Tennis players, let it all out: A new study finds that a grunt released with a swing may slow an opponent's reaction time.

The findings, published in the Oct. 1 issue of the online journal Public Library of Science ONE, suggest complaints from some tennis pros that grunting opponents throw off their game may be justified.

Grunting tennis players made the news during the 2009 Wimbledon Championships, when tennis officials announced that they were considering fines for serial grunters. Referees can currently award points against players who seem to be deliberately disturbing their opponents, but many players have said that they simply grunt to focus their energy during a swing.

In the current study, 33 undergraduate students watched tennis players hitting balls across the tennis court. Each shot was either quiet or contained a brief "unnh" noise that occurred as the player struck the ball.

The participants were asked to enter the direction of the shot in each clip on a keyboard, answering as quickly and accurately as possible. As it turned out, the extraneous sound significantly slowed the students' response times. They also made more mistakes in entering the direction of the shots with grunts.

The findings need to be validated on the court, but study author Scott Sinnett, a professor of psychology at the University of Hawai'i at Mānoa, said in a statement that real-world consequences involving more complex motor skills (like hitting a tennis ball) are likely to be profound.

"This is the first study to look at the issue of grunting in tennis," Sinnett said. "Our current work is also looking at how advanced and professional tennis players perform, to determine if they have developed any strategies to limit the negative effects of a grunting opponent."