Something that I've realised recently - breathing in sync with your pump movements, improves pumping. Breathe out on the sail pull and breathe in whilst moving the sail forward.
There are a few good videos out there for windfoil pumping techniques. They focus on the movement, but don't generally mention breathing.
I've noticed in the last few weeks that my breathing during pumping is not controlled, and that can lead to being out of breath after hard pumping onto the foil. Sometimes I would hold my breath momentarily during the start of a hard pump, which affected how long I could sustain vigorous pumping. Breathing in sync with the pumps has meant that I'm less tired after getting up on the foil and can pump harder and longer.
Try it next time you're out on the water and let me know if it helps 
I rarely pump the sail, but when things get fast with interesting wave patterns sometimes I notice I am not breathing properly, a thrill a second can take your breath away!
