That's interesting. Have you talked to your doctor about it? I had never been diagnosed with asthma but had allergies for a long time. I didn't recall having any big issues, but then I went on a bike ride across Iowa. Riding 5 or 6 hours a day just about did me in. At the end of the day, I couldn't stop coughing and in the morning, my lungs were so congested. I had no idea what was going on but went to the doctor afterward and was diagnosed with exercise-induced asthma. I just have to use an inhaler before rigorous or long training sessions. Moderate exercise usually doesn't bother me.
Unfortunately, it's gotten progressively worse and I've had pneumonia twice. I'm pretty good most of the time, but a virus can wipe me out. I definitely can't exercise in the cold. I have trouble just walking if I don't have a scarf over my face.
I would just talk to your doctor about it. A rescue inhaler would be good to have around if you do have some issues. If it's mild, you don't have to take a lot of meds or anything. I can't handle strong chemical fumes and have to use green cleaners and avoid a lot of dust or pet dander.