In his Golf Digest article
Jim McLean states that one should maximise one’s dynamic X-factor at the start of the downswing, and he states that tour players have a dynamic X-factor (X-factor stretch) of 17 degrees. Do you think that a golfer should attempt to obtain a X-factor stretch value of 17 degrees if he has already achieved a maximum static X-factor at the end-backswing position? My own opinions are available in this review paper

Jeff.

Very interesting in depth study (as usually on your site…) of Jim McLean article and thank you for sharing.

On a medical point of view, I’m just a vet, but:
To much torque on the spine maybe a problem. In their textbook Joint Structure and Function, Norkin and Levangie state, “It has been suggested that the annulus fibrosis [of the intervertebral disk] may be the most effective structure in the lumbar region for resisting torsion. However, the risk of rupture of the disk fibers is increased when torsion, heavy axial compression, and bending are combined.”(wich is the case in the golf swing). Interesting reading too: Degenerative Lumbar Disc Disease..

On the mecanical point of view Myers study is a pearl. Many strong points :

High Ball Velocity group (HBV): average 33 years of age , 1,8 handicap
Low Ball Velocity group(LBV) : 58 years , handicap 15
A “young pro group” and a “midle age amateur” group

Difference in the ball velocity at impact:
HBV : 75,4 LBV: 55.7 diff= less 26% for LBV

Difference in the torso rotation at the top:
HBV; 104 LBV: 94 diff= less 10% for LBV

Difference in the uper torso rotation velocity rotation at lead arm parrallel:
HBV; 738,3 LBV: 546,1 diff= – 26% for LBV

So 26% of higher early torso velocity = 26% of higher ball velocity? Not so simple…

Difference in the uper torso rotation velocity rotation at IMPACT:
HBV: 520,1 LBV: 498,7 diff= - 4,2 %

Difference in the velocity lead arm parallel vs IMPACT
HBV= -30% LBV: – 8,2 %

From lead arm parallel position to impact, the “pro” group is dramatically reducing the torso speed of rotation (-30%) and the “Am” group is still travelling less or more at the same speed (-9%)
At impact the upper torso rotation velocity is less than 5% between the two groups !!!

So where the hudge différence (26%) in ball velocity is coming from? How can the pro reduce his speed of rotation by 1/3 and still increase the club head speed ?
Answer: DOWN STROKE SEQUENCE, as reported by Homer Kelley. “Power Acccumulators Release sequence is #4,#1,#2,#3. Any accumulator number may overlap or replace its preceding number, but cannot precede it ”. #4 , Pivot (body ) Power supply the initial acceleration of the Downstroke . Then, in sequence, #1 (bent right arm), #2 (cocked left wrist, the velocity accumulator for M. Kelley), #3 (left forearm/shaft angle) will release their stored potentiel for a maximum velocity (after impact).
X factor stretch is the first stage of the rocket. One piece in a sequence, and the good management af all pieces of the sequence is the “secret” to high ball velocity.
Phew! I’am turning 58 in july, my handicap is 14,9 (everything is true, I’m definitely a LBV guy), but I feel like my back is out of danger.

Phil

In the normal golf swing, the structure of the lumbar vertebra prevent the lumbar spine from being subjected to a large torquing stress because the lumbar vertebra are incapable of lateral flexion or rotation. Virtually all the spinal rotation involves the thoracic vertebra and the torquing tress load is spread over 12 vertebra thereby limiting the rotational torque stress on each thoracic intervertebral disc.

I believe that the large muscles of the torso produce their major effect on ball velocity in the early-mid downswing when both the pelvis and shoulders can rotate very fast. As the golfer approaches impact, his mid-upper torso muscles have already shortened so he cannot actively generate fast shoulder rotation speeds in the late downswing. Both groups of golfers (HBV and LBV group) are in a similar situation in the late downswing from this perspective and one wouldn’t expect there to be a significant difference between the two groups. During the late downswing (when the club has passed the delivery position), the club’s angular momentum becomes the dominant force responsible for a high ball velocity as clubhead release occurs naturally/ automatically according to the simple laws of physics. The best explanation for the release phenomenon is this explanation

The amount of angular momentum gained by the club when it reaches the release point depends on the speed of upper/lower torso rotation in the early-mid downswing, That’s why the HBV group could produce greater ball velocity. Their faster hip and shoulder turn speeds translates into a faster clubshaft speed and greater angular momentum by the time the club reaches its release point. From that point onwards, simple physics primarily dictates the clubhead speed at impact.

Jeff.

Jeff
I totally agree with you (who can go against the science?....)
I was just wondering if some “golf secret” may not be dangerous for the body.
Sorry but we don’t have the same medical information:
Lumbar spine
Flexion: 45° Extens.: 35/45° Lateral inflex.: 20° Axial rotat.: 10/15°
Thoracic spine:
Flexion: 30° Extens.: 40° Lateral inflex.: 30° Axial rotat.: 30°
(http://www.chups.jussieu.fr...)
Mecanicalaspect: thank you for the great explanation link. It seems to emphasize “how to delay the release” and is a good scientific support to this excellent article
Paul Hart on power release
When science confirm experience it makes me feel that we are on the good tracks…
Phil

Phil

There are many reasons why there is so much disagreement about golf biomechanics in golf forums, and one of the main reasons is that we cannot even agree on the basics of human anatomy.

In my article, i posted a photo of the lumbar vertebra showing that it’s facet joint shape is such that it only allows for movement in the saggital plane. You are willing to quote a source of information that claims that that the lumbar spine is capable of a significant degree of lateral flexion and rotation.

Interestingly, with a limited axial rotation ability of 40-45 degrees for both the lumbar and thoracic spine (according to your source), it is amazing that an average golfer can rotate his upper torso 90 degrees, and that the average HBV group golfer in that research study could rotate his upper torso 104 degrees..

I believe that the release phenomenon is essentially a passive phenomenon and that a golfer should have passive wrists/hands while Paul Hart implies that a golfer can actively hold the release.until a predetermined point in time. With such a disparity in beliefs, it is difficult to have a rational argument.

Jeff.

Phil

Interestingly, with a limited axial rotation ability of 40-45 degrees for both the lumbar and thoracic spine (according to your source), it is amazing that an average golfer can rotate his upper torso 90 degrees, and that the average HBV group golfer in that research study could rotate his upper torso 104 degrees…

Jeff.

104° is the angle of rotation of shoulders + pelvis, it is not the axial angle of rotation of the spine!

Phil

I wasn’t implying that the 104 degrees is the required amount of axial rotation required in a full golf swing. In that research study, the pelvic rotation was about 44 degrees and the shoulder rotation about 104 degrees in the HBV group golfers. That’s a torso-pelvic separation differential of about 60 degrees, which is roughly a reflection of a need for an axial rotation of about 60 degrees, which is 15-20 degrees more than the theoretical limit of 40-45 degrees proposed by that source.

Jeff.

Jim McLean’ s table (Golf Magazine article as reported in your first post) :
average gap between shoulders rotation and hip turn (= spinal rotation) for 5 long hitters= 38° wich is effectively close to the limit (40/45) but still less .
For 5 short hitters : 24° with more average hip turn.
Phil

Phil

Here is some real scientific literature.

Lumbar axial rotation

Thoracic spine mobility

Jeff.

Jeffmann: thanks for the links to some great stuff:)

Dear Guru,
I have read some of james articles, he has some good infomation.
but I disagree with 17degrees of stretch through impact.
the optimum stretch Is 15 degrees maximum. The mediums for most golfers is between 10 to 15 degrees of stretch. hips at impact perfect ideal is 35 degrees open left and of target and hip tilt (left hip high,right hip low) 10 degrees. Shoulders open 20 degrees left of target and tilt of spine 22 degrees(left shoulder high and right shoulder low)
the critical factor for the stretch is your hip tilt and shoulder tilt,with out this you simply don’t obtain the x factor stretch.
if you have a level hip and shoulder rotation you will not obtain the xfactor stretch
On the back swing at the top (potential energy) is 2 to1 ratio the perfect ideal is 35 dgrees of hip turn and 70 degrees of shoulder turn. A hip tilt of 10 degrees(right hip high left hip low) and a shoulder (spine angle tilt)of 16 degrees (left shoulder lowe right shoulder high) once again correct tilt is critical to obtain correct x-factor stretch. A level hip turn and shoulder you won’t obtain or feel the x-factor.
This is proven by T.P.I whom provide the biomechanic the perfect ideals and measurements.
One thing which will light up your world impact fix is 100% correct in a static position. When I measured golf machine impact fix with students and measured them using biomechanics their hip tilt was 10 degrees and hips were 35 degrees left of target, shoulders 22 degrees of tilt(spine angle) shoulders open left 20 degrees. PERFECT.
I teach golf machine using a biomechanic vest and so far everything homer kelly has said is 100% correct and measures correct. His science is near on perfect.

One thing you can have all the x-factor you like but with out educated hands you will quit or steer everytime. And anyone would like to challenges this I’m very happy to prove this backed with science. The Golf Machine is the bible of golf.
HOMER KELLY I take my hat off to you, your a genius. Thankyou .
All you guys out there listen to the Dart and guru ,If you all take on board what they say and put it to practice you all would be scratch markers.
Dart and guru the golfing world is privlaged to have guys like you with great knowledge and sharing this knowledge with us.
Thankyou.

Dear Guru,
The Golf Machine is the bible of golf.
Thankyou.

Amen, biomechanic
It’s my prayer book (6th edition) for 2 years now. No parables. Mr Kelley’ 28 years of work bible is a scientifique dissection of the Geometric Golf. Need some time (and some help) and many lectures to appreciate that everything we have to know is in this book. It’s like esperanto langage: wherever they are coming from TGMers are speaking the same golf langage.
And it is not sectarian. I’m sure that Mr Kelley would have been very proud to welcome good fellows on board:)

BiOmechanic: Welcome to the forum.

I am intrigued at the vest tool you mentioned there (Kvest or an iclub vest at a guess). I think that with some swapping of empirical info with Jeffmann that we can all learn a bucket load about different players and player statures – ie limitations that some have and some do not have.

Can u please drop me a line to golfguruATiseekgolf.com :)

Dear BiO,

Great post. Nice to know there is a model number to look at. I’m curious, are these measurments the same for Hitting and Swinging? Also, are they taken at low point or the beginning of impact?

Thanks in advance.

Good question there Spike:)

Hi Spike, great question.
Hitting or Swinging makes no difference.
To create the X-factor all you need is a 2 to 1 ratio (stretch eg hips 30 ,shoulders 60 degrees)on the back swing ,
But you need correct tilt with hips and shoulders .
then you have created what we call potential energy X-factor.

20 degress hips 40 shoulders.
30 hips 60 shoulders (degrees)
40 hips 80 shoulders degrees.
The correct name for the down swing is called K-factor, kinetic energy, (energy in motion).
For example from top of back swing,your hips are at 35degrees and shoulder at 70 PERFECT IDEALS then your x-factor is 35 degrees this is maintained until just before impact as soon as your hands fire your strecth fires and through impact reaches 15 degrees when club head seperation is obtained your K factor becomes zero you have released all your energy at impact.
you even use this for punch shots.
to create x-factor ideals should be for hips between 30 to 40 degrees, shoulders are between 60 to 80 degrees. hitting or swinging.
this is for the correct effiency of a golf swing.
Hips fire first,shoulders then arms. educated hands create this effect even though we feel we are firing our arms first it’s an illusion.But the sequence above is only caused by educated hands.
This is using K-vest which captures 120 frames per second.
your hips move at 300 frames per second,shoulders 600 and arms at 1200 frames per second

ooooh my head hurts, what a read.

You write that the X-factor value of 35 degrees is maintained all the way through the downswing until just before impact. I believe that scientific evidence from research studies proves you wrong.

Look at this research study’s results.

Table

One can readily see that the shoulders are rotating faster than the hips in the early-mid downswing and that the degree of torso-pelvic separation is therefore decreasing in the early-mid downswing, and not staying constant.

Here is a photo example.

X factor value

One can see that the degree of torso-pelvic separation is decreasing in the early downswing – from 48 degrees to 37 degrees by the end of the early downswing (when the lead arm is parallel to the ground).

Jeff.

OK so that is the start down acceleration. How about reloading the body for an extra thrust through the ball to maintain rhythm.

If the shoulders overtake the hips gradually we call that using a short radius, a shoulder radius for normal power.

If that overtaking rate is condensed nearer the ball we call that an ankle radius and has a more massive impact.

Once again it is up to the player and BIO is not wrong.

Wrong is not a useful word in golf and life. Better or worse depending on the situation and for what purpose.

Even if we took statistics on the same golfer hitting with a full radius or half radius the results might not be conclusive because he could be holding the connection to his feet with out stretching the muscles.

There is a bit more to this than collecting data. There is understanding what is going on and what is possible.

Ist. Year Kinesiology; The faster a muscle is stretched and the slower it is contracted the more power it develops.

I suppose that applies to abdominal obliques as well.

Dart you are correct and I agree with what your saying,
But when you measure this dart with out you knowing you are gaining a stretch at some point.
I didn’t believe this myself until I measuerd this. Hard to believe dart I know I questioned this myself but proven.
there is a range between 10 to 15 degrees a short radius measures in at ten which is perfect.
Interesting note is impact always measures with in the ranges,
includung degrees of hip turn amount of tilt(left hip high right hip lowe) shoulder turn. Shouler tilt(left shoulder high left shoulder lowe).
One thing I love about measuring using biomechanics more golf machine proves all their therieos correct.
After you told me to drive with ankle I measured this and I still had stretch.Fascinating stuff

Satisfying!

Paul H

I don’t think that the shoulders ever overtake the hips in the downswing. They move faster than the hips in the early-mid downswing, so that the degree of torso-pelvic separation decreases in the early-mid downswing. At impact, the pelvis is open about 40 degrees and shoulders 20 degrees (on average).

I have no idea what you are talking about when you state that “the body must be reloaded for extra thrust to maintain rhythm.”

Biomechanic

You talk of a stretch of 10 degrees. What are you talking about? Do you have a source of reference material that I can read to understand what you believe regarding golf biomechanics?

Jeff.

T.P.I
they are the guys whom come up with these measurements.
T.P.I measurements are now used in all biomechanic technology.
Also bentley kinetics whom are the leaders in america and have been researching these figure for sixteen years before releasing their facts and figures into the golfing world.
Jeffman i can back dart he is right the hips decelerate just before impact the shoulders catch up and over take the hips after impact.
just before impact the stretch is between 15 to 35, the perfect ideal is 35 for good player before impact, but when the hands fire the stretch through impact becomes between 10 to 15 degrees.
hips are between 30 to 35 is optimum range. 40 degrees is boarder line. although when maesures stretch at impact the seperation is still between 15 to 10 degrees. I’m yet to see anymore and I teach biomechanics everyday and yet to see this.
Jeffman in all honesty i’m not concerned what Tiger measures at the end of the day who can swing it like tiger woods or ben hogan.
I relating to the average golfer with normal flexiablities not legends.
I think this is where we all go wrong instead of worrying about how woods and hogan swing lets worry about how we swing and work out what works for us. And swing the club suited to our bodies capabilities.
First thing I do when I give a lesson is work out how much flexability my students have and what their ability is and work form there. If we all went off ben hogan and tiger woods measuresments none of us could play golf.

Biomechanic

None of my ideas only apply to TW and BH. They apply to all golfers.

Have you ever read the book’ “Swing Like a Pro” where the authors base their swing model (ModelPro) on the swings of 100s of professional golfers?

This what they demonstrate regarding shoulders catching up to the hips in the downswing.

Early-mid downswing

Impact – the hip-shoulder alignments

What is “stretch”” Can you precisely define how the “stretch” measurements are made, and the biomechanical foundation for any belief regarding “correct” stretch values at different points in the downwsing?

What do you mean by the term “hands firing”? When do the hands fire, and what is the force causing the hands to fire?

Jeff.

What do you mean by the term “hands firing”? When do the hands fire, and what is the force causing the hands to fire?

Jeff.

Now that is a great question! A trip to one of the Road Shows with The Dart and The Guru might clear up a lot in that area. :)