After a 300-pound boulder shattered his leg, Dave Mackey—one of the world’s elite long-distance, off-road runners—had to work hard to learn how to recalibrate to his new life and return to the sport with a prosthetic limb. Now, the 48-year-old is on track to reclaim the joys of running again.

It’s early February 2018, and Boulder-based ultra runner Dave Mackey is in Texas toeing the start line of the Bandera 50K. This is the first race in three years for the chiseled, thoughtful Mackey, who has been named the U.S. ultraruner of the year three times and once held the record for the fastest known time from the South Rim of the Grand Canyon to the North Rim and back again. It’s also his first race with a prosthetic limb.

On May 23, 2015, Mackey was in the middle of a long run, but really nothing out of the ordinary for him: He set out to top three peaks, totalling up more than 8,000 feet of climbing over about 20 miles in Boulder Mountain Parks. Bear Peak, topping out at 8,461 feet with an exposed rocky summit ridge, was peak number two. On his way to peak number three, however, a rock gave way underneath Mackey’s shoes. He hurtled 60 feet down a jagged scree field, eventually slamming to a stop with massive 300-pound boulder pinned to his lower left leg, his tibia and fibula shatteed.

“It was a survival situation,” he says. “From the moment that I stepped on the rock and it slipped—in that split second—it was reflex and reaction. I kept myself alive. I was somehow able to control my body as much as you can when you fall backward off a mountain and land on your back.”

Broken and trapped, Mackey bellowed for help. Luckily, it arrived within minutes, but thick fog and rain precluded an emergency helicopter landing. Rescuers carried the fallen ultrarunning champ off the mountain in a rescue that took the better part of the day.

“I wasn’t bawling because the first rule is survival. Don’t panic. Control,” he says. “Luckily my friends showed up and they were literally holding me in their arms to keep me from falling off the peak. They were cradling me to keep me from sliding.”

The rescue was only the beginning of his ordeal. “The first couple weeks after the accident, there was so much processing about what to do with the injury and surgeries,” Mackey says. “I was in the hospital and they were putting in hardware and taking it out, dealing with infection. I really was focused on that. I wasn’t thinking about the emotional aspect of what happened.”

The real crusher: His leg would never be the same. After 13 reconstructive surgeries in 16 months, he eventually healed enough to walk without a cane. But Mackey couldn’t run. More, his body seemed determined to make life difficult. Pain and multiple infections foretold a future of more surgeries and setbacks.

After weighing the options, Mackey chose to have the ruined limb amputated below the knee, rather than deal with ongoing pain and infection. The night before surgery, Halloween 2016, more than 100 people came out to a leg-going-away party at Flatirons Running in Boulder, where sinewy runners quaffed donated microbrew and signed Mackey’s dead flesh with a sharpie.

In the aftermath of that grim choice, Mackey hoped for a quick recovery. Rid himself of the bum leg, he figured, and he’d step back into the high-octane life that defined his pre-injury days. Amputation wasn’t a magic bullet, however. The pain persisted. Fitting the prosthetic turned out to be equal parts art and science, and finding the right fit took time.

In the summer of 2017, about seven months after amputation, Mackey cancelled plans to climb a volcano in Ecuador. He also set aside his goal to compete in Leadman, a series of trail run and mountain bike races in Leadville, Colorado that total 282.4 miles. But he didn’t stop working or moving—first walking, then hiking and biking and, eventually, running.

Then he was there in Texas, racing again. But it was going to be diffetent now. The longest distance Mackey ran since amputating his leg before competing in The Bandera 50K was 13 miles. Despite that, he says he was not worried about the distance.

“My goal was to finish and not hurt myself further,” recalls Mackey a few weeks after the race. “I thought maybe I’d develop some abrasions or muscle issue but that didn’t happen. It felt smooth.”

Smooth enough to finish 37th with the respectable time of five hours and fifty-eight minutes, not a podium, which is where Mackey regularly landed pre-accident, but enviable to the majority of runners who enter long-distance trail races. Not that Mackey cares what you think of his finish. A native of Maine, the quiet, 48-year-old father of two has built a life outside of traditional conventions, choosing a career with flexible hours (physician’s assistant) that provides a paycheck but also leaves plenty of free time for exercise and family.

“Dave looks to break new ground, challenge himself and expand what’s possible,” says Mike McManus, Senior Sports Marketing Manager at HOKA One One, Mackey’s footwear sponsor since 2010. “He has a remarkable ability to stay positive, believe what’s possible and make it happen.”

Mackey wasn’t always an elite athlete, however. For years he led Outward Bound trips before discovering adventure racing, a team effort where competitors navigate unmarked wilderness via multiple disciplines. From there he moved on to ultra running and quickly distinguished himself. In 2004 and 2005 he was named USA Track and Field Ultra Runner of the Year; in 2011 he won the Montrail Cup and his first Ultrarunner of the Year title. Yet those who know him in contexts outside of trail running would never know of Mackey’s bona fides. In Boulder, a town filled with accomplished athletes who clamor about their latest extreme feat, Mackey is a throwback to the humble old guard, akin to a Swiss mountain guide who would never commandeer the conversation for the sole purpose of lauding himself.

“You could spend days with Dave and not have any idea of his success,” says Mackey’s former adventure racing teammate and pro runner Adam Chase. “Part of it is New England humility and part is his own identity. He thinks of himself as his kids’ dad. He takes pride in helping people heal themselves. What he does as an athlete doesn’t define him, at least not in his eyes. To trail runners, it’s another story. He’s legendary.”

After surviving his accident, Mackey became famous to a wider audience, as news spread of his bravery in the face of the gruesome ordeal and the choice to amputate. Many runners looked to Mackey for inspiration or answers to deeper philosophical questions. To his thousands of social media followers who were shocked when he was injured, and whose devoted following to his recovery can be tracked in the hundreds of comments he receives on Instagram updates, Mackey is simply an inspiration. A film crew traveled with him to Bandera, and Motiv Running, a website devoted to all things running, released a short documentary on Mackey’s recovery in January. Best of all, he will be inducted into the Colorado Running Hall of Fame on April 10.

“Dave doesn’t have to win to keep going,” Chase says. “The fact that he’s able to go on with life as though nothing has really happened and to live a rewarding life is one reason so many people look up to him.”

Make no mistake—it’s a pain in the ass having one leg. Even though most days Mackey says he doesn’t notice his prosthetic, his physical change demands more thinking—which blade does he need for an adventure, the running blade or the attached foot?—and dealing with stares or questions. And there’s the fact that he’s probably not going to set a speed record for climbing the state’s 14,000-foot peaks, something he considered doing before his accident, or even just win races like he once did.

But with one post-amputation 50K in the bag and at least two more on the calendar—he recently registered for the Dirty 30, a 50K race in Golden Gate Canyon State Park and he has entered the 2018 Leadman—Mackey is back. He’s grateful to be running without pain—prior to surgery, he was plagued with infections in his injured leg. He got out skiing this past winter, and, this spring, he’s riding his mountain bike. In other words, Mackey has taken the loss of both his leg and his status as an elite ultra runner in stride.

“Before the accident, I loved what I was doing,” he says. “I loved training, getting out, going to events and doing the best I can. The only difference now is I don’t do it to win, I do it to complete the thing.”