I have to go with Irishpower and Jay on this one. I have had sex before fights, and before lifting, and I have also fought without having had sex and have lifted without having had sex. It makes no difference. If you are so out of shape that a little nookie the night before a performance is going to knock you off your level, then you need to be in better condition.
I have sex as often as I possibly can. If I did not, there would be a lot of injured and dying people around me. And incidentally, guys for your prostate's health, it is important to "release" as Jay put it, every single day. I never miss a day and neither should you. You prostate will thank you for it in a few years.
B.