http://swissbaync5d7ykaz7dh7v4qjrb4gmen5aj3bogxrcgbb43ij34bjuyd.onion/pdf/Books/Survival/Medicine/oddsnends.htm
Although you cannot remain under as long with empty lungs as with full, because
you have no air to exhale as sort of last-gasp reserve, you save strength and avoid water
disturbances because you have no buoyancy to struggle against.