The Difference between X-Factor and X-Factor Stretch

From articles that I have recently seen in popular golf magazines it has become apparent to me that there is a misunderstanding of the term “X-Factor Stretch” and that it is confused with the basic X-Factor term.  These two terms, in fact, describe two different measurements in the golf swing; which I would now like to explain.  

The term X-Factor was coined by John Andrisani of Golf Magazine and made popular by Jim McLean in his article “Widen the Gap” (McClean, 1992).  The term was used to describe the difference in the turn angle between the shoulders (upper body) and the hips (pelvis).  For example if you turned your shoulders 90 degrees at the top of backswing and your hips were at 50 degrees then your X-Factor would be 40 degrees; i.e. 90 – 50.  X-Factor has also been termed “coil” and we at TPI call it “Spine Rotation”.  In research carried out by Mike McTeigue et. al. (1994) he concluded that long hitters “generated more of the turn” in the backswing from the X-Factor than the rest of the PGA tour professionals in the group that he studied.  So it was concluded that a large X-Factor at the top of backswing was key to hitting the ball far.

In our research (Cheetham et. al., 2001) we looked at another variable in the downswing and I coined the term X-Factor Stretch to describe it.  X-Factor Stretch is the increase in the X-Factor at the beginning of the downswing produced by the hips starting down before the shoulders, it is also called “Downswing Loading” at TPI.  So if at the top of the backswing the shoulders are turned at 90 degrees and the pelvis at 50 degrees then the X-Factor is 40 degrees, as already explained, but now if the pelvis begins the downswing before the upper body, the X-Factor will get larger (i.e. stretch).  For example, if the hips turn in the downswing to 45 degrees before the shoulders change from 90 degrees, then the X-Factor has increased from 40 degrees to 45 degrees.  The X-Factor Stretch is 45 – 40 or 5 degrees.  So the X-Factor Stretch is the amount of increase in the X-Factor due to the hips starting down before the shoulders.

The X-Factor Stretch is a good thing in the golf swing, in our research we found that the X-Factor Stretch was significantly larger in the high skilled golfers than in the less skilled golfers, but the X-Factor wasn’t.  We concluded that the X-Factor Stretch was more important than the X-Factor.  In muscle physiology this is known as the “Strech-Shorten Cycle” and from a biomechanical point of view the X-Factor Stretch does several important things that increase the force in the downswing:

·       increases the force in the core muscles to a level higher than at the top of backswing,

·       elicits the stretch reflex in the core muscles again allowing them to contract stronger,

·       increases the amount of stored elastic energy in the muscles.

All these add up to a faster club head speed at impact. 

So in summary:

X-Factor is the amount of coil at the top of backswing and is the difference between shoulder turn and hip turn, e.g. 90 degrees of shoulder turn and 50 degrees of hip (pelvis) turn equals a 40 degree X-Factor.  TPI Tour average for X-Factor at pelvis transition is about 42 degrees.

X-Factor Stretch is the maximum increase in the X-Factor due to the pelvis starting the downswing before the shoulders.  X-Factor Stretch equals maximum X-Factor during downswing minus X-Factor when hips begin the downswing, e.g. 45 - 40 = 5 degrees of stretch.  TPI Tour average for X-Factor Stretch is about 5 degrees.

References

Cheetham, P.J., Martin, P.E., Mottram, R.E., and St Laurent, B.F. The importance of stretching the "X-Factor" in the downswing of golf: The "X-Factor Stretch." In P.R. Thomas (Ed.), Optimising performance in golf (pp. 192-199). Brisbane, Australia: Australian Academic Press. ISBN 1 875378 37 5. 2001.  Also reprinted by permission in the inaugural issue of Journal of Applied Golf Research (2011).

McLean, J. Widen the gap. Golf Magazine. pp. 49-53. December, 1992.

McTeigue, M., Lamb, S. R., Mottram, R., and Pirozzolo, F. Spine and hip motion analysis during the golf swing. Science and Golf II: Proceedings of the World Scientific Congress of Golf. Edited by A.J. Cochran and M.R. Farrally. E & FN Spon, London. pp. 50-58. 1994.

Phil Cheetham 3/27/2011

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