Researchers say the loud grunts uttered by tennis pros such as Maria Sharapova appear to slow down their opponents reactions. (Marcio Jose Sanchez/Assoicated Press)

New research suggests the clearly audible grunts unleashed by tennis professionals may be having more of an impact on the game than just cranking up the decibel level on the court.

A study co-authored by University of British Columbia and University of Hawaii researchers suggests grunts may provide players with a leg up on their competition.

Assistant psychology professor Scott Sinnett at the University of Hawaii at Manoa and UBC psychology professor Alan Kingstone looked at the effects of noise on shot perception during a tennis match.

Sinnett was a post-doctoral fellow at UBC who worked alongside Kingstone. Their study findings were published Friday in an online issue of Public Library of Science ONE.

'They were actually slower to respond to the direction of where the ball was going.'—researcher Scott Sinnett

Sinnett said motivation for the research stemmed in part from those who have complained about grunting. They include former world No. 1 player Martina Navratilova who said in a piece in The Times Online that grunting was "cheating."

The researchers enlisted 33 UBC undergrads, none of whom had more than recreational tennis experience and who reported normal hearing and normal or corrected-to-normal vision.

The participants sat about 60 centimetres from a computer screen in a dimly lit and sound-attenuated testing room to look at videos Sinnett had shot of his friend, a former semi-professional tennis player, hitting a ball to either side of a tennis court.

Grunts may misdirect opponents

A total of 384 video clips were made of the player hitting either a forehand or backhand to the left or right of a video camera set up on the baseline of the court opposite the player.

Half of the clips were accompanied with a brief 60-decibel sound overlapping when contact was made with the ball, volume equivalent to a conversation at a three-foot distance. But rather than using actual grunts, researchers created what Sinnett describes as "white noise" comparable to a "shushing sound."

Participants were required to indicate the direction of the shot in each video clip on a keyboard as quickly and accurately as possible. They were to punch the "M" key with their right hand if they thought the shot was going to the right, and the "X" key with their left hand if they though the shot would go left.

"When a participant actually saw a video clip that did contain the grunt, they were actually slower to respond to the direction of where the ball was going and less accurate to respond to where the ball was going," Sinnett said in a phone interview Friday from Honolulu.

"In real life, you could kind of equate that to somebody reacting to the ball that's being hit a little bit later and possibly being wrong-footed more often, which would mean that they actually think the ball might be going to the left, whereas, in effect, the ball is actually going to the right."

Grunts hit 100 decibels

Former Wimbledon singles champ Maria Sharapova has been known to belt out grunts topping 100 decibels.

Sinnett said the fact that the sound level used in the experiment was quieter than real grunts and effects are still seen is "kind of telling in itself."

"If we had a much louder sound, it might actually lead to more profound effects," he said.

Sinnett said the next step in the research would be to see whether expert players are similarly affected — if at all — by grunts.

"Perhaps they have developed some sort of strategy they're not even aware of that kind of diminishes the effect of the extraneous grunt coming from their opponent."

Sinnett noted that grunts are distracting for an opponent. There is a rarely enforced rule in tennis about creating a hindrance for your opponent, which includes grunting. But it's subjective because it's the chair umpire who determines what is considered too loud, he said.

"Perhaps down the road if it does turn out that even in professional tennis that grunting does have an effect, they might have to, I'm not sure, incorporate some sort of sound measure there to see if they're grunting too loud, too often, whatever it might be," he said.