In July 2014, a shy 16-year-old named Lynzi Doke edged herself into a mob of very fit runners and very big donkeys on the main street of Fairplay, Colo. She felt sick to her stomach. This is a big mistake, she realized, but it was too late: A shotgun blasted, the donkeys stampeded, and the World Championship Pack Burro Race was underway.

Lynzi had to sprint just to avoid getting trampled. Jostling around her were more than 50 men and women, all of them running side by side with their own galloping animals. Lynzi tightened her fist around the lead rope of Chuggs, a beast of a burro she’d borrowed that outweighed her by a good 700 pounds, and tried to breathe in the thin mountain air. Looming ahead were 15 miles of dirt trail, climbing to a peak at more than 11,000 feet.

Lynzi had never run that far in her life, let alone attached to a donkey, but one thought gave her hope: When it comes this extreme sport, women are superb.

Burro racing sounds like a stunt, but it’s actually a grueling and fiercely competitive Rocky Mountain tradition. It dates back to Gold Rush days, when lucky prospectors were said to have thrown their gear on their donkeys’ backs and run to the nearest town to register their claims. Miners began challenging each other to 20-plus-mile races across the mountains to test their raw stamina and skill at handling a half-ton animal that can kill with a kick. Over time, burro racing attracted world-class athletes, like the Olympic-caliber cyclist Barb Dolan and the five-time snowshoe world champion Tom Sobal, who found it both humbled and exhilarated them like nothing else.

The sport crossed my radar because I’d gotten myself into a bit of a jam. One of my neighbors in Lancaster, Pa., had asked if I could take in a poorly treated donkey he was trying to rescue from a neglectful owner. Sherman arrived at our home in terrible shape, with rotting teeth and hooves so dangerously overgrown, he could barely walk.

But he needed even more than veterinary care, I was told; to truly revive Sherman, I’d have to find something to engage his mind and body. I liked the idea of making him my partner in a long-distance race, but could he pull it off? Could I? Sherman had damaged feet and a battered spirit. I had zero animal-training experience and no clue whether I could get him — and myself — in shape for something so demanding. As a team, we were pretty hopeless.

That’s how Lynzi became my coal-mine canary. If a teenage girl who twice survived a Code Blue could handle this race, maybe Sherman and I had a chance.

“People who knew Lynzi as a child can’t believe she’s even alive,” Lynzi’s mother, Kelly Doke, told me. “Her heart and lungs were so weak, she had a 10 percent chance of survival. But as soon as she heard about burro racing, she was dying to give it a try.”

Lynzi was born with a severe infection that allowed fluid to gradually fill her lungs. She went into respiratory arrest at six weeks old, beginning a cycle of near-death struggles that went on for years. Her heart became so weakened that just living in Colorado, where high altitude makes it harder to breathe, could eventually kill her. So the Dokes immediately sold everything and moved to the flatlands of Missouri, where they spent the next decade paying off their crippling hospital bills and nursing Lynzi back to health.

“In middle school, Lynzi began running cross-country to see if it would strengthen her lungs,” Kelly said. “It made her so much stronger, and she actually got really good at it.” By the time she was ready for high school, Lynzi had recovered enough for the family to move back home to Colorado. During a visit to the dentist, they discovered the hygienist was none other than Barb Dolan, the burro-racing legend. They got to chatting, and soon after, Barb made an extraordinary offer: She was ready to retire from competition, so if Lynzi was up for the challenge, she could race with Barb’s champion burro, Chuggs.

Lynzi was thrilled — until she found herself at the starting line a few months later. Luckily, the Pedretti brothers were there to help. Rick and Roger Pedretti are dairy farmers from Wisconsin who trailer their donkeys more than 1,000 miles every summer to compete as a tribute to their brother, Robert Pedretti. He won the Pack Burro World Championship in 1999, but struggled with depression and ended his own life in 2004. Every year since then, the Pedretti clan has made the pilgrimage to Fairplay.

“Just stick with us,” the Pedrettis told Lynzi. The brothers stayed by her side for the first 10 miles, until they suspected they might be holding her back. “You got this,” they urged. “Go for it!” With five miles to the finish, Lynzi and Chuggs left the Pedrettis and began moving through the pack. Soon, she was within eyeshot of John Vincent, the three-time champion who was currently in first place.

John wasn’t too surprised that Lynzi was on his heels. For years, women have gone toe-to-toe with male burro racers and often won. Barb Dolan has captured nearly every title on the circuit, including a first place in Leadville at age 54 (finishing a half-hour behind her in second was a man 10 years younger). She and Karen Thorpe owned the 2011 World Championship, with Barb winning the short course and Karen sprinting to win the 29.5-mile-long course by one second.

So why do women get stronger as distances get longer? After all, the first athlete to swim from Cuba to Florida without a shark cage wasn’t Michael Phelps but 64-year-old Diana Nyad. One of the world’s best obstacle course racers is Amelia Boone, a 34-year-old attorney who consistently defeats nearly every man in 24-hour contests. Pam Reed was 41 when she won the 135-mile Badwater ultra across Death Valley in 2002, then returned the next year to do it again. But the greatest hero of them all must be Emily Baer, who outran dozens of elite male ultramarathoners in 2007 to finish eighth overall at the Hardrock 100 — despite stopping to breast-feed her baby at the aid stations.

There are lots of theories about why women excel at endurance sports. Is it better fat metabolism? A higher pain threshold to deal with childbirth? More self control because of lower testosterone? But maybe the mystery isn’t really all that mysterious. We’ve been conditioned to believe sports are all about power, since most games we see on TV were created by men, for men, to show off two male attributes: bulk and speed. But compared to other species, we’re actually pathetically small and slow (Care to wrestle a grizzly, or race a puma?). As human animals, we have only two real athletic skills: stamina and ingenuity. That’s where we’re at our best — when we have to go long and think hard — and it’s also where men and women are most alike.

“Out West, we’ve always known that women were cut from the same leather as men,” said Curtis Imrie, the great burro sage who liked to point out that long before women were permitted to run marathons in Boston or the Olympics, they were running ultramarathons in the Rockies. “Burro racing has none of that nonsense you have back East about ‘protecting’ women.”

Curtis passed away recently, but he was there when Lynzi Doke battled her way to the finish of her first World Championship. She crossed the line in an astounding fourth overall, beating more than 50 other runners and putting a smile on Curtis’s face.

“That gal is the real deal. Latest in a long line of women in this sport who are incredibly fit, very competitive, and have the knack for training animals,” Curtis said. “Why wouldn’t they beat all the men?”