Using a decline bench, position yourself with your feet locked in at the top.
Place your hands on either side of your head, without locking your fingers.
Raise your body slowly while you contract your abs.
Crunch up, bringing your elbows to either side of your thighs.
At the top of the movement, flex your abs for a one-count and then slowly lower your body back to the starting position.
Be sure to keep at least an inch or two of space between your back and the bench at the bottom of the movement.
Also, for added muscle building, hold a weight plate across your chest for added resistance.