i think some do some dont, also i think its mostly like the last week or two before a fight...
dont ask me why, if i had to say what i thought it was think i would say it was like a sort of fire in your belly.... like i know of a few musicians that wouldnt have sex while recording an album cos they feel its like a creativity inside or like a fire inside if you like, go and have sex you blow it?
not quite sure how it works in boxing .. but i sort of can imagine it!
lol peace