Since inverting the racquet (with an eastern grip) allows you to pronate and coil your forearm, are you saying it enables you to swing faster to generate more spin?
So, basically, there's two issues:
As you know, the topspin issue really is about hand rotation. The larger the arc, the more the hand rotates through the hitting zone. Thus the more topspin you can generate without altering the swing plane of the hitting arm.
There's various variables that influences the size the arc. The degree you coil/pronate the forearm in the unit turn is one of them. Depending on grip, most WWers pronate forearm about 45-90 degrees, so that the racquet is first established on edge. Because Federer is inverting his racquet
with an Eastern grip, he's getting close to 180 degrees. This is of the techniques he uses to increase the effective arc of his hand rotation.
Typically, the forearm supinates and pronates (i.e. the supination-pronation cycle) through the stroke of a swing. At the transition point between backswing and forward swing, the forearm has to supinate in order to open up racquet face properly. And then, the forearm naturally pronates through the forward stroke as you finish the stroke. That pronation facilitates hand rotation.
The more your forearm has to supinate, the more it will pronate. By precoiling the forearm during the unit turn, you basically force your forearm to supinate a lot more in order to open up the racquet face. And that in turn means you'll get more pronation through the forward swing and therefore more hand rotation. More topspin.
The second issue, the pace, is influenced by the laid-back position of the wrist. Because the above technique causes the forearm to supinate more to establish hitting position, your wrist will also naturally be much further back in the hitting position. A more laid-back wrist means you now have a "longer" line to accelerate the racquet before it comes around. It's effectively the same as increasing your arm extension in the unit turn to increase the swing arc. BUT, you get this without changing the arm structure of your stroke.
As a result, racquet head speed goes up too. And because you're using an Eastern grip, most of that speed goes into increasing pace on the ball. As a result, you now have a heavier shot.
Federer isn't the only one who does this. Sampras and Scud did something similar, as did Laver. Safin inverts his racquet with a conservative SW .
is Federer just taking his racquet back with the racquet face facing the ground like Sampras, but unlike Sampras maintaining this position while laying back the wrist?
Federer's backswing really deserves its own thread. My hunch is that, through watching videos or learning from his Aussie coach, he ended up modeling his swing after Laver, albeit with modern WW mechanics. There's mechanical things that Laver uniquely did in his stroke, which are also seen in Fed's stroke.
And, in fact, you can argue that the Federer FH is really Laver 2K.
