Originally Posted by rkelley
Rotating his forearm about the axis along his forearm (aka pronation or supination) by its very definition, would require any body perpendicular to that axis, namely his racquet in the picture, to change orientation. If Fed pronates his forearm in the picture, the racquet's tip (the axis from the handle to the tip) will go from pointing to the side to pointing at the camera and slightly down. I may not be communicating my meaning well, but it's not something you can disagree with.
I agree that this motion would not change the angle that the racquet makes with the forearm. Flexing or extending his wrist, or radial or ulnar deviation would do that, but not pronation or supination.
Since his arm is almost straight rotating his upper arm at the shoulder about the axis along his upper arm (aka ISR), would have a similar effect on the racquet's orientation as pronation/supination.
Whatever you want to call it, I personally try to get my racquet and arm in the position that Fed has in the picture.
I think you might be having a hard time getting a feel for where his racket is in relation to his forearm from this camera angle. Check out the side view.
Pronation isn't going to make his racket tip point at the camera. All it's doing is closing his racketface towards the ground.