Originally Posted by SystemicAnomaly
... But I do agree that the role of the body -- legs, hip rotation, torso rotation -- is important.
Can you provide any serious proof?
I think that 15% contribution to the racquet speed is not very important for the reason that we have to waste a lot of energy to create fast rotation of 130 - 200 pounds body. IMO it is better first to concentrate on arm actions and then on the body. The arm is much more important. In tennis everything is important, however with varying degrees of importance.