PYEONGCHANG, South Korea >> For cross-country skier Martin Moeller, the biggest challenges of his sport are not the freezing cold, the hundreds of hours of training or the grueling toll of competition. It’s eating. And eating. And eating again.

“I actually do get tired of eating,” said Moeller, who lives in Greenland and skis for Denmark at the Olympics. “I always have to be thinking about what I will eat in two hours.”

Few sports ask as much of the human body as cross-country skiing, which engages virtually every muscle group — legs, arms, abdominals, back — for hours at a time. One of the enduring images of the long-distance cross-country events is the sight of athletes collapsing at the finish line.

That scene will no doubt repeat itself on this final weekend of the Pyeongchang Olympics as the men and women compete in their respective long-distance events — 50 kilometers for the men and 30 for the women.

Skiers can train four to five hours a day at their peak, covering 60 kilometers or more and pushing their bodies to the limit. As a result, cross-country skiers, on average, also have the biggest fueling demands of any Olympic athletes — winter or summer. While other sports certainly have their big eaters (Michael Phelps was famous for his enormous meals, which were not typical for most swimmers), scientists say the effort to stay in calorie balance is most daunting for cross-country skiers.

A typical elite cross-country skier will burn about 30 calories a minute during training — by comparison, a 155-pound person on an elliptical machine burns about 11 calories a minute.

Research has shown that a typical male elite cross-country skier must consume 7,000 to 8,000 calories a day — more than three times the caloric needs of an average male — to meet the energy demands of the sport. Female elite skiers must eat about 3,500 to 4,000 calories a day — about double the calories consumed by the average woman. (A Swedish study found that during the hardest training days it can reach 8,126 for men and 4,780 for women — about double the calorie needs of Kenyan marathon runners.)

What does it take to consume 8,000 calories — the equivalent of about 20 plates of lasagna or 40 scoops of ice cream — every day?

For cross-country skiers, who often have slim builds and limited stomach capacity, it means eating several times a day, and often planning their schedules around their constant meals. Many have tricks to help them fuel — they eat mashed foods, high-calorie bars, calorie-laden sports drinks; they carry backpacks full of beef jerky and almonds, and they always take dessert.

“I’m laughing about it and at myself because it feels normal,” said Caitlin Patterson, 28, a U.S. skier who finished 34th out of 62 in the 15-kilometer women’s skiathlon. “It is something we think about a lot of the time,” she said, as she snacked on beef jerky after a workout at the Olympic cross-country center. “It’s an important part of your job because fueling is so important for your physical performance.”

Patterson, who is 5-foot-9 and about 132 pounds, estimates she takes in up to 3,500 calories a day depending on her training level. Fueling starts with a breakfast of two eggs fried in butter topped with melted Vermont Cheddar, plus two pieces of toast with jam and no guilt. “It’s a good combination of the nutrients that I need to get through the training,” she said.

After morning training she quickly eats about 300 calories in snacks — beef jerky, almonds, a few Fig Newtons and maybe an orange. She eats lunch when she gets home. A big salad with maple-mustard dressing, a grilled cheese sandwich or quesadillas, followed by a cookie or a bowl of Ben and Jerry’s milk and cookies ice cream. After a few hours rest, it’s time to start thinking about eating again for her afternoon training.

Dr. Ola Ronsen, chief medical officer for the Norwegian Ski Federation, said that on many days the athletes simply cannot eat enough. Research has shown some may fall as much as 1,000 calories short of their body’s daily needs. As a result, it is important that they keep up the same eating routine on their days off to make up the deficit.

The problem, said Ronsen, is that many athletes feel full before they have entirely replaced the energy loss of training.

“When you train you take a lot of energy from the muscles,” he said. “But when you are replacing that, you’re using your stomach and gut to process the food before it’s brought back via circulation to your muscles. You’ve filled up your stomach, but feeling full is not always a reliable signal that it’s enough for the muscles to replace the glycogen.”

Moeller says that eating is such a big part of his day that it can sometimes interfere with family time with his sons, ages 6 and 8.

“My kids do say, ‘Do you have to eat again? Now?’” he said. “When you have to go out with the kids, I often say, ‘We have to wait. I have to eat.’”

Moeller, who is 6 feet tall and about 176 pounds, says he trains four to five hours a day and takes in about 8,000 calories a day, following a rigorous eating schedule to get it all into his body. In addition to eating a large breakfast (fried eggs, oatmeal and white beans), lunch (pasta with meat sauce, pan-fried fish and salad) and dinner (double servings of whatever his family is eating), he eats two smaller pre-training meals, two small recovery meals and a small extra meal before bedtime (any combination of oatmeal, bread, cheese, ham, honey, sports drinks and sometimes cheesecake or chocolate cake or a doughnut if he wants it.)

This summer, Moeller adjusted his diet to eliminate sugar and focus on only “healthful” foods.

“I lost a little weight but I was not skiing faster — I was skiing slower,” he said.

He decided to go back to eating whatever and whenever he felt like.

“When you have to eat a lot, you have to eat the stuff you like to eat,” he said. “It’s not eating cake all the time of course. You need to eat all the healthy stuff. But it’s not good to say this is something I can’t eat. If you want a doughnut or a Coke, you get a lot of calories like that and you recover much faster. It’s better than eating less.”

During weeks of strenuous training during the season, the athletes are pushing so hard that their bodies begin to release hormones that suppress appetite, making it an even bigger challenge to get the necessary nutrients.

“If you come to a point where the training is so hard your desire to eat goes down, that’s a critical balance,” Ronsen said. “It’s a delicate situation. You really have to force yourself to eat even though you don’t feel like you are hungry anymore.”

Susie Parker-Simmons, a senior nutritionist for the U.S. Olympic Committee, said that meeting the calorie demands of the sport can be especially challenging for women, who can lose their menstrual cycle and bone mineral density if their eating falls behind. “It’s just so hard to get that amount of calories in,” she said. During a team event in Switzerland, she worked with the athletes to help them fuel, recommending that they take in calorie-dense foods right after training like sports drinks and gels, Clif bars, smoothies and peanut butter and jelly sandwiches.

“They said, ‘If you come look after us we’ll just eat or drink what you give us,’” she said of the U.S. skiers.

Linda Bakkman, a sports nutritionist with the Swedish Olympic Committee, said that even Olympic athletes must contend with cultural biases around eating high-calorie foods.

“You can’t meet the energy requirement of being a cross-country skier with salad,” she said. “There is an educational challenge.”

Swedish cross-country skier Daniel Rickardsson, 35, who won Bronze in the 15-kilometer event in Sochi in 2014 and who will compete in the grueling 50 kilometer Saturday, said that fuel is a constant need. During a race, which can last a few hours, he needs to consume about 100 grams of carbohydrates every 15-20 minutes. A crew member hands him a high-concentrate sports drink at regular intervals on the course.

It helps that he spends time with teammates who also eat three regular meals each day (porridge, cheese and meat sandwiches, quinoa, tuna, chicken, vegetables) plus six small meals, including one before bedtime (high-protein yogurt, banana, eggs, cheese sandwiches.)

“It’s breakfast, training, lunch, rest, eating, training, eating and rest and eating,” Rickardsson said. “It’s what we do.”

For Moeller of Denmark, who finished about 6 minutes behind the winner in the men’s 15-kilometer freestyle cross-country event, Pyeongchang is likely to be his last international competition, although he still plans to continue skiing and to run marathons.

“But I’m looking forward to relaxing and not training so much,” he said. “And I’ll eat a lot less.”

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