Evidence The Wrist Snap On a Serve Is Real

[stotty]

arm rotation and power

Many good players can start a serve from the trophy position and, without bending their knees and using only minimally the lower segments their body, can serve close to full power.

I think this gives great credence to the theory that upper arm rotations are responsible for an awful lot of power...at least the largest chunk of it.

[John Yandell]

Yes BUT those guys hitting 110mph on their knees etc aren't hitting the high levels of spin. When you see people brag about that stuff they are tossing to the right and hitting flat bullets. The whole body is needed not just the upper.