The sexual "workout" after working out is a common theme in porno. Supposedly women get so hot and bothered while working out they can't control themselves anymore and fuck the first gym member they see.
I have a couple problems with this setup. There are no attractive ladies at the gym I go to. If you're really getting a good workout, not only are you going to work up a good stinky sweat, you're also going to be quite tired. After my typical workout I don't think I'd even be interested in the hottie Lisa Ann. And she sure wouldn't be digging my sweaty stank ...