Built for speed...

Or, at least, for running. A variety of evidence--from how we cool our bodies to the length of our toes--suggests that humans evolved for long distance running.

So why so many injuries? More and more people think it may be due to our thickly padded running shoes... another example of unintended consequences. I know when I tried running barefoot a summer ago that I felt a lot less fatigued, though I needed to do some stretching to compensate for being used to running with a thick-heeled shoe.