[Mike O]

Jmessner,
This is one item where Homer Kelley would disagree with the Search for the Perfect Swing.

Prestressed would be the result of a Hitting motion- stressing the shaft or bending it away from the target.- as a result of the "radial acceleration" or pushing against the clubshaft. If you were looking face on to a golfer hitting a golf ball - the clubhead would be back of the hands.

The above concept is important when combined with his formula for ball speed as determined by what happens during impact- I.E. it's the ball speed at separation- not impact that is important- assuming the ball rides on the clubface/head for some period of time.

In contrast, while the swinger has some other advantages that the hitter does not have, the swinger wouldn't have the advantage of a "prestressed" clubshaft - because the nature of the physics is different- the "pulling" on the shaft in this context creates a "bowing up" of the shaft- not a "bowing forward" of the shaft that happens when one is pushing/hitting.