My asthma wasn't that bad to start but would still cause me issues when I was running hard like chest tightness and wheezing which linked directly into a drop in performance. I'm not a bad runner so I'd go from 5:30 mile pace in a race and end up doing over 6 even though my legs were fine just unable to get the air in.
I take an inhaler in the morning and at night and take my ventolin before I do any hard training or racing and touch wood my chest has been spot on. I only know its working as I forgot to take it for the club handicap and my performance dropped dramatically all in the space of 100m when my chest tightened up.
I do regular peak flows and prior to exercise it was up around 510 then post exercise would drop to 480-500 which is a significant drop. Now I take the inhaler its increased to 520-540 prior to exercise and maintains immediately post exercise.
Peak flow should increase or remain the smae post exercise if it does drop it shows that you are getting a restrictive pattern in your lungs which will be due mainly to bronchoconstiction.
The inhaler I take in the morning and night is a mix of a corticosteroid and a long acting bronchodilator. The corticosteroid to reduce airway inflamation and the long acting bronchodilator to keep the airways open. In theory the one I take lasts for 12 hours. These include medications such as seretide and symbicort (a COPD inhaler but it works for me). The Ventolin I only take prior to hard exercise this really as a preventative measure so that the airways are even less likely to go into spasm.
What tends to happen is you'll get put onto ventolin which is about 2 quid a metered dose inhaler as its cheaper. The corticosteroid that you'll generally be thrust is a brown one which be becotide or beclamethasone which at the most is 8 quid. Most medication is given as its cheap even though its not always the most effective. ie symbicort is 30 odd quid an inhaler and seretide the same.
Its also important to have you asthma controlled as uncontrolled asthma is a precursor to COPD not what you want. I only know this as part of my role as a physio is with COPD patients and god its scary at times