The grueling Arrowhead 135 ultramarathon starts Monday in International Falls. Touted as one of the toughest races in the world, the 14th annual competition has drawn athletes from around the county and the world.

The state of Minnesota, however, boasts both the youngest and oldest participants in this year's event, a 135-mile race across the northern Minnesota wilderness on foot, bike or skis that ends near Tower. Erv Berglund, 75, of Fridley, Minn., is looking for his third finish in the grueling race, which often sees a large number of entrants drop out.

"Both times I finished I felt totally spent," said Berglund, who will be biking the race. "It's a brutal, tough ride."

At the other end of the age spectrum this year is Tyler Firkus, 25, from the St. Paul area. He'll be experiencing the Arrowhead 135 for the first time.

Berglund said one of the greatest challenges for competitors in the round-the-clock race is maintaining a comfortable body temperature.

"Overdressing becomes a real issue for a lot of people," Berglund said. "You need to be familiar with the layers you have on. You can always stop along the way to pull something out of your bag as an extra layer."

Temperatures along the trail during the race have reached as low as 45 below zero including wind chill. Conditions this year are forecast to be relatively mild with a chance of snow, which can bring challenges all its own, according to race director Ken Krueger.

"Weather and trail conditions really drives the success rate," Krueger said. "Warmer trails are soft, so you have to work harder to go slower."

More than 40 out of about 150 entrants this year are choosing an unsupported option, meaning they are not allowed to stop at any of the three checkpoints along the way.

"The difficulty in conquering it is getting to someplace comfortable and then not wanting to go back out and wanting to end the suffering," Krueger said.

The cutoff to finish is 7 p.m. Wednesday at Fortune Bay Resort Casino.

Despite the often-extreme weather conditions, and the physical and mental challenge, racers tend to keep coming back.

"This is probably the fastest the roster has ever filled," Krueger said. "About two-thirds of the roster are returning racers, and we had to cut off rookie registration after just two days."

Firkus, the Arrowhead 135 rookie, said that his key to finishing is staying focused.

"It's really more of a mental thing and keeping your head in the right place," Firkus said. "I also like to listen to podcasts."

As the youngest competitor on the roster this year, Firkus has one particular goal in mind: beating his dad Jeff, who has completed the race before.

"I can't let him pass me," Firkus said. "I'm skiing and he's running, which is part of the reason I can't let him beat me."

For more information about the Arrowhead 135 and for race results, go to www.arrowheadultra.com.