With regular exercise I have improved my peak flow from 300 to 400, 33% improvement. If nothing else that benefit is worth the effort. So any other asthmatics out there, please be encouraged. I am now just touching the normal range for my age and height. I can really feel a difference.
That is brilliant Rowan... being an asthmatic myself (and yes embarrassingly a smoker) I walk pretty much everywhere to keep oneself fit... my football days are gone-ish ;-) with my peak flow meter it reads a bout 550+ I had a check-up last week+ flu jab. Even though I look after a lot of animals etc... to me it is the exercise however, shape, or form... that keeps one a little fitter.
It's not quite the same for chronic asthma. Exercise does help a bit, but doesn't give spectacular results. My maximum peak flow is about 220. After 45 years with chronic asthma I have lung damage which can't be reversed, so the amount of effective exercise I can do is fairly limited.
It's good for depression too. I used to drag a friend out on walks every day when he was struggling. I knew he was getting better when he stopped fighting me and was waiting for me to arrive. I hated it, I don't do exercise but friends are important.