During your squatting routine, be sure to engage your abs. What does this mean? Essentially, you need to tighten your stomach muscles -- from upper to lower. You can easily achieve this by clenching those muscles (be sure you can still breathe properly) before you begin the downward motion of the squat. Keep your abs flexed, since you'll need their help on your ascent from the squat. Without proper ab assistance, you can run the risk of shoulder, leg, or back damage. Release your abs as you take a fresh breath and start a new repetition.