As you rotate your torso through the ball and start to lift the arm, you must keep your hand back. This will let you lift and drive the entire arm, from the shoulder to the hand, through and up the ball. In the Safin and Nalbandian clips, watch how they keep their hand back as they lift the entire hitting arm up and through the ball. This causes their entire right side - hand, shoulder, arm, and racket to come up and through the ball together. That's a lot of BODY MASS driving through the ball.

The final finish indicates how these players have driven the entire right side of their bodies through and over the ball. Note the chin touching the shoulder and the elbow and the buttcap of his racket pointing at the net. This is a perfect indication that they have ripped through the ball with the MASS of the entire right side of their bodies.