Deep breathing - really forced deep breathing - while running I found best for lung capacity.
Whatever you do, increase your efforts over a period of time, not like a bull in a china shop.
I was really sickly at school. Excused all sports, but when I discovered judo, and indeed tennis, wanting to do it made all the symptoms go away. People call that, 'growing out of it'. I expect much of it is in the mind when it comes to sudden reaction asthma.
I've often wondered if straining to exhale for (about 40 minute periods each attack) caused my breathing to gain some kind of advantage. By the time I was doing my medical on the old iron machine at the CME - I was nearly pushing the pen off the scale.
Typically 740 over the years, but now, I occasionally get restricted breathing, and I don't know why. It seems people that got asthma when they were kids can find they get it when they get old. Odd that.
I do the same. Use a puffer to open things up, and then really go into aerobics - forcing air in deeply. Seems to work. GP very surprised I got back to a 720 from a tiresome 550.
These simple machine readings are almost unbelievably consistent. Even the plastic take-home ones seem to agree to + - 5 In fact, I think the guys at Praed St, the old CME, were up to mischief. Several of them had me blowing for about half a dozen tests, and my guess is they were trying to make me the first person to blow the pen off the disc. However, the peak was almost - to the thickness of the line - exactly the same. Some of these old bits of kit were very nifty.