I always hated it when teachers would tell me to breath through my nose. My sinuses suck, and its just hard. Why should I. Is mouth breathing so faux-pas? Do I have bad breath?
Turns out, the fitness teachers weren't just being obnoxious, just obtuse. Maybe they had no idea either.
Breathing through your nose makes the oxygen reach your blood stream faster. Thereby oxygenating your muscles you are trying to work and stretch. Making the workout easier and less likely to get injured. Breathing out through the nose also rids the bad air faster.
Huh.. who knew?