As y'all are well aware, I hate being controversial. But still. Theories have to be given their turn in the spotlight. So.
Two things men think with: one, everyone knows, well established fact and whatnot. Two, their feet. This is why (one figures) men don't normally think about much when they run (except hot chicks if they see any - which further proves theory and acts as corollary). And this is also why, conversely, women think a lot when they run. Cos women use only their brains to think.
What dya guys think? Do I have bases covered?