As a fellow asthma sufferer, I, too, have pondered this question.
Asthma, of course, is more about the airways leading to the lungs -the bronchials- than the lungs themselves. The airways constrict from irritation -and that can come from many, many causes- and air can't get *to* the lungs. the lungs are fine but they're starving, for want of a better image. I can trigger an attack if I laugh too hard for too long. That's why I'm such a crank, I can't afford to laugh
But I thought if I kept riding, I'd have to improve. I also get allergy shots every 3 weeks and, because of my asthma -and the fact that I'm only working on about 60-70% of normal lung capacity, at best- I have to huff into the peak flow meter and "pass the test" before they'll give me my shots. In the year and a half that I've been doing this, my peak flow hasn't changed appreciably at all. Still 60-70%, give or take. Depressing, ain't it?