If you think running a marathon is a feat in itself, imagine doing an ultra-marathon up a mountain. At “The Rut Mountain Race” in Big Sky, Montana, nearly 400 athletes from around the world gathered to compete across 31 miles. They cover more than 10,000 feet of elevation. The sport is known as “skyrunning.”

As part of the “CBS This Morning” series, “Pushing the Limits,” we take a look at the world’s elite athletes who are getting their high-altitude adrenaline rush.

Luke Nelson sums it up when he says:

“I run in the mountains because it gives me a freedom that I can’t find anywhere else…. I think the human body was meant to run; but this is pushing it!”

View the film here

http://www.cbsnews.com/videos/pushing-the-limits-skyrunning/?tag=facebook

You can read reports and view images from RUNTHERUT races below:

VK HERE

SKY HERE

ULTRA HERE