Predicting the outcome of a tennis match may be as simple as listening to the players' grunts. Specifically, it's the pitch of the grunts that seems to indicate whether a player is going to win a match, according to a study from the University of Sussex.

Psychologists analyzed 50 grunts from the 30 best players in the world—grunts during serves, backhand shots, and forehand shots—and found that the players' grunts were higher-pitched during losing matches. Even more interesting? Those grunts didn't just get higher as the match progressed—they were high-pitched from the very start of the match.

"This suggests that this shift in pitch is not due to short-term changes in scoreboard dominance, but, instead, may reflect longer-term physiological or psychological factors that may manifest even before the match," said Jordan Raine, doctoral researcher and (not coincidentally) tennis captain at the university. Among those factors: previous encounters between competitors, form, world ranking, fatigue, and injuries.

Even weirder: Detecting the difference between winning and losing grunts doesn't even take a scientific analysis, according to the study. When competitive tennis players heard short clips of other players' grunts out of context, they were able to tell which of the players' grunts was from a winning match and which was from a losing match.

And these findings might apply to more than just predicting a tennis match outcome. There are plenty of other athletic situations where you might find yourself grunting, like in the gym. So, if this study's findings apply across the athletic spectrum, pay close attention and you might be able to tell whether today's the day to try and hit that one-rep max.