I am in excellent shape and have no "breathing" problems outside of sports, but one wouldn't think so listening to me swim, bike, and run, I huff and puff my way through, even practicing breathing excers. I breathe so heavy you can hear me a mile away, but I am actually NOT that tired, and don't FEEL like I am gonna collapse or drown, so I have stopped worrying about it. At the pool the lifeguards come and ask if I am ok,(until they get to know me), when I am riding up hill, people turn around to see who is breathing so hard as I come up to pass, and running, even slow-ish, I breathe heavy. Just decided that some people breathe heavier, just like some people are more flexible.