After four years of anticipation and endless hours of training, soccer players from 32 countries are doing everything they can to play their best at the World Cup. Among their last-minute preparations in South Africa, the athletes are eating well and sleeping enough. They might also be abstaining from sex — or not.

According to news reports, the Argentine team doctor has given the team his permission to have sex with their usual partners during the tournament. Sex is also allowed for Brazilian players.

The players from England, however, will be allowed to see their wives and girlfriends just once after each game, maybe less if they keep winning. Partners of the British players cannot stay overnight. There is no sex allowed, and the coach will be monitoring their behavior through TVs in their hotel rooms.

While the United States team spokesman Neil Buethe declined to comment for this story on guidelines for the American players, experts side with the South Americans. Despite a long history of myth, there is no evidence that sex impairs athletic performance.

"Coaches over the past four, five or six decades have stated that their players should not engage in sex before athletic events because it will weaken their performance without any serious research to support that or any base of scientific theory to understand why that's wrong," said Tommy Boone, an exercise physiologist at the College of St. Scholastica in Duluth, Minn., and author of "Sex Before Athletic Competition: Myth or Fact."

"There simply isn't anything in the medical literature to support abstinence."

Boone led one of only a handful of studies that have actually looked at how sex might alter performance on the playing field.

In a 1995 study, he challenged 11 men to a treadmill test. Some had sex 12 hours before the test. Some abstained. Results, published in the Journal of Sports Medicine and Physical Fitness, showed no difference between the groups in how much oxygen their hearts needed or how efficiently their bodies used oxygen.

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A man's body does go through some physical changes during sex, including a rise in heart rate from 70 beats per minute at rest to up to 130 beats per minute. His blood pressure also goes up. And with more muscle contractions, his body uses more oxygen than it would if he were watching TV.

But compared to the exertion required during a World Cup soccer game, Boone said, sex requires less than 25 percent of the aerobic effort. And it lasts for much less time. There's no way that a quick romp under the covers could sap an athlete's energy enough to make a difference in his game.

In other studies, sex has had no effect on strength, power or endurance, added Ian Shrier, a sports medicine expert at McGill University in Montreal.

"Sex is mild exercise and does not fatigue the body," Shrier said. "Hormonal spikes are controversial. And even if they did occur, it wouldn't matter because they have to affect performance through physical or psychological mechanisms. We know there are no physical effects."

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As far as psychology goes, that's something that has yet to be tested, Shrier said, and the psychological effects of sex might differ from one athlete to the next — by improving focus in some but diminishing it in others. Sex, in other words, is just one of many factors that will determine who will win and who will lose at this year's World Cup.

As for the fans, there is no evidence that sex will impair your tournament-watching experience, but many fanatics appear to be able to live without it. In a recent poll of German soccer fans, 95 percent said they'd rather watch their team play than join their partners in bed.

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