Do those extreme movements hurt? Are you never in pain?
First, the body has to get used to those movements. You are not starting with the most extreme stretches of contortion when you never have done a simple bridge before. It is a daily step-by-step development, like normal people experience it in yoga lessons for example.
In the beginning, everything feels weird and uncomfortable, but after some lessons your body is capable to breath perfectly and to hold those positions for a while. Since I know my body very well and I’ve been working as a dancer all my life, I can tell how far I can go and how I have to treat it. Sometimes contortion is painful, yes. The brain doesn’t want to leave the comfort zone. But leaving the comfort zone ist he first step in going beyond your own limits.