Take position with your back flat on the ground and feet flat on the floor such that the apex created by your knee forms a right angle. It helps to position your feet under a stationary rail or object to keep them locked flat and so you isolate the abs. Hands may be positioned behind your head, on your forehead or if it feels more comfortable, across the chest. This is the starting position.
Commence the movement by contracting your abdominals and breathing out as you elevate your torso off the floor from the waist. Your torso moves through the arc from the starting position until it is at 90 degrees to the ground.
At the top of the movement, squeeze the abs hard before slowly lowering the body back to the starting position, inhaling as you do.