Now that Mexico has won its first game against Cameroon in the World Cup, some might wonder whether Mexico's coach Miguel Herrera is really onto something. You remember Herrera's declaration that his players abstain from sex during the nearly month-long series of games. Is the Mexican team's victory a win for abstinence?



Probably not.

“Probably,” because the question of sex the day before a sports competition has never really been studied in a way that allows for a definitive answer and there likely isn’t an across-the-board answer, suggests Dr. Ian Shrier, past president of the Canadian Academy of Sport and Exercise Medicine.

“We expect sex the night before to be good for some athletes and bad for others,” Shrier told NBC News, “and even good for some athletes at certain times and bad for the same athlete at other times.”

Having sex, at least the way most people have sex most of the time, doesn’t take much energy — about 25 to 50 calories, or about the same amount of work as walking up two flights of stairs. So, assuming World Cup players aren’t cruising bars until 3 a.m., they aren’t going to wear themselves out.

To that point, the Brazilian team — whose coach Luis Felipe Scolari is OK with sex as long as they don't try any bedroom "acrobatics" — also won their World Cup opener. We can't know what the players did before their first game, but Brazil's now retired Ronaldo has been quoted saying that sex before a game "helps you concentrate."

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In fact, the few studies that have tried to look at human physical performance after sex show no difference between abstaining and indulging. A 1968 study in the Journal of Sex Research found men could squeeze a dynamometer, a device that measures force, with their hands just as hard, for just as long the day after having sex as they could when they abstained.

A 2000 study in the Journal of Sports Medicine and Physical Fitness put male athletes on cycle ergometers and found that “sexual activity had no detrimental influence on the maximal workload achieved and on the athletes’ mental concentration.”

The myth that males would be “depleted” by sex dates back at least to the ancient Greeks who thought semen was a source of male power and vitality.



But as Shrier suggests, sex also has psychological effects. “An essential component of performance is clearly how anxious, tense, or nervous the athlete is,” he said, and tests of physical capacity in lab settings don’t address the question of how well the total athlete might perform in a game.



Some athletes might relieve pre-game anxiety and get a better night’s sleep if they had sex, but some might not. And, Shrier explained, “most of the proponents for abstaining from sex give psychological reasons such as decreasing aggression.”

This aspect has never been tested and there may be no way to test it because, as Shrier pointed out, individuals may react in different ways. Sex might help some perform better, cause others to perform worse, and so a study might not show no effect at all.

So anecdote and myth persist.

As a popular boxing website put it, “having sex takes away your motivation to succeed, it weakens your competitive spirit.”

And as Shrier pointed out in a 2000 opinion article in the Clinical Journal of Sport Medicine, runner Marty Liquori said “sex makes you happy, and happy people don’t run a 3:47 mile.”

On the other hand, Buffalo Bills coach Marv Levy demanded his players be separated from their wives before the four consecutive Super Bowls the Bills played. They lost all four.



We'll have to wait to see if Mexico wins the next match on June 17 to test Herrera's theory.

Brian Alexander is a frequent contributor to NBC News and a co-author of “The Chemistry Between Us: Love, Sex, and the Science of Attraction.”