Originally Posted by TheCheese
Federer/Nadal are not using the same WW that players like Roddick are using. Fed/Nadal are coming up and across the ball, bending at the elbow and pulling inwards towards their body, rather than turning at the elbow and wiping the forearm across like a windshield wiper. There was a great post by Will Hamilton about this, where he talked about how the WW technique he teaches is different than the type used by Fed/Nadal and is more like Roddick/Andreev's technique.
The WW finish can be of two nature, essentially: in both instances, it results from a forearm pronation and a wrist deviation (going from ulnar to radial deviation). In ALL cases, that's what happens. However, there are two possible ways of achieving this movement, one being better than the other. The first, most common, involves a simple concentric contraction of the relevant forearm muscles; the second, more efficient, brings the same forearm muscles through a cycle of eccentric and concentric contraction which, if done quickly enough, results in a much faster forearm pronation and wrist deviation.
That's what the stretch-shortening cycle is: the muscle stretches and contracts back faster like it's a rubber band. Players who present a specific type of hand position during the take back also enjoy this benefit when swinging fast enough and it's the case for Nadal, Federer and Roddick (to my best knowledge).
Just to say that what is REALLY important about the WW forehand is there for all of them.
However, you could produce a WW finish that doesn't help your shot -- think of Hewitt or Gonzalez as examples of that. They look both more like Roddick than Federer or Nadal, but despite a similar outlook, their strokes were different in a key part.