Obesity does not "displace" air, it restricts the diaphragms ability to drop. You need this expansion to open the terminal air sacs in the lung. There are many many of these in clusters that when added up has more surface area than any volume displacement could come close to matching. If you are a thin person and don't take in deep breaths, the same thing will happen. Using the exercises I mentioned above will open much more of these airways whether you are thin or obese. The factual physics (physiology) behind the Gmonady Raw of Power.