Secure your legs at the end of the decline bench and lie down.
Now place your hands lightly on either side of your head keeping your elbows in. Tip: Don't lock your fingers behind your head.
While pushing the small of your back down in the bench to better isolate your abdominal muscles, begin to roll your shoulders off it.
Continue to push down as hard as you can with your lower back as you contract your abdominals and exhale. Your shoulders should come up off the bench only about four inches, and your lower back should remain on the bench. At the top of the movement, contract your abdominals hard and keep the contraction for a second. Tip: Focus on slow, controlled movement - don't cheat yourself by using momentum.
After the one second contraction, begin to come down slowly again to the starting position as you inhale.
Repeat for the recommended amount of repetitions.
Variations: There are many variations for the crunch. You can perform the exercise with weights, or on top of an exercise ball or on a flat bench.