Is it time to start taping up my mouth during runs and develop a nasal breath during exercise? Interesting thoughts here from Patrick McKeown promoting nasal breath to enhance physical performance.
Taken from the excellent book of the same name, the Oxygen Advantage would argue that nasal breathing limits the amount of air going into the lungs and that over time your body will adapt to need less air. It also increases oxygen uptake and the amount of oxygen going into the the cells, since CO2 levels have proven to be higher when breathing through the nose. The more CO2 there is, the more oxygen the red blood cells release.
Go dig the book out if you've not already.