The act of having sex while the woman holds onto the bedposts and sticks her legs straight out (but with distance between them) while the man hold her body straight out during penetration...resulting in the female being in a superman-flight position.
Bob: "Wow, your sister must work-out."
Tom: "Why do you say that?"
Bob: "We were SuperManing last night for thirty minutes before her legs gave out."
Tom: "Fuck you man."