An interesting article on MSNBC this morning about sled dogs and their athletic abilities.
http://www.msnbc.msn.com/id/26889282/
Here is a few paraghaphs about physiology:
Probing deeper into the dog's physiology, they made three other determinations, which will be outlined in a presentation at this week's American Physiological Society conference in South Carolina.
First, they found that the dogs rapidly adapt to sustained, strenuous exercise. Four days into the Iditarod, the dogs' biochemical profile returns to where it was before the race began, as though nothing had happened. Elite human athletes, in contrast, show signs of fatigue after continuous exercise and require recovery time.
Second, Iditarod dogs possess an enormous aerobic capacity, which refers to the ratio of volume of oxygen to body weight per minute. A fully conditioned sled dog's aerobic capacity is twice that of an untrained sled dog.
Finally, each approximately 55-pound sled dog can burn up to 12,000 kilocalories per day, which is the equivalent of 24 McDonald's Big Macs. A human would have to consume and efficiently process the equivalent of 72 Big Macs to fuel a day's Iditarod run.
I see a new training technique on the horizon for marathoners.