Jannini has found that sex in fact stimulates the production of testosterone, thus boosting aggression.
"After three months without sex, which is not so uncommon for some athletes, testosterone dramatically drops to levels close to children's levels," he said. "Do you think this may be useful for a boxer?"
Scientists dismiss the idea that sex the night before competition has a tiring effect on the athlete or that it could weaken the athlete's muscles.
Lovemaking, after all, is not a very demanding exercise. In general sexual intercourse between married partners expends only 25 to 50 calories, about the energy it takes to walk up two flights of stairs.
Sexual activity could actually help combat muscle pain or other sports injuries in women, according to Barry Komisaruk, a psychology professor at Rutgers University in Newark, New Jersey.
His studies have found that sexual stimulation in women produces a powerful pain-blocking effect. The effect, he says, can last for up to a day in the case of chronic pain such as muscle pain.
"At least one of the mechanisms by which [sex] blocks pain is that it blocks the release of [a neuropeptide called] substance P, which is a pain transmitter," he said.
Komisaruk has also found that vaginal stimulation has a strong effect on muscle tension in the legs, increasing it in some women and decreasing it in others.
Anxiety and Aggression
Much less is known about the psychological effects of sex on athletic performance.
Some experts say coaches may be favoring the abstinence theory simply because they want to make sure young athletes get enough sleep before a big game.
Psychologists have shown there is an optimal level of alertness and anxiety that is necessary to produce the best possible performance. Too much anxiety or too much aggression may result in poor performance.
"If athletes are too anxious and restless the night before an event, then sex may be a relaxing distraction," Shrier wrote in his study.
"If they are already relaxed or, like some athletes, have little interest in sex the night before a big competition, then a good night's sleep is all they need."
The results will depend on individual preferences and routines, Shrier said, adding that consistency is key.
"In general, an athlete should never try something before an important competition that they have not already tried in lesser competitions or practice," he said.
Jannini, the Italian researcher, says the effects of sex vary among athletes.
"Some personalities need more concentration. In this case sex may be a bad idea," he said.
"For other athletes a bit of extra aggression could be the difference" between winning and losing, Jannini said. "In this case I would suggest a complete and satisfactory sexual intercourse the evening before the game."
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