Okay, guess who I'm impersonating. "Oh hi, I make high-pitched noises and love running for hours and hours but going nowhere." If you guessed your anorexic neighbor with the home treadmill, you're wrong, but close, because why wouldn't hamsters have a bad body image: they're chubby fuzzballs. But on some real talk, hamsters (and gerbils, mice, and rats) are all about running in wheels.
Now we humans could run in a wheel, but we don't, because there's nowhere to put the mileage and calorie calculators, and if you can't figure out how many Snicker's bars you burned off, why would you ever do anything athletic? Not to mention that although treadmills, stationary bikes, and ellipticals look ridiculous, gigantic wheels would look even worse. Plus, you'd have to attach them to the wall, and then how would people stare at themselves in all the wall-length mirrors? Nope, our pet rodents definitely have this one all to themselves.
(flickr photo Abe running in his wheel by Stoichiometry; http://www.flickr.com/photos/stoichiometry/2266389862/)