The reverse crunch comes in 7th place for effective ab exercises, with a focus on the rectus abdominis. With this move, you're curling the hips off the floor, so you'll feel this in the lower part of the abs. The key to this move is to avoid swinging the legs to raise the hips. This is a small, subtle move, so you only need to lift your hips a few inches off the floor. Follow these steps to do reverse crunches correctly.