Here is an easy way to tone your abs while sitting at your desk at home or at the office. Sit up straight in a sturdy chair with your feet flat on the floor. Keep the knees together, back straight with upper back resting on the back of the chair, belly pulled in and your palms wrapped around the front edge of the chair. While supporting yourself with your hands raise your knees up toward your chest. At the same time lean the chest in toward the knees and exhale. Hold for a count of 5 and return to the starting position. Do this 3-5 times to start and build up 5-8 times.