It takes training. There used to be a video uploaded to an amateur porn site offering tips, such as: how to relax, arch one’s back, and stick one’s ass out at the same time, to throw the head back, like a horse, but sexy. To grab the arm of one’s partner (who needs something as support, so just one, or they will fall over) and pin it behind the back. To focus on consistency of rhythm and balance that against variation, how to speed up and slow down. It was by a semi-professional, self-employed making enough on selling clips to be full time gig. It takes dedication to commit to that sort of production value.