http://youtu.be/Z-88G1EXmRY
As Marcos Silva comments, it is important to feel this in your back. The rule is if you can’t feel a muscle working, that is probably because it isn’t. So although there is a small element of rotation in the body, most of the movement comes from the shoulder blade and arm. Turning the palm up when it is close to the body is an excellent thing to do since it stops the shoulder rolling forwards and helps keep it the the back muscles.