A few months ago I was experiencing shortness of breath - I just felt like I couldn't fill my lungs to capacity unless I yawned or really tried, so I was yawning all day and constantly feeling like I couldn't breathe. I went to the doctor, they ran a bunch of tests, all said "everything's good!" but breathing was still rough. I had put exercise on hold because of it, but with doctors saying I had no issues, I figured "meh, might as well try again". Trying again was exactly what I needed to do, because a couple months later I no longer am feeling that symptom and my lungs feel awesome. I don't know if it was my lungs physically needing to be challenged, or if it was stress induced and exercise helped that, but I can absolutely say that exercising has greatly helped my breathing.