Originally Posted by toly
When we rotate trunk with acceleration, IMO the passive arm will never whip around the body. Thus, the arm and its parts should be active, or we should slow down trunk acceleration. Does it make any sense?
If trunk doesn’t rotate at all, the arm by itself still can rotate around shoulder joint etc. I believe that good athlete can hit 100 mph FH without trunk rotation, by using just active arm motions. He will never be able to do that with passive arm relying on whip effect. I tried it many times and always got pathetic FH.
When folks talk about "passive arm" it's not to say the muscles in the chest, arm and wrist are not being used, but the majority of the power is coming from the core rotation that starts with the legs, then through the hips and shoulders. Assuming that the arm is still attached to the shoulder at this point it has to whip around the body.
Check out this video, 0:36. This is what's happening: http://www.youtube.com/watch?v=EMNtq...eature=related
And here's a video that shows the whipping action in the full forehand stroke: http://www.youtube.com/watch?v=EMNtq...eature=related
If you try to hit 100 mph forehands with just your arms, assuming that's even possible, I think you'll tear your shoulder apart pretty quickly.