You can really see the "double rotation" into the ball in this monstrous forehand by Juan Monaco.
First, Monaco uncoils his shoulder/torso towards the net as his
hitting arm locks into a "double bend" position. Notice how
his torso is almost facing the net while the butt cap of
the racket faces the net and his strings face the side fence.
By opening the shoulders/torso first, it creates a stretch
and pull of the entire double bend, which lags behind.
Now Monaco will continue to rotate his
torso into contact, but at the same time, the entire double bend
will rotate into the ball. Notice how his racket is the last
thing to come into the ball, because it is the last link in
the torso/double bend chain. The racket never swings ahead of
or speeds up in front of the larger double bend structure. Instead
the entire double bend structre rotates into the ball along with the torso..
On contact, everything is perfectly lined up and Monaco
can rip the ball with a full wiper motion, using his entire
arm and shoulder to drive the ball.