I did the same 25y ago, as prescribed by my allergy doctor. It was called (translation from French) "breathing reeducation", and it was roughly interval training: breathe fully in through your nose, then blow into a pipe (connected to a spirometer) at various speeds.
Before that, I was mostly breathing through my mouth. It was challenging even to eat a sandwich while walking :). Since this reeducation, I only breathe through my nose with no effort. I'm willing to believe it indeed has to do with muscle.
Before that, I was mostly breathing through my mouth. It was challenging even to eat a sandwich while walking :). Since this reeducation, I only breathe through my nose with no effort. I'm willing to believe it indeed has to do with muscle.