There are meditation techniques that utilize the "inhale-nose/exhale-mouth" rhythm. There are also athletic trainers who recommend this method, I think, tho' I've only heard that from friends. The nose/mouth method was supposed to get deeper, controlled inhales, and faster exhales, to improve your control under high exertion. Definitive studies? Don't have 'em, so don't take my word for it. For the most part, though, I find myself doing this method method anyway, and I bring myself back to it when I'm pushing it.