Alaska's 1,100-mile Iditarod Trail is famous for its dogsled race, an unmarked venture across ice-crusted lakes and windswept stretches of uninhabited land. Many consider it the ultimate test of frozen endurance, although those people probably haven't heard of the other Iditarod challenge.

"No dogs, no sleds, no help, just you in the wilderness," says 39-year-old R.J. Sauer. "Yeah, it might be a little crazier." On Feb. 23, Sauer and 55 other athletes will embark on the Iditarod Trail Invitational by bike, foot or ski, each knowing that only a fraction will finish. Since 2000, only 42 people have completed the 1,100-mile journey from Anchorage to Nome; in 2012 no racers reached the end.

"People are confused when they hear about it," says Sauer, who predicts the trek will take 20 days on his custom-made fat bike, which has tires that are nearly four inches thick and 26 inches in diameter. "Why? Why would you put yourself through that?" For Sauer, a filmmaker from Vancouver, it's the rush of testing his body's limits and the thrill of surviving in solitude. "It's hard to find a place in the world where you can disappear," Sauer says. It's even harder to survive where temperatures may dip below -40°.

Along with Frank Janssens, a Belgian who attempted the shorter, 350-mile version of the race last year (the two are run simultaneously), Sauer began preparing in April, aiming to log 500 hours of training. (At week's end Sauer was well on pace, at 465. His progress can be followed at monologblog.com, which also tracks how many calories he has burned: nearly 360,000 so far.) Cross-training is crucial; Sauer may need to push or carry his 55-pound bike for up to 400 miles. Using twice-a-week gym trips as a base—mostly lifting weights—Sauer varied his routines of hiking and biking, rarely repeating routes and almost never noting the mileage. "It's more about the hours you put in," Sauer says, "and the recovery."

A mild winter in Vancouver has allowed Sauer and Janssens to ride on the beach, where sand stood in for snow to help gauge the nuances of adjusting tire pressure. "It's like spinning," Janssens says. "Push too hard and you'll sink." That's why Janssens recommends napping midday (a sounder sleep when it's warmer) and riding at night, when the snow is compacted. Then again, go too fast and riders may sweat too much. Staying dry—Sauer does so by layering and using a quick-drying fabric next to his skin—is paramount for comfort and avoiding sickness. (Sauer had a scare this fall when he was sidelined for weeks by a superbug infection.)

At his peak physically, Sauer is now focused on gaining 10 pounds—whale blubber, if you will. He'll burn 10,000 calories a day on the trip and needs more than his allotted three 10-pound drop bags of fatty comfort foods to sustain energy. Some participants go as far as to eat sticks of butter. "Chomping it like it's a candy bar," Sauer says. Adds Janssens, "It's a race to test your sanity and your will."

And it's mostly a race for personal achievement. Only the winner takes home a prize: a waived entrance fee for 2015.

"Why would you put yourself through it?" says Sauer. "It's hard to find a place in the world where you can disappear."

PHOTOFRANK JANSSENS (BIKE)BRRRRIGHT IDEA In addition to endurance, Sauer has to work on strength so he can carry his fat bike when the terrain gets too tough. PHOTONOEL HENDRICKSON[See caption above] PHOTONOEL HENDRICKSON

HOLE YARDS PAR R1 R2 R3 R4
OUT
HOLE YARDS PAR R1 R2 R3 R4
IN
Eagle (-2)
Birdie (-1)
Bogey (+1)
Double Bogey (+2)