At 19 years old, Kris Freeman passed on a full ride to college to train with the U.S. ski team in Park City, UT. Twelve weeks into training, high blood-glucose levels found during his routine blood test led to a diagnosis of type-1 diabetes. The condition, in which the pancreas produces little to no insulin, is incurable but treatable. Still, doctors were skeptical and told Freeman a career as a skier was over.

“I was crying, I was in shock, and really terrified,” says Freeman, who decided to stay in Utah to train. “I didn’t know anything about diabetes.”

Between training sessions, he educated himself about the disease and became determined to pursue being a cross-country skier.

Freeman’s persistence, along with better glucose monitors and improved insulin, proved the doctors wrong and inspired him to keep skiing. Now he uses advanced pumps to monitor his blood-sugar levels, continues to tweak his pre-race ritual of meditation, yoga, and calming music—high stress levels can spike blood sugar—and constantly adjusts his insulin injections and food intake to account for fluctuations in energy expenditure.

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Freeman, 36, spent the past 16 years becoming one of the top skiers in the world. He captured 17 U.S. Championships and is now prepping for the 2018 Winter Olympics, his fifth, and more than any other American cross-country skier.

Despite the reality that he’s past his prime, his training is relentless. Freeman logs more than 800 hours of cardio per year—a 27.5-mile session on roller skis (pictured) is “normal,” and on his intense days, he ramps the mileage up to 50 or 60 unless he’s cycling, then it’s 100. He barely touches weights, except for some core work, but you’d never guess by looking at him. His shredded physique is the product of razor-sharp focus and meticulous nutrition. His daily caloric intake ranges, depend- ing on his workouts, between 3,000 and 6,000. Because he has to control his insulin levels, Freeman sticks with low-glycemic, protein-based foods, using carbs strategically to manipulate his blood sugar.

“I’m always running a math equation in my head as far as how much insulin I need, how much glucose is coming on, how much further do I have to go,” explains Freeman. “Spontaneity is not an easy thing with [diabetes], but with a little bit of planning I’ve pretty much proven you can do anything.”