The teacher who told you to "Sit up straight!" had a point. Good sitting posture is important to your health — but holding yourself rigid can be as bad as slouching. Change your sitting posture regularly to alter the forces on your joints and muscles. If you're reading a document or are on the phone, move in your chair, perhaps sit back and relax a little, or stand up to take a call. Here are some more tips on improving your sitting positions.