BRECKENRIDGE, Colo. — Guided by a dim light on the handlebars of his vintage mountain bike, 67-year-old Dr. Craig Louis Perrinjaquet leaves his home around 6 o’clock each winter morning, no matter how cold, dark, icy or snowy, and pedals uphill to the base of Breckenridge Ski Resort.

His ski poles are mounted to the bike frame with foam pipe insulation and his skis — 40-year-old Rossignol Randonnees — stick up into the air like a flagpole behind him, rigged onto the seat post with a bungee cord and hose clamps.

Fueled by a piece of fruit and handful of nuts, he wears outdated telemark boots, a ski helmet, mittens held together with duct tape and an 18-year-old jacket and snow pants, hand-me-downs from a friend. He waves at bus drivers and gets a friendly honk from passing cars.

Dr. Perrinjaquet, who has worked as a family and sports medicine physician for 30-plus years and is known as Doc PJ, leaves his bike near the base of the chairlift, which won’t start turning for another two hours. He clicks into his climbing skis and sets off up the freshly groomed run, the only sound . Slowly, the pre-dawn sky lightens to vibrant shades of pink and purple, magnifying the surrounding white peaks.

He reaches his turnaround point — a lodge near the top of the chairlift. The mile and a half-long hike takes him about 35 minutes. Sometimes, if he’s feeling giddy, he actually runs, on his skis, the last few yards to the top.

Dr. Perrinjaquet refers to the whole routine as “Type 2 fun,” a brand of “fun when it’s done” pleasure. But the pursuit of fun — Type 2 or otherwise — is not the only reason he does it.

“There’s this mystique about uphill that it’s so hard. Ski area uphill is low impact,” he said, referring to climbing the groomed and predictable slopes of a ski resort. “It’s really the safest, easiest thing to do. Some people might get bored doing it every day, but I love it. The wind and snow and sky are fresh every day. It’s my deal.”

Since the coronavirus pandemic began, uphill skiing, like many outdoor pursuits, has become tremendously popular. People the world over are marching up resort slopes, though most uphillers, especially those new to the pastime, would hesitate to call it easy.

“I always said, you’ll never, ever make me hike in ski boots,” says Petra Tibbitts, who bought gear for uphill skiing when resorts closed after the pandemic hit in March 2020. “Now, I just love it. It’s kind of your own battle, not just physical, but in your mind and ego. When I get to the top and turn around to see the sun coming up, it’s just so beautiful.”

Dr. Perrinjaquet’s uphill regimen has been a daily winter fixture for the last three decades.

“He’s part of the early vanguard of people doing it,” says longtime friend Jeffrey Bergeron, “but his uphill routine is probably the least interesting thing about him.”

At one point, Dr. Perrinjaquet was Michael Jackson’s tour doctor. A musician himself, he plays stand-up bass in a local band called The Pine Beatles. When he’s not schlepping up the slopes before sunrise or at his clinic, Dr. Perrinjaquet focuses much of his time on humanitarian work. He spent years traveling to Honduras and Nepal to provide free medical treatment, even putting a hard-working Nepalese teenager through medical school and paying for the construction of his clinic. They chat over Skype every Sunday.

Working with Dr. Tom Catena, a former nose guard at Brown University and subject of the recent documentary, “The Heart of Nuba,” Dr. Perrinjaquet spends several weeks a year volunteering at Mother of Mercy, a small hospital in the Nuba mountains of Sudan, bringing medicine and supplies to the war-ravaged country.

Although he didn’t travel last year, Dr. Perrinjaquet spent $81,100 on shipments of malaria and measles vaccines as well as various medicines and equipment.

“A new pair of skis doesn’t bring me much happiness, but a cargo plane of medical supplies makes me very happy,” he says, adding that his morning uphill ski routine is also a means of staying fit enough to survive a crisis in his overseas medical work.

“We all have our reasons to exercise, but I also want to be fit enough to, you know, run out of a war zone if I had to. A lot of the places I work are roadless, so I have to be able to walk and carry a pack a long way through the jungle or the mountains. That requires a certain level of fitness.”

A few years ago, he was in Sudan loading medical supplies into a truck when a terrorist fighter jet targeting the hospital roared overhead, dropping explosives throughout the village. After the bombing, Dr. Perrinjaquet carried supplies to patients who took cover in the caves, hanging IVs on trees and administering treatment with whatever supplies were available.

Growing up in the small farm town of Edgewood, Iowa, Dr. Perrinjaquet has been a dedicated vegan “since I studied gross anatomy in medical school.” An early practitioner of Transcendental Meditation, learned alongside Deepak Chopra, Dr. Perrinjaquet begins every morning with 20 minutes of meditation and does another 20 in the evening. He lives alone in a small home in town that he keeps just warm enough to prevent the pipes from freezing. He takes cold showers and wears second hand clothing. Other than a couple of sofas and a wood-burning stove that he uses for cooking and when he has company, his home is adorned with only a single picture frame that is kept empty to prompt the imagination of the beholder.

“He’s incredibly nonconsumptive,” Bergeron says. “I think he takes pleasure in being satisfied with less. It makes him feel like he’s part of the solution, not part of the problem. I’d be suffering if I lived like that. For him, he’s found an immense sense of satisfaction.”

Dr. Perrinjaquet says his early motivation for minimalistic living was a sense of solidarity with poor people, but now he’s also driven by his own experience.

“It’s not that I deprive myself. I’m happy with simple stuff,” he says, adding that his life is not entirely without comforts. He does have a hot tub, explaining how “after soaking in 104-degree water, I can sleep like a rat in a 40 degree house.”

Dr. Perrinjaquet would never call himself an athlete. But in the warmer months he also cycles, runs or hikes daily and competes in trail running events, wearing shoes he fashions out of old tires. In spring, he participates in a locally famous multisport event called The Imperial Challenge that requires competitors to cycle to the base of the ski resort, pick up their uphill ski or snowboard setup (not lug it with them on their bike like Dr. Perrinjaquet does) and climb to the highest point of the resort — an elevation of around 12,800 feet — before skiing or snowboarding down to the finish line.

As in his daily uphill routine, Dr. Perrinjaquet is not out for speed.

“I’m a solid, middle-third-of-the-pack guy,” he says. “The first third is pushing so hard, they’re suffering. Some in the last third maybe didn’t train at all and they’re suffering. The middle third, we are the ones out there that seem to be having the most fun.”