Simple Push Up(grade)

Every morning (or at least most mornings) I get up and try to immediately do a max number of push-ups and max number of sit-ups.  While doing the push-ups the other day, I stumbled upon an easy upgrade that recruits your core and abdominals more. 

Perform most of the push-up as you normally would- back flat and straight, butt down, core strong.  But instead of keeping your back flat as you raise, raise your butt and curve your back upwards (like a bridge) slightly at the top of the movement.  Imagine a baby trying to crawl underneath you as you are pushing up.  Tighten your core throughout the movement and return your back to a flat (straight) position as you lower.  You should feel a big difference in your complete core.  At least I do.