Using a fitness ball? Pick the right size

By Mayo Clinic Staff

Fitness balls come in various sizes. For most exercises, you'll want a ball that allows your knees to be at a right angle when you sit on the ball with your feet on the floor. The firmer the ball, the more difficult the exercise will be. So if you're just starting out, you might want to slightly deflate the ball. You can add more air as you gain strength and confidence.

Nov. 12, 2011 See more In-depth