I know nothing of cystic fibrosis honestly. I wish I could help more in that area.
But as far as lung function I would think any good arobic activity might help. Like I said I dont know enough about your disease to know what is ok and what isnt for it so obviously I could be wrong. Do you swim at all? Swimming is one of the best workouts in my opinion. I spent the other afternoon in the pool and I was out of breath by the end of the day and the next day I was so very sore. Great workout. Sorry I wish I could help more, I just wanted to answer your post because no one else had..let me know more about your disease and maybe I can help more.