Caroline Boller, winner of the 2016 Brazos Bend 50-mile trail race

Ed. Note: The full article appears in the May issue of “Outside” Magazine. The excerpt here is reprinted with permission.

Among the world’s the Ultra Trail du Mont Blanc is known for being particularly brutal. The 106-mile course through the French, Swiss, and Italian Alps climbs more than 33,000 feet as it loops around its namesake peak. The weather can be savage—heavy rain, frigid nights, hot and humid days.

In August 2013, Rory Bosio took off from the start line without grand expectations, having never won a major event. She trailed well behind the leaders for the first six hours. But as the race stretched into the evening and most competitors slowed, Bosio held her pace. When the lanky, brown-haired American runner in pink shoes and a blue running skirt crossed the finish line in 22 hours 37 minutes, she’d destroyed the women’s record by two and a half hours. Bosio took seventh place overall, becoming the first woman to crack the top ten at the event and beating dozens of elite pro men.

It wasn’t the first time a woman broke through at a major endurance competition.

In the early aughts, Pam Reed won consecutive 135-mile Badwater Ultramarathons. Back then her victories were considered anomalous, especially since the next fastest women were more than seven hours behind her.

Bosio’s Mont Blanc race, however, is just one of a recent string of noteworthy female performances. A year earlier, obstacle racer Amelia Boone took second overall at the World’s Toughest Mudder, a 24-hour championship race during

which she covered 90 miles. She finished a full ten miles ahead of the third-place finisher, also a woman.

In one weekend this past December, women took five outright victories in ultra marathons across the country, with 42-year-old Caroline Boller setting a new course record at the Brazos Bend 50-mile trail race in Texas.

To be clear, female victories in mixed-gender events remain rare. In the marathon, top women finishers are about 15 minutes slower than the top

men. But the growing number of standout performances by women in ultra-distance events has athletes, coaches, and researchers believing that women may still be far from achieving their full potential as athletes.

The sentiment is buoyed by the simple fact that women have been competing

in endurance sports in large numbers for a relatively short amount of time.

The consensus among scientists is that men have several key physical advantages over women that make their edge at the elite level insurmountable in all but a few highly specialized sports. But they also concede that we’re only beginning to understand what women endurance athletes are capable of. A growing pattern of race results suggests that the longer and more arduous the event, the better the chances women have of beating men.

Most of the progress was the natural result of women getting a fair chance to compete. Fewer than 300,000 girls played high school sports before 1972; today more than 3.3 million participate.

“Women’s fields are growing fast and records are falling,” said Rebecca Rusch, 43, a seven-time world champion mountain biker who has competed against men in endurance events for 25 years. Which just means we haven’t gotten anywhere close to maxing out our genetic capabilities yet.”

In endurance sports, five phys  ological factors play a big role in determining athletic potential. Men have definitive advantages in three of them—heart size, lean muscle mass, and VO2 max (the body’s ability to deliver oxygen to muscles).

But then there are those other two, central drive and movement economy. The former is the rate at which the nervous system sends signals to muscles and is critical to maintaining an intense effort over time. The latter is how efficiently the body moves, which is dictated by coordination and joint stability.

Both central drive and movement economy can be improved through training, and along with a host of smaller variables, they may have an equalizing effect on male and female athletic potential, especially in endurance sports.

“Proper form counts way more than many athletes realize,” says May Clinic Michael Joyner, a renowned expert on health and human performance. “Depending on the sport, you can often overcome having a smaller engine if you are a better driver.”

Then there’s the mental game. Here women come out ahead in the key art

of race pacing, a trainable skill that men seem to have a harder time refining.

According to Danish statistician Jens Jakob Andersen’s massive marathon

study, female runners pace 18.6 percent better over the course of a race

than males.

“Men may be more likely to adopt a ‘risky’ pace where an individual begins the race with a fast early pace (relative to their ability), and this increases their likelihood of slowing later,” Anderson wrote in his analysis.

Put another way, the boys blow up.

What is certain: everyday more and more girls and women will play sports. They will continue to close the performance gap with men. And in those crazy-long distance races when, many hours in, everything hurts and the guys who went out way too fast are bonking, and others are stopping every 30 minutes to suck down an energy gel, women will breeze past them on their way to the finish line.

Meagen Brown has beaten hundreds of men since she started racing ultramarathons in 2012.