Tilt the bench and stack extra tension on your abs.
Curl your spine, don't just sit up. Keep the movement in your abs, not your hip flexors.
Setting the bench on a decline puts your abs under load earlier and for longer than a floor crunch, because gravity fights the whole curl instead of just the top few degrees. Your torso also starts from a slightly extended position, letting the abs work through more range on every rep. It is the natural progression when floor crunches stop producing anything but boredom.
They are harder, which for most trained lifters means better. The decline extends the range and keeps tension on longer, so you get more from fewer reps.
Start shallow. Every degree of decline adds resistance, so treat the bench angle like weight on a bar and increase it gradually as sets get easy.
You are sitting up instead of crunching. Curl your ribs toward your hips and stop once your abs are fully shortened. Coming all the way up to vertical hands the work to your hip flexors.
