If anyone gets the chance, you should watch a sleeping baby. They breath so relaxed and so natural. The upper chest does not move, but it is the stomach that comes out on inhalation, and retracts on exhalation. The baby does not yet have any bad "tightening up" habits. Plus, watching a sleeping baby is very good therapy..... And the baby is not thinking about it; He/she just does it. People have mentioned thinking of your belly button touching your spine on the exhale. If that works, great. That feeling can help compress your air, which can help in the upper register. But don't get hung up on it. M.