Think of this exercise as a push-up that's mostly for your shoulders instead of your chest. It forces the shoulders to work hard to drive your body back using a natural arc and push angle.
The Push-Back Push-Up
Level 1: Drop down, explode straight back, and return to push-up position.
Level 2: Same basic movement, but put your feet up on a braced bench. Your abs will be screaming.
"Back in the days of being 297 pounds, every workout was brutal; there was no other alternative. That's not the case any more. Have I become soft, like a former all-star playing out a multi-million dollar contract?"