I had this feeling again after a ride this week and decided to go to the dr. to see what was up. She suggested I had exercise induced asthma, and gave me an inhaler (Proventil) to use 20 min before cycling. Two other tests she did on me were negative. I tried the inhaler and felt much better after my rides. This only happens when my heart rate gets really high. I researched this on the Net and found that this is really common in athletes and will possibly go away with conditioning. That is what I am aiming for! I absolutely hate to take medicine, but will do it when necessary.