This version of a decline crunch isolates the oblique muscles of the abs.
Steps
Lie on a decline bench face up. Place your feet securely under the pads. Place your hands either across your chest or on either side of your head (over your ears).
Raise your shoulders and chest up keeping your back straight and bring your left elbow to your right knee, slowly crunching your abs.
Pause for a moment and then return to the starting position. Lay fully back and repeat with your right elbow to your left knee.