I did that with my second baby. basically instead of pushing with each contraction/urge to push, you breathe instead. You know how when they tell you to pant as the head is being born? Like that only you do it the whole time. I had a very quick second stage with her as she descended very quickly and they didn't want her to be born too fast (not sure why, I assumed due to the change in pressure from being in the birth canal to being outside it) and I tell you what, it was harder to do that than it was to actually push because you have to fight the urge to give a good hard push with every inch of your body because it is such a strong and primitive thing to do. You know yourself that the urge to push is strong and uncontrollable and this is basically going against what your body wants to do.