Chasing Stronger, Defined Abs?

ABS - Elbow Plank

Take position on the ground as if you were setting up for a push-up only your weight is held up on your elbows instead of the outstretched hands in the push-up. The upper arms should be perpendicular to the floor lifting the torso up; your forearms resting flat on the ground. You should be up on your toes and with your body flat, not arched either way. This is the starting position.
Hold this position for the prescribed duration, keeping your core tight and remembering to breathe normally.