If someone left a treadmill in your living room, how far would you run every day just because you felt like you had some energy to burn? Five miles? Zero miles, and you'd use it as a tie rack? How about 65 miles?
Researchers at the University of Pennsylvania and elsewhere studied mutant mice that were missing a particular gene involved in cell signaling. They thought the gene had something to do with muscle development, and sure enough, they found that these mice had some pretty definite abnormalities in their muscles. For example, when an exercise wheel was put in their cages, the mice ran and ran. The wheels were rigged to devices that counted the number of spins they took, and the researchers converted that number to a distance. They found that during just one night (the active period for mice), mutant mice ran an average of 5.4 kilometers ...
