If you want to work out your abdominal muscles, it is possible to do right from your own desk. To do seated crunches, make your sure feet are lying flat on the floor with your knees bent and you’re sitting up straight. To make sure you have good posture, adjust your chair so that it sits straight up and lean against the back. Keep your hands in your lap and take a deep breath. Every time you release your breath, push the lower part of your back against the chair as you tighten your abdominal muscles. You will feel a burn in your upper and lower muscles after several repetitions.