Originally Posted by rkelley
Well, I would advise the opposite of what you're saying here. The legs, trunk, and shoulders provide the power. They start the swing. The arms and the racquet whip around and the head of the racquet whips into the ball. The arms and wrist do some fine tuning as to exactly when the whip is cracked and exactly where the racquet head goes - that's why you keep your eye on the ball through impact - but the legs, trunk, and shoulders start the swing and provide the power.
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.