If there's one thing summer movies promise, it's excess. You're almost guaranteed to see lots of action, lots of explosions, lots of skin, and lots of muscle. But the latter doesn't develop overnight. In fact, what you don't see are the hours of prep work these actors put into getting their bodies box-office ready. Want to know what it really takes to develop an action-ready physique? Here's how to get fit like seven of this summer's hottest stars.