Yoga balls, also known as stability or exercise balls, are a great way to add variety to your muscle conditioning routine. A yoga ball can be used to support your back when you are doing abdominal exercises. You can also sit on the ball, using it like a chair, when you are doing upper body (arms and back) exercises with weights. When doing muscle exercises for the upper body, the yoga ball keeps your core muscles (middle body) working hard. You can even use the yoga ball for different stretches for your back and abs. Make sure you receive proper instruction on your form from a fitness instructor or coach before trying the yoga ball.