Originally Posted by albesca
Absolutely agree, the arm do nothing without the loading from the legs and core.
But i still on my idea the trunk doesn't have volountary to drag. It musn't rotate as fast as possible.. legs haven't to work in that way during the forward swing.
The shoulder joint have to move at exactly speed needed by the arm... not less... but not more... because the dragging doesn't add power, but by me, destroy the arm coordination.
Ahhh! That's another issue. Your original premise was that UBR played no role in racquet speed. If you rotate as fast as possible, the connection between upper body rotation and arm swing becomes disconnected, because the UBR has completed before the arm swing has begun, and any benefit is lost. There is, however, an optimum speed at which the contribution of UBR to arm swing is maximized. I don't know how to calculate that value, which would be of no practical benefit anyway. But, I know it when I feel it, which is much more useful and practical.