I tried bicycle riding before my run, and still got out of breath after 1.5 miles of my run. I can't breath? I went to the doctor explained my situation. She did some tests and suggested a few things, and told me I have RAD Reactive airway disease. She said my lungs aren't expanding when I exercise. No matter how hard I tried to keep breathing, my lungs just shut me down, my legs wanted to go, but my lungs shut me down hard! She tested me for cardiac problems and found none ( runs on both sides of family, both parents deceased from it ). I have since felt like a new man. I haven't breathed this good since I went to the beach and was in the salt water. Now, I can finally move forward and get started on focusing on my 1st 5k barefoot! The breathing bad was scaring me to death and wearing me out fast! It felt like a heart attack after a run. Going to the doctor was a smart thing for me, just wanted to share my thoughts, maybe it will help someone else figure out there problem?