COEUR D'ALENE, Idaho (AP) — Imagine swimming 2.4 miles, cycling another 112, then running a marathon.

Now imagine doing it blind.

A pair of northern Idaho Ironman race veterans have signed up to each lead a blind competitor around the 140.6 mile course at Kentucky's installment of this long-distance swim, bike and run series next Sunday.

Nate Birdsall, 22, of Coeur d'Alene, and Scott Burkhardt, 45, of nearby Post Falls, say training for such grueling races is normally a self-absorbing experience, one where they spend hours and hours and hundreds of miles alone on the road.

Come the Louisville event, however, these men will be concentrating on somebody else — somebody they have yet to meet in person — to bring them exhausted but safe to the finish line.

"I met a couple of them at the 2005 Ironman," Burkhardt told the Coeur d'Alene Press, remembering that year's version of the event in Coeur d'Alene and blind athletes and guides he encountered along the way. "I was having a tough race, but when I met those guys I was instantly humbled."

In Kentucky, they'll be volunteering with Fort Lauderdale, Fla.-based C Different Foundation, which helps visually impaired individuals take part in events like Ironman races.

There, they'll swim tethered to somebody else with an elastic cord; mount a tandem racing bicycle, with the sighted rider shifting and steering up front while the visually impaired racer stokes from the rear; and then run with the blind athlete, giving them instructions on where to turn and pointing out potentially race-ending obstacles along the way.

At a weekend barbecue in Post Falls to help raise money for the nonprofit organization, they told a reporter that doing one of the races by themselves is one thing; doing it with somebody else is more difficult than it looks.

"I'm concerned about all of it, actually," Birdsall said. "I've never done a swim tied to somebody."

They will have two days to train with their partners before Sunday's race, something that will be important because pedaling a tandem — and keeping it on course — takes practice.

"The first time we ran into a field," Burkhardt said, of his and Birdsall's fledgling foray into riding double.

Burkhardt said he's already talked swim strategy with his partner.

They've decided Burkhardt will swim in front, with his partner trailing just behind. Birdsall's partner, a Chicago attorney, insisted they swim side-by-side, so there is no hint he is being towed.

"The key thing, it's something I wanted to be part of," Burkhardt said. "It's a blessing."