Shamrock, Yes! Though, I don't agree with Emily65Roses with regard to "to a degree". You can do anything you put your mind and will behind. The only distinction is that you have to take things a little slower and be smarter than most others, and you have to be patient with the results you hope to achieve. I have found it takes much longer to achieve physical results on account of having CF. But I have done everything I have put my mind to. Example, I use to have a FEV1 of 70-75%. Due to the doctors failing to diagnose parasites for over 9 months, my function dropped to 37% with a high of 52%. I was that way for just over two years. The CF Doctors were content on assuming my new base line was 52%. I even had aspergillus (lung fungus-which they said I couldn't get rid of.) It has been a long a difficult (and expensive) road, but today my (FEV1) function is up to 62% and rising. And I arrived here by using nothing but nutritional supplements, vitamins, diet, and exercise. I haven't been on an antibiotic for over 12 months, not even orals, as they were contributing to the strength if the parasites, and funguses. Last month I tested negative (for the second time in 2 months) for aspergillus.
If you want to get in shape, you can. Know this. Just be smart, patient, and take it slow. We have limitations having CF, but who imposes those limitations? And who said we can't exceed those limitations. If you are smart about your diet, consuming nutrients, use antibiotics with discretion, and maintain hope, you'll surprise everyone -yourself most of all. Best of luck.