In 2015, Lazarus Lake, the race director of the Barkley Marathons, made a bold declaration: “This race is too brutal for women; they simply aren’t tough enough to finish it.”
Widely regarded as one of the most grueling ultramarathons on the planet, the race has seen about 1,000 starters in its history, yet only 20 have managed to survive the course and reach the finish line. At the time, Lake said he hoped someone would step up and prove him wrong.
Nine years later, Scottish runner Jasmin Paris did exactly that. With just 1 minute and 39 seconds remaining on the 60-hour cutoff clock, she crossed the finish line—caked in mud—becoming the first woman in the event’s history to complete the race.
This is by no means an isolated case. Rachel Entrekin not only shattered the record for the “Spine Race” (running from England to Scotland) but also claimed the overall victory at Arizona’s “Cocodona 250” this past May. Shortly thereafter, Sophie Woods took on the Alpine 1 route and slashed the existing world record by a full six days.
In these extreme endurance races—which often span days and nights of continuous, sleepless effort—women are no longer mere “also-rans.” They are closing the gap and even leaving top male competitors in their wake.
This has prompted the sports science community to re-examine a compelling question: As the running distance increases, does the physiological divide between men and women actually reverse?
In standard marathons and shorter races, the physiological advantages held by men are indisputable—greater oxygen uptake capacity and stronger bones and muscles typically result in male runners posting average times that are 10% to 12% faster than those of women. However, as the race distance is extended indefinitely, this advantage begins to rapidly diminish.
RunRepeat and the International Association of Ultrarunners (IAU) analyzed two decades of data on amateur ultramarathoners: at the 100-mile mark, the gap in average pace between men and women had narrowed to a remarkable 0.25%; once the 195-mile threshold was crossed, women actually outperformed men.
Endurance sports expert Andy Jones points to several often-overlooked physiological traits:
More efficient “fat-burning machines”: Women naturally possess higher body fat reserves and maintain more stable efficiency when burning fat for energy under extreme conditions, avoiding the “bonking” (hitting the wall) often experienced by athletes reliant on glycogen.
Innate endurance muscle fibers: Women’s muscles are richer in “slow-twitch fibers,” which are highly fatigue-resistant and exceptionally efficient at utilizing oxygen.
Slower endurance-related decline: During tens of hours of continuous, repetitive movement, women experience a significantly more gradual decline in basic muscle strength.
However, as many sports scientists acknowledge, hard experimental data on elite female ultramarathoners remains scarce; physiology is, at best, merely an entry ticket. What truly allows women to triumph on these grueling courses is the brutal psychological battle they must wage.
Faced with dozens of hours of sleep deprivation, extreme temperature fluctuations, and unexpected wilderness hazards, those who sprint hardest at the start are often the first to drop out. When New Zealand runner Sophie Woods broke the record for the Alpine course, she encountered a wildfire that forced a route change and was besieged by a massive swarm of horseflies: “I was in excruciating pain and wanted to just collapse on the ground and sob, but I didn’t dare stop—because if I slowed down, the horseflies would have eaten me alive.”
“It’s not about who can sprint the fastest; it’s about who can keep inching forward without complaint when everything is falling apart,” Woods said. Sports nutrition expert Renee McGregor offers a more grounded perspective: the mental resilience of many women has already been passively forged through the physiological trials of daily life. “From puberty onwards, women must constantly adapt to dramatic hormonal fluctuations. Not to mention the persistent nausea of pregnancy, the excruciating pain of childbirth, and months of severe sleep deprivation postpartum—these prolonged periods of discomfort are experiences many men never undergo. When stepping onto the racecourse, women possess a ‘reserve of pain tolerance’; they know they can endure, and they exercise great patience, refusing to recklessly gamble their lives on pace.”
Another often-overlooked “secret weapon” is the culture of the racing community itself. Yngvild Kaspersen, a Norwegian runner and two-time winner of the UTMB CCC race, notes the incredible solidarity and mutual support found within the women’s ultramarathon circuit. “We are competitors, but out on the grueling course—where the stakes can feel like life and death—we are more like comrades weathering a storm together; the psychological support we provide one another is immensely powerful.”
Regrettably, women still make up only about 20% of the starting fields in global ultramarathon events. Societal biases regarding female physical capabilities and the way rigorous training encroaches on family time remain significant, invisible barriers.
Yet, the tide is turning. For decades, the definition of “human limits” in exercise physiology was based almost exclusively on male subjects; however, as more and more female runners shatter records previously held by men, a realization is dawning on us:
We may never have truly witnessed the formidable energy a woman’s body harbors when she casts off constraints and runs with all her might toward the horizon.