DIsclaimer: if you don't like technical discussion you don't need to participate so save comments on how little need there is for this thread for the general player section. we all agree that shoulder ISR is very important in FH and serves. However I think that there is a misconception on what ISR does in serves and bent arm FHs. most people think that in serves first the arm straightens and then ISR supports pronation in moving the rackethead around the hand. however I don't think that this is the main effect of ISR in serves. ISR is also found to be a big contributor in throwing were long axis rotation of the arm only plays a minor role. I believe that most of the ISR works before the arm is extended in accelerating the hand forward. with a bent arm ISR doesn't rotate the arm around the long axis but moves the hand forward. http://www.youtube.com/watch?v=x44CmqKFuMQ that is what ISR does in the overhead throw: http://www.youtube.com/watch?v=cJnm9bC2mag I believe that aspect is a very underrated aspect of the bent arm FH. the bent arm FH will de-couple ISR and pronation, i.e first the shoulder will ISR while the forearm is still supinated moving the hand forward and then the forearm will pronate and move the racket around the hand. with a straight arm FH both moves are coupled. I think that is aspect is the explanation why both FHs produce the same ball and racket speeds. people always talk that SA FH is biomechanically superior because of longer levers and more stretch in the whole arm. that is true however you have to consider that the DB FH has another link in the kinetic chain. it cannot use the stretch reflex in the ISR muscles to generate RHS but it will use that stretch reflex to accelerate the hand which then stretches the forearm to accelerate the racket. I have no data but I believe that BD FHs create higher maximum hand velocities but lower relative (to hand) racket velocities. the resultant velocities for both will be quite similar for both styles but only if you use ISR correctly (not externally rotate as the racket lays back but earlier so that the arm already IRs when the forearm starts to supinate) otherwise if you just drag the arm the SA FH will produce more speed. I think that aspect is very underrated when studying SA vs DB FH and explains quite well why in reality both FHs produce the same ball velocities (although I believe that the SA FH might have a slightly better vertical component and thus spin potential while the DB FH might have slightly more horizontal component).