The 3-part rolldown is a slow and controlled movement for core strength. It is similar to a crunch, but emphasizes the lowering movement.
Sit on the floor with your knees bent and hands behind your head. Hook your feet underneath a bench or couch.
Do a Situp so that your abdomen is near your thighs. Slowly roll back in three parts. First, place your lower back on the ground. Then, place your mid-back on the ground. Finally, place your upper back on the ground.
Avoid rounding your upper back. Keep your chest up and shoulders back.
Don't sway from side to side. Focus on controlling the movement.
Don't forget to keep your abs contracted as you lower your body. Stay tight.