BOULDER – After riding 674 miles in six days, Tom Danielson was nonchalant. He had just crossed the finish line, ending Day 6 of the USA Pro Challenge.

He had climbed Flagstaff Mountain, a daunting challenge on this day with a blazing sun, but that’s been his life all week. He’s also conquered Independence Pass (twice), Hoosier Pass and Cottonwood Pass, among others. He’s climbed 42,000 feet.

He shrugged. It’s no big deal to him.

“I’m pretty used to it, you know,” Danielson said.

I’m not sure I ever will get used to it. The cyclists in multistage competitions compete in a marathon and then turn around to compete in another marathon the next day. This is, I know, an inexact comparison. Cycling doesn’t punish the body the way running does.

But think of it: A cyclist in this Challenge has been forced to struggle with a collection of the world’s finest, fittest competitors. A cyclist has been forced to compete against altitude, which requires a complex blend of courage and wisdom.

Pity the cyclist who ignores the perils of altitude.

Mountain runner Matt Carpenter, who lives in Manitou Springs, knows all about the vicious kick altitude can deliver to the too-bold athlete.

“It’s like somebody is basically doing a Darth Vader on your neck and turning off the air,” Carpenter said.

There were a few times Saturday when I wondered if Darth Vader would invade the race.

A large chunk of the population of greater Boulder showed up to watch the competition and it was impossible to avoid watching the goofs who dressed up as Hunter Thompson (complete with cigarette holder), a Star Wars storm trooper, bumblebees and super heroes. Dozens of spectators raced beside the cyclists as they rode up Flagstaff. These spectators were howling, waving flags, playing to the camera.

For some, I suspect, the spectators delivered an entertaining show. For me, all the weirdness served as an unfortunate distraction. In football or basketball or baseball, we don’t suffer through the endless intrusion of those watching the event.

And this event is special. These cyclists are amazing athletes. Superhuman, really. I realize I’m gushing here, but there’s good reason for admiration.

After riding 117.9 miles from Breckenridge to Colorado Springs on Friday, the cyclists arose Saturday morning to ride 102.8 miles in a looping route from Golden to Boulder. They will arise one final time Sunday to ride in a 9.5-mile time trial on a flat, fast course through the heart of Denver.

Ron Kiefel, a Colorado native, competed seven times in the Tour de France in the 1980s and 1990s. He’s served as a VIP driver during the Cycling Challenge. He kept a close eye on the road and on the cyclists while remembering the thrills – and the agony – of his career.

How is it possible to ride at top speeds while battling altitude day after day?

Kiefel laughed.

“You have to be really good at suffering,” he said. “It’s amazing how much harder you can go than you ever thought possible.”

The cyclists don’t enjoy talking about the extreme challenges of their sport. This is their life. They look at a fast ride through the mountains as just another day at work. They’ve been preparing for these challenges for years.

“It’s a very long, gradual process,” Tyler Farrar said. “I’ve been riding since I was 12 years old.”

Farrar said cyclists take “baby steps” until they are finally ready to ride up and down mountains, day after day, week after week.

“It seems crazy to someone who hasn’t gone through the process,” he said.

He’s right. It does seem a little crazy.

But even more inspiring.

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