Jackknife Pushup

Set your hands on the floor as if you were going to perform a wide-grip pushup. Now walk your feet up toward your hands so that you are in a jackknife position with your hips at the highest point and your torso almost completely inverted. Keep your head in a neutral position and lower your body until your head touches the floor, then drive up back to the starting position.

This exercise has several levels of difficulty: the first is with feet on the floor; the next is to place your feet up on a bench; and the third is to place your feet on an unstable surface such as a Swiss ball.