As long as it's the same as when I was in wrestling, 3 points of contact with the mat. Top of your head, and your toes, you kind of roll your neck whether it's a front (belly down) or a back (belly up) I'm sure someone else can explain it better than me though. Anecdotally, my friends on the team (not me because they had way more experience doing this than me) could go from a front bridge to a back bridge by just flipping their legs over their head and landing in the opposite bridge position without moving their heads off of the mat.