Posted by: tom.guerry (tom.guerry@kp.org) on Tue Nov 27 14:19:04 2007

Jack -

the theory is that the right last quick stretch of the xfactor/muscle tone enables the activation of tissue elastic properties that make the start of unloading more efficient than either muscle reflexes (sretch shortening reflex) or muscular force production (eccentric or concentric) alone.

http://www.advancedmotionmeasurement.com/html/XFactorStretch6.htm

"Research has shown, that extra stretch on muscle, and active resistance to this stretch, can increase the force of contraction of muscle. Several mechanisms are responsible for this. A rapid rotation of the pelvis early in the down swing may trigger sensitive stretch receptors (called muscle spindles) in the muscles to quickly shorten the muscle.
Therefore, as the hips initially rotate forward toward the ball, the maximally stretched rotational muscles of the trunk respond by a faster and more forceful contraction. A second mechanism relates to stored elastic energy in the muscles. The opposing directions of the shoulders and hips at the top of the back swing will stretch the torso muscle facilitating storage and finally release of elastic energy. The end result is that the X-Factor Stretch increases the force production on the down swing, facilitating greater club head speed at impact.
After contrasting the X-Factor at the top of the back swing and at its maximum early in the down swing for highly skilled and less skilled golfers, we found that the X-Factor at the top of the back swing was not significantly larger for the highly skilled players than less skilled players. We also found that both highly skilled and less skilled golfers did increase their X-Factor early in the down swing. They did not immediately begin to rapidly close the X-Factor. Finally, we found that this stretch of the X-Factor early in the down swing was significantly greater for the highly skilled golfers than less skilled golfers."

and

http://www.advancedmotionmeasurement.com/html/XFactorStretch7.htm



"In conclusion our results suggest that:

1- X-Factor Stretch is more important to an effective swing than simply X-Factor at top of back swing and that the X-Factor should actually increase early in the down swing before it rapidly decreases to impact.


2- Also that the aim of the back swing is not just to put the golfer in the correct position for the down swing, but also to dynamically tension the torso muscles correctly to allow them to contract maximally during the down swing, hence generating optimum power."