There’s no evidence to support the idea that sportspeople benefit from abstaining the night before an event, or that having sex impairs performance the next day, say researchers at the University of Florence.
They sifted through hundreds of studies to discover whether there was any truth to the idea—but it seems that sex the night before either has no effect or could even help some athletes. One study found that marathon runners ran better the next day.
Then only real effect might be psychological, especially if the athlete comes from a culture or background where casual sex is frowned upon. But as it’s a truism that sport is as much a mental as a physical pursuit, any guilty thoughts may have a negative impact.