Simon,
A month before my medical my peak flow was 600, did plenty of excersize and looked after my diet and at the medical my peak flow was 650 which they said was very good.
40 minute workout in gym 4 times a week (get your gym to give you a programme). And consumed nearly zero dairy in my diet to keep asthma at bay.
HJ
Edit for Tommy, I take those inhalers and attended the Mater and they never even asked what inhalers i use. Get your GP to write a letter confirming what you are saying and you should have no problems