Write an article based on this "Sit down on the fitness ball. Check for proper compression. Check a sizing chart."
Distribute your weight evenly and keep your feet flat on the floor. If the ball’s the right size for you, your hips and knees should both be bent at about 90 degrees, and your thighs should be horizontal. Your upper body should be vertical with your ears, shoulders and pelvis aligned. Don’t lean in any direction to avoid creating a counterbalance. It's not enough for the ball to fit your body; it also needs to be properly inflated. A properly inflated fitness ball should compress about 6 inches when you sit on it.  If the ball fits your body but compresses more than 6 inches beneath you, it's not the right size ball for you; it's a larger ball that's been under-inflated. You can exercise on such a ball, but may find that the extra-soft ball feels awkward and makes balancing too easy. Don't over-inflate a smaller ball to make it fit your body; the extra pressure makes it more likely to burst. When fully inflated, you should be able to press 2” into the fitness ball with your finger. Fitness balls lose pressure with use and age. As your ball ages, you may need to inflate it more often. Manufacturers provide fitness ball sizing charts that correlate ball diameter with body height. These are only estimates and vary widely between the various ball manufacturers. Give how the ball actually fits your body higher priority than the sizing charts. You may be able to successfully use a smaller or larger sized fitness ball as you gain experience.