Originally Posted by cluelessmoose
This is also my current thinking on the matter. I think it has to do with the rebound speed of the frame. When stiffness is measured on an RDC machine I believe a set force is applied to the racket the "stiffness" is just a reflection of how far the racket bends when this constant is applied. So, this number would not directly reflect how quickly or efficiently the racket returns to it's natural state after striking a ball.
Rebound speed is irrelevant. There is not a racquet on the market today that rebounds to it's original or "natural state" before the ball has left the strings. A racquet must be significantly stiffer than anything in production to rebound before the ball has taken off.