An exercise ball is a great way to work your core and you can do it right in your living room! A great ab exercise on your ball is the back extension. Once you have positioned the ball under your hips and lower torso, with your knees bent or straight, lift your chest off the ball. When doing this bring your shoulders up until your body is in a straight line. Make sure your abs are pulled in and that you are not hyper extending your back. Repeat this for 14 reps! There are so many exercises you can do on an exercise ball that it is definitely worth the investment!