This stability ball exercise really engages your butt for a belfie-ready rear end.

Step 1: Lie on the floor with your lower legs on an exercise ball. Extend your arms out to your sides.

Step 2: Straighten your lower back, knees and hips, raising your back and hips off of the floor.

Step 3: Keeping your hips and lower back straight, lower your knees, pulling your heels toward your rear end. (Allow your feet to roll up onto ball.)

Step 4: Lower to your starting position by straightening your knees.