Originally Posted by WildVolley
Looking at the video of Djokovic hitting backhands that you've cited:
I believe I see a slight amount of elbow extension into that shot (I'm talking about Djokovic's left arm). Watch it and note whether his left arm straightens from the end of the takeback to hitting the ball. I believe he is marginally extending the elbow (straightening the arm) into the 2hbh. If anything, I believe he hits it with a straighter arm than he does with his fh.
Watching these videos, most 2hbh players have much less of a loop takeback on the bh-side as compared to the fh-side. Especially for players who hit a fh with a fairly straight arm (Nadal, Federer, Verdasco) the arm is bent more in the takeback and therefore there has to be straightening (elbow extension) prior to the shot. My interest in this extension is whether it is also helping some sort of reflex rather than just extending the arm straighter and perhaps allowing a greater arc on the swing and thereby easier pace and spin.
How long is a forward swing for a double handed backhand (in miliseconds)?
In the case of FOREHAND the corresponding number is below 250 miliseconds