In 1997, Navy SEAL Randy Hetrick was deployed in Southeast Asia, where he was stationed in a remote warehouse for weeks with no way to exercise. So he grabbed an old jujitsu belt, threw it over a door, and started doing pull-ups. Today, TRX exercise straps dangle from the ceiling in gyms across the country and are standard workout gear for professional athletes. PLUS in our postscript "How You Built That," how Whitney Sokol created SproutFit — adjustable onesies and leggings that grow with your baby.