It's Iditarod season, and Outside magazine turns its focus from human-powered recreation to the amazing athletic capabilities of Alaska's racing sled dogs -- and how they might hold clues to improving human performance. The Pentagon is funding some of the research in hopes of training superfit soldiers for special ops. Continued on jump

"When it comes down to sheer capacity for prolonged exercise," says Ken Hinchcliff, an Australian veterinary physiologist who's done more research on sled dogs than any other scientist, "there is no other animal, including humans, that comes close to competing."

Outside's Brian Alexander visits the Fairbanks-area kennel of Aliy Zirkle and Allen Moore -- and focuses on a dog named Tony -- to learn what's known so far about sled dog stamina, and what's not known.

If a man performed anything close to such extreme exercise, he'd have to recruit every drop of blood his body could muster, sending it through the lungs and to the muscles. That blood would be rerouted from other organs, such as the kidneys, the liver and the gut. But that requires those organs to virtually shut down, which you can do for only so long before you start to damage them.