The reverse crunch is a highly effective exercise for targeting the abs, but it is often overlooked by many. To perform the reverse crunch, simply lie down on the floor or a mat. For a greater challenge, keep your feet off the ground throughout the exercise. This will maintain tension in your abs for the entire duration. Be sure to avoid using momentum when lifting your legs and refrain from arching your back. The reverse crunch primarily targets the rectus abdominis, or six-pack muscle. It is recommended to do 3 sets of 12-20 reps as part of your core training routine.