The epi-no can be used during pg for pelvic floor. It basically gives you something to squeeze down on, and you read the pressure on a guage so you can see if you're getting stronger, and making sure you're holding the same pressure for the 10 sec or however long you hold it. It's used for these exercises as well as inflating the balloon for the perineum.

Just as a note.. my butt muscles squeeze whenever I do it too, but then I'm able to sort of move the squeeze further forward... if that makes sense! LOL.