I always thought that the inner muscles involved in a woman's orgasm was similar to men's. When I cum, my sphincter tightens and it's very much like a Kegel. I always thought women's orgasm was like a strong involuntary set of Kegels. Then I realized that when my fiancee has an orgasm, her lower muscles bear downward, as if she were going to poop. This is exactly 2 opposite directions of contractions. Maybe that's how she is able to squirt really far when she has a strong orgasm. I don't know.