If you're determined to keep your abdominals firm and flat, here is an excellent move that takes very little time but delivers big results. It requires you to keep your lower body still while recruiting your abdominal muscles to move your upper body. But as effective as this exercise is, it's important to remember to use your abdominals all day long. Make it a habit to stand tall and pull your navel toward your spine. This will train your ab muscles to stay active and strong even when you're not at the gym.
1 Lie on your back on a padded surface or a mat. Bend your left knee, foot flat on the floor, with your right leg extended up. Hold a stability ball between your right leg and left knee and place your hands behind your head to support your neck. On an exhale, without moving your legs, contract your abdominals and raise your left shoulder toward your right inner thigh. Pause at the peak of the contraction for a moment, then lower to the start position. Repeat eight times.