Although this tactic may be something you are already doing regularly, it is worth mentioning that those who don’t do it are doing themselves a great disservice.
Grunting during a shot is the sudden expulsion of air in a turbulent manner during the striking of a shot. For some time it was hypothesized that the masking of the sound of the ball impacting the tennis racquet’s strings by the sound of grunting could affect the reaction time and judgment of where the ball was going to go after impact.
This hypothesis was tested out in 2010 by Scott Sinett and the results were conclusive. Grunting gives players an advantage over their opponents (if they do not grunt) by a significant margin. The judgment of direction and reaction time were both slowed when a white noise was present during a shot in a video clip of a tennis player hitting a ball.
Additionally, this tactic is fantastic because it requires no unsportsmanlike actions and it actually has empirical support for its effectiveness in affecting your opponent’s perception and therefore his mind game.
So the next time you play against your friend, try grunting on every single ball right as you hit and rest easy in the knowledge that you are getting a scientifically-supported advantage (unless you opponent knows the same thing, of course!)