Abstaining from sex is a weird thing athletes do.

On Saturday night, two first-rate athletes will go toe-to-toe in Las Vegas — both incredible fighters, but only one that’s getting laid. Floyd Mayweather Jr., an undefeated five-division world champion boxer, has publicly admitted that he plans to abstain from sex until after his much-hyped fight against UFC lightweight champion Conor McGregor. The Irish mixed-martial artist, meanwhile, famously said in 2015 that before fights, he likes to “have as much sex as possible.”

While Mayweather’s choice to not get freaky until after the match is a decision rooted in Rocky movies and ancient Greek lore, it’s not exactly backed by science. In a systematic review of studies published in Frontiers in Physiology in 2016, an international team of researchers writes that the scant evidence available on the subject suggests there’s no direct impact of sexual activity on athletic and strength performance.

“This aspect [sex] is considered important in sports, but there is insufficient evidence of the possible specific detrimental effect on the sports performance,” the researchers write. “In addition, no exhaustive data are available about the possible impact of the sexual activity on different kinds of sports, in terms of endurance or resistance performance.”

Floyd Mayweather Jr.

The researchers originally began with 130 studies and then culled that number down to nine, after realizing the work of the others wasn’t sound. In the remaining studies, there was no evidence stating that abstaining from sex would benefit an athletic performance.

They did find two potential downsides linked to having sex before a feat of athleticism: One was that sex is sometimes paired with other unhealthy behaviors, like smoking or drinking, which could affect athletic ability. In addition, they point out that “at least a few hours should pass between sexual intercourse and sports competition.” People only have so much energy.

What he doesn't want to do is sex.

Despite this lack of scientific proof, many athletic coaches spread the myth that sexual frustration will lead to increased aggression and that ejaculation will draw away needed testosterone from the body, the researchers write, pointing out that none of the studies they looked at showed that sex caused noticeable changes in testosterone levels. Even if testosterone levels did fall prior to an athletic match, it probably wouldn’t matter: Studies have shown that, while testosterone injections increase and strengthen muscles, they don’t instantly affect athletic performance.

“A long-term buildup of testosterone would produce results,” Allan Mazur, a professor of public affairs at Syracuse University, told The New York Times in 2006. “But we don’t know the short-term effects of using testosterone on an athlete’s performance, or whether it even has a short-term effect at all.”

That may not be true.

There’s no evidence to show that sexual frustration will increase aggression, but science does support the idea that sexual frustration can give you blue balls. Technically known as epididymal hypertension, “blue balls” is what happens when blood is retained in a male’s genitals after prolonged sexual arousal. If Mayweather really isn’t having sex until after the fight, he might want to steer clear from anything that gets him in the mood.

Photos via Getty Images / Al Bello, Giphy (1, 2, 3)