In the world of sex I think there is some truth in the stereo-type that women don't exert as much physical effort as men do (this of course is from the stand point of heterosexual sex). However, as a woman I find that after sex I feel like I've gotten a work out. I wondered how could that be. After some meditation on the subject I figured it out.
Have you ever been in a fist fight where you didn't throw any punches or kicks? If not can you imagine it? You're standing there and someone is punching you again and again. Even though you didn't exert any physical force you're still going to be worn out from the fight. Taking punch of after punch is exhausting. Yeah, so that's what I'm saying. Sex for a woman is like being punched in the vagina again and again. Except it sex feels alot better than a punch in the stomach but the physics is the same.