The position for a power shot

"Every shot is a power shot" Sounds familiar? This is the phrase by Maria for her canon advertisement. Look at her posture for her serve and

it is no wonder her shots are power shots. Maria is one of those female players with great serving power and that comes certainly not without any training. Noticed how her elbow is positioned. The elbow is facing upright not to much to the back and not too much to the front. With her elbow at this position, she can have adequate power to do a smack on the ball.
(Getty images)