There seems to be the common opinion that core rotation "catapults" the arm forward on the swing, specifically the forehand. When I watch slow motion video, this just doesn't seem to be the case. Instead, it looks like the rotation and the swing happen simultaneously. http://www.youtube.com/watch?v=tZNfUTnBjAk This video shows clearly that dimitrov's uncoiling in the core does not precede the forward swing. The rotation and swing begin at the same time.