanwhile, the physical advantages that make men stronger and faster in short events lose their edge in longer bouts of endurance.

“One of the reasons why women tend to be able to compete with men and sometimes outperform them is that the greater maximal capacities exhibited by men aren’t as important in an ultra-endurance event,” explains Dr. Nicholas Tiller, an expert in applied physiology and ultramarathon runner, to the BBC. Anatomical differences in men, such as larger hearts, leaner muscles, and greater aerobic capacity than women, make them faster and stronger, but they lose their advantage over long distances.

Inspired by incredible runners like Jasmin Paris and Anna Troup, breaking records well into their forties and fifties, I started ultra-running this year. Last month I took part in my first event—a 45-mile race through the mountains of Bulgaria.

I am excited to see what happens as more women take up ultra-running—we currently only make up around 10–20 percent of participants. As that number grows, so will the epic victories that definitively destroy the myth of women as the “weaker sex.”