A Brazilian woman, a 73-year-old bicyclist from Fridley and an elite skier from Roseville lined up in the dark minutes before dawn on a northern Minnesota snowmobile trail. Ahead were 135 miles that would test their mettle in one of the toughest endurance races in the world — a competition so grueling that sometimes fewer than half the starters finish.

While a bone-chilling sleet pelted the racers at the 7 a.m. start on Monday, 94 bikers, 55 runners and two skiers were ready to power themselves in the Arrowhead ultramarathon from International Falls to Tower. The grittiest of athletes are lured by the course’s solitary wilderness as well as its inhospitable conditions — it’s held during what is usually the coldest part of the winter in what is considered one of the coldest cities in the Lower 48.

“What makes it ridiculously hard is that there is very little support,” said Ken Krueger, a seven-time Arrowhead finisher. He and his wife are the event’s race directors. “You have a convenience store as the first checkpoint, a second one at a resort and the third is a tepee in the middle of nowhere.” Outside support other than from fellow racers is forbidden.

Race organizers tout the Arrowhead as being “about you, the wilderness, your inner dogged spirit and self-sufficiency.”

By 7 p.m. Wednesday, 58 bikers, 28 runners and two skiers finished the race.

Carla Goulart, 39, a nurse from Brazil, arrived at Monday’s start in her fourth attempt to finish the race before the 60-hour cutoff time at 7 p.m. Wednesday. A veteran ultramarathoner, she didn’t want to be defeated again by the Arrowhead.

In her first try, in 2013, she arrived in International Falls never having seen snow before. “It was kind of exciting,” she said through an interpreter, Bernice Filha. But just days from the start of the race, it quickly sank in. “It’s really cold.”

A storm that dumped 12 inches of snow during the race forced her and many others to quit, Filha said. The next year, when racers faced temperatures that fell to 45 below, the petite, 124-pound Brazilian powerhouse towed 25 to 35 pounds of gear on a sled and finished in 60 hours and 10 minutes — 10 minutes short of being an official finisher.

In 2015, her feet sank into the wet, sloppy snow, and after 100 miles, they were blistered, bleeding and swollen. She dropped out.

This year, Goulart pushed through miles on snow that was soft rather than hard-packed — so rough that it threw racers off their bikes. “It was like running on loose sand,” she said. But 52 hours and 51 minutes later, she became the first female runner to finish the 2016 race.

On skis, Mike Brumbaugh, 57, of Roseville, wanted to test whether he could go longer than he ever had gone before. Then, about 20 miles in, disaster hit. His ski snagged a sapling and a pole snapped.

He skied 16 miles with one pole until he used a piece of PVC pipe and tape to jury-rig a repair. Despite the mishap, Brumbaugh rallied to a 22-hour finish, breaking the course record by five minutes. “I was just trying to finish and not injure myself,” he said. “People can freeze things out there.”

Next year, he may skip the skis and bike the Arrowhead.

That’s the hope of 73-year-old Irv Berglund, a two-time finisher, who was beaten by the course this year. “The snow was real greasy and then it would just break up like mashed potatoes,” he said. “You would hit a divot. It would just grab your wheel and then you would crash.” When his headlamp died and his auxiliary light ran low, Berglund bailed at 45 miles.

“Right now I kind of have this wet blanket of failure on my shoulders,” he said. “It bugs me that this thing beat me. As long as I’m still alive by next fall, I’ll try it again.”