Decline Crunch
Depending on the bench setup, either sit with your buttocks at the top angle of the decline bench (angled at 15-30 degrees) and position your feet under the ankle rolls OR if no ankle rolls exist, simply slot your feet under the knee rolls with your torso positioned lower down on the bench.
Slowly lower your torso backwards onto the bench until it is flat. Position your hands behind your head or if it feels more comfortable, you may instead cross the arms on the chest. This is the starting position.
Commence the movement by contracting your abdominals and breathing out as you lift your shoulders off the bench to the maximum height you can squeeze to. As you lift your body, your lower back should remain in contact with the bench. This contact remaining is what limits the height your shoulders achieve.
At the top of the movement, squeeze the abs hard before slowly lowering the body back to the starting position, inhaling as you do.