Breathe Man, Breathe!
 
Breathing both BETWEEN points and DURING the point is a very important, and often neglected, aspect of the game!  Players who have learned to properly exhale at contact improve their timing, power, mental focus, and endurance.
 
So how do you test it?
 
Just warmup forehand to forehand.  Is it natural for you to exhale with each hit?  If it feels unnatural, you probably haven’t been doing it!  Now play some points, ask a spectator to stand close and listen for the exhale and watch your chest.