How does peak flow change during exercise?

When people say it's 'Deepness of Breathing' ..how does that change in scientific terms during and after exercise?

What affects our Peakflow?

I don't really understand it.

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Answer:
Peak flow measures the amount of oxygen you can push out of your lungs. If you exercise, (and are asthmatic) your airways will probably be sensitive to the physical exertion. Therefore, they will tighten a little, thus, lessening the amount of O2 you can release from your lungs.