An ab roller is a fitness tool used to strengthen the core abdominal muscles. It consists of a wheel with handles that rolls in both directions, requiring the user to push and pull the device while keeping the body balanced. An ab roller can be used to target different areas of the abdominals depending on the way it is used. The most common exercise with an ab roller is the roll-out, which involves rolling out from a straight arm plank position and then back in to the starting position. This exercise works the entire core, including the rectus abdominus, obliques, and transverse abdominus.