Unless the sex we’re talking about is of the one-night-stand, where-are-my-pants variety (in which case your biggest worry is oversleeping and missing the race entirely), science doesn’t have much to say about your pre-race behavior in bed. Neither do the pros: Muhammed Ali famously abstained from sex before a fight; Oscar De La Hoya and Manny Pacquiao have been said to follow suit. On the other hand, Olympic swimmers Ryan Lotche and Federica Pellegrini have made clear that they have no such beliefs, and No. 1-ranked female MMA fighter Ronda Rousey said last year that she tries to have as much sex as possible before a fight because “for girls, it raises your testosterone.”
Even ancient history has its conflicting opinions: In 444 B.C., the philosopher Plato said that “Olympic competitors before races should avoid sexual intimacy." In 77 A.D., however, Pliny the Elder wrote that "athletes when sluggish are revitalized by lovemaking."
So what does the research say? A 1992 study from Georgia State University researchers backs up Rousey’s claim that sex does indeed increase testosterone levels, for females as well as men—although it’s unclear whether the change would be enough to offer a performance advantage. An editorial published in 2000 suggested that “sex the night before competition does not alter physiological testing results,” based on the results of three previous studies. However, the psychological effects of knocking boots have not been studied or proven, editorial author Ian Shrier, professor of epidemiology at McGill University in Montreal, told National Geographic News in 2006. In other words, there’s no knowing whether sex will mess with your mindset or concentration the next day, either negatively or positively.
In lieu of definitive advice, I’d stick with the old training mantra: “Nothing new on race day.” If a little bit of premature celebrating is part of your regular routine, by all means, have at it. But if you think it has the potential to keep you up all night, wear you out, or distract you from your goals the next morning, save it for the victory party.