AMG - Clubshaft shallowing

[imperfectgolfer]

Jan 26, 2023 21:44:31 GMT -5 dubiousgolfer said:

Dr Mann

In your previous post you tried to reconcile PC and RN data and said:

"By contrast, in the following video Rob Neal states that the average shoulder turn angle tilt at P4 in pro golfers is 40-42 degrees and that it is 55 degrees at impact."

The 55 degrees is not at impact but seems half way in the follow-through.

DG

Do you have any reason to believe that the shoulder turn angle measurement is different at P7 than it is at P7.5/P8?

Jeff.

[dubiousgolfer]

Jan 26, 2023 23:45:09 GMT -5 imperfectgolfer said:

Jan 26, 2023 21:44:31 GMT -5 dubiousgolfer said:

Dr Mann

In your previous post you tried to reconcile PC and RN data and said:

"By contrast, in the following video Rob Neal states that the average shoulder turn angle tilt at P4 in pro golfers is 40-42 degrees and that it is 55 degrees at impact."

The 55 degrees is not at impact but seems half way in the follow-through.

DG

Do you have any reason to believe that the shoulder turn angle measurement is different at P7 than it is at P7.5/P8?

Jeff.

Unless I'm mistaken, it's on the table and graph below. 'Chest Side Bend Max F-Thru' is 52T which is close to the 55 degrees mentioned in the RN video.

The graph also shows progressive increase in trail side bend through P7 , so am assuming that would increase shoulder turn angle tilt too.




Here is another video where PC mentions this from 17:17 -20:40





DG

[imperfectgolfer]

DG,

Good detective work - as usual!

Jeff.

[imperfectgolfer]

In this post I am going to analyse in more depth some of the recent opinions expressed by Milo Lines on the topic of clubshaft shallowing and right lateral bend.

Here again is the recent Milo Lines video on clubshaft shallowing.





He analyses Dustin Johnson's early downswing action between the 3:28 - 4:16 minute time point of his video.

Here are the relevant capture images from his video.

Milo claims that DJ is increasingly adducting his lead arm between those two images and he also claims that the clubshaft is shallowing without any arm motion.

I cannot see any clubshaft shallowing between those two capture images. I also cannot understand why Milo is talking about increasing lead arm adduction as if he is possibly implying that it can cause clubshaft shallowing. How is that possible?

I don't know how Milo defines clubshaft shallowing, but I will provide my definition.

I think that clubshaft shallowing mainly happens between P4.5 => P5.5 and it requires the following features to be present.

1) The clubshaft must be moving to a more horizontal (shallower) swingplane and the angle between the clubshaft and the hand arc path must be increasing.

2) The lead palm, which is on top of the club handle, must be moving in a more horizontal direction and that requires an increased amount of lead forearm pronation if the LFFW remains intact and the lead wrist does not increasingly bow and thereby angle the clubshaft groundwards. An equally useful marker is the watchface area of the lead lower forearm, which must be moving in a more horizontal direction if the clubshaft is shallowing while the LFFW remains continuously intact on a progressively shallowing swingplane.

3) The trail palm, which is below the club handle, must be moving in a more horizontal direction and that requires trail forearm supination if the degree of right angle bend remains relatively unchanged.

So, let's examine Dustin Johnson's clubshaft shallowing action.

Image 1 is at P4 and image 5 is at P5.

The red splined path represents his hand arc path.

Note that DJ's clubshaft is pointing left-of-the-target at P4. Note the magnitude of the angle between the clubshaft and the hand arc path.

Images 2 and 3 show his transition to the downswing. Note how much his hands have moved down the hand arc path. Note that there is no evidence of clubshaft shallowing - i) the angle between his clubshaft and the hand arc path is not increasing; ii) the watchface area of his lead lower forearm is not shallowing; ii) the back of his bowed lead wrist is not shallowing; and iv) his trail palm is not shallowing.

Note that you can first start to see evidence of clubshaft shallowing in images 4 and 5 - note that the angle between the clubshaft and the hand arc path is starting to increase; ii) note that the watchface area of the lead lower forearm, back of the bowed lead wrist and trail palm are all  becoming slightly more horizontal relative to the ground. I also think that the major biomechanical factor causing the clubshaft shallowing action is the fact that his trail upper arm is lowering and adducting towards the side of his trail shirt seam with the elbow leading the hands in a pitch elbow motion (note how his trail elbow drops below the level of his lead elbow causing a counterclockwise rotation of his entire power package assembly as viewed from DTL) + an increasing degree of trail forearm supination.

The second issue that I want to discuss is the phenomenon of right lateral bend (trail side chest bend).

Milo sent me a short movie last night where he demonstrated that he gets his maximum amount of right lateral bend at P5 and that he then rotates his upper torso to P7 while maintaining the same degree of right lateral bend. 

Here are capture images from the movie (which was photographed outdoors at night).

Image 1 is at a simulated P4 position where he has a finite amount of left lateral bend.

Image 2 is at a simulated P5 position (end of the hip squaring phase) where Milo states that he is maximally compressing the right side of his mid-upper torso and thereby acquiring a finite amount of right lateral bend.

Image 3 - Milo then rotates his torso counterclockwise towards a simulated impact position while maintaining the same degree of right lateral bend.

I have a major problem with Milo's demonstration in the sense that it does not reflect the true "real life" reality of what happens in his, and a pro golfer's, downswing.

Most importantly, note that Milo has very little torso-pelvic separation in images 2 and 3 and it is very difficult to obtain a large degree of right lateral bend if there is not a large degree of torso-pelvic separation (and especially much more difficult if the upper torso is slightly more rotated counterclockwise than the pelvis as in image 3).

So, let's consider what actually happens in Dustin Johnson's and Milo's "real life" driver swings.

Capture images of Dustin Johnson's early downswing.

Image 1 is P4, image 2 is at P5, and image 3 is at P5.5.

Note that DJ is maximally "crunching-in" the right side of his mid-upper torso at P5 but he doesn't really have any right lateral bend of his thoracic spine. There is a small degree of right lateral bend manifesting by P5.5, but it is not large in magnitude. I believe that the reason DJ cannot enact a large degree of right lateral bend is because there is not enough torso-pelvic separation where the pelvis leads the upper torso to a significant degree with respect to the degree of counterclockwise rotation.

Now, look at these capture images of Dustin Johnson at impact and P8.

Image 1 is at P4, image 2 is at P5, image 3 is at P7 and image 4 is at P8.

Note that DJ has minimal right lateral bend at P5 despite "crunching-in" the right side of his mid-upper torso.

Note that DJ has a lot of right lateral bend at P7 and even more at P8 and that allows his shoulder turn angle to become progressively steeper (Phil Cheetham's Sportsbox data shows that the average pro golfer has 36 degrees of right chest side-bend at P7 and 52 degrees at P8).

What makes it possible to acquire a much larger degree of right lateral bend between P6 => P8?

I believe that it is due to the large degree of torso-pelvic separation where the pelvis is much more rotated counterclockwise than the upper thoracic area (T1 - T4 vertebra) of the upper torso. That allows a golfer to side-bend much more in a side-rightwards direction. Note how much DJ's pelvis is ahead of his head and upper thoracic torso (from a counterclockwise rotary perspective) in images 3 and 4 and that allows DJs mid-upper torso  to bend much more sideways.

The same phenomenon can be seen in Milo Lines' driver swing action.

Capture images of Milo's early-mid downswing.

Image 1 is at P4, image 2 is at P5, image 3 is at P5.2 and image 4 is at P5.5.

Note that Milo has minimal right lateral bend at P5 despite maximally "crunching-in" the right side of his mid-upper torso.

Note that Milo has more right lateral bend at P5.5, but not much more because it is biomechanically difficult to get a large degree of right lateral bend if the pelvis is only rotated counterclockwise slightly more than the upper torso.

Now, consider what happens in Milo's later downswing and early followthrough.

Note that Milo has a huge amount of right lateral bend at impact (image 3) and even more at P7.8 (image 5).

What makes it biomechanically possible is the fact that his pelvis has rotated much more counterclockwise than his upper torso and that allows him to right side-bend much more. However, a more important factor than the degree of torso-pelvic separation (which is actually less at P7 than it was at P5) is the fact that his head and upper thoracic spine are far back relative to the belt buckle area of the front of his pelvis. I think that it is much easier to get a larger amount of right lateral bend when the entire spine is tilted far back due to a large degree of secondary axis tilt than it is at P5 when the upper swing center is near-vertically aligned over the lower swing center - for the same finite amount of right lateral bending force.

I am very fond of Milo, but I think that his recently expressed opinions are off-track.

I think that Milo's opinions on clubshaft shallowing were very much more on-track in his previous video on the topic of clubshaft shallowing.

In this video, Milo mainly focused on right arm motion, and especially the right forearm's supination phenomenon (which he calls the "door knob opening" move).

Milo states in the video that a beginner golfer may have to manually train himself how to perform the "right arm motion move" pattern in order to get it ingrained into his swing action. I agree with Milo that this "right arm motion" pattern is the key to performing a clubshaft shallowing action.

Milo likens the clubshaft shallowing action to performing a side-arm (stone-skipping) right arm throw action as demonstrated in the following capture images.

In image 1, Milo is standing in a simulated P4 position with a golf ball in his right hand. Note that his right palm is near-vertical.

Note how Milo progressively shallows his right palm in images 2 and 3. What is he doing biomechanically to perform that excellent right palm shallowing action?

From a pivot motion perspective, he is rotating his torso counterclockwise with his pelvis leading his upper torso and that allows him to get his right shoulder lower.

More importantly, note what he is doing with respect to his right arm action. He is lowering and adducting his right upper arm while keeping his right elbow bend angle unchanged and he is also ensuring that his right elbow leads his right hand. Note that he is also markedly supinating his right forearm.

I think that Milo was very on-track in this video and I can fully concur with his golf instructional advice on how best to perform a clubshaft shallowing action by primarily mimicking the right arm motions seen in a "stone-skipping" right arm throw motion.

Jeff.

[playing18]

Thanks DG for the Sportsbox video presentation. It is excellent.

PC makes it clear that L side-bend increases during the backswing and it appears correlated with the lowering of the body after p3, whereas T side-bend increases during the downswing and appears correlated with the elevation or raising of the body. But I imagine that the dynamic rotational ROM of the pelvis in the downswing also influences the T side-bend data as compared to the more tame pelvic motion during the backswing. In any event, the 3D data are essential to understanding spinal side-bend. 

Is there any question that both the backswing and downswing side-bend data are accurate? Is there any question that 3D data is the only reliable way to confirm or correct one's 2D observations? 

The Sportsbox approach to use AI to generate 3D approximated data from 2D capture is genius. It is obviously the way of the future.

Jim - playing18

[imperfectgolfer]

DG,

A question regarding this image

Take the chest bend measurement of 36 degrees at P4.

Is it measured relative to the horizon or relative to the lumbar spine? If it is measured relative to the ground, then that measurement is hugely affected by the degree of hip joint flexion, which is the major factor causally responsible for determining the spinal bend inclination angle.

If the spinal bend inclination angle of the lumbar spine is 36 degrees and the chest bend measurement is also 36 degrees, can one conclude that there is no left lateral bend of the thoracic spine (relative to the lumbar spine)?

Look at this capture image of Collin Morikawa from the Rob Neal video.

Note that I have drawn a line over his P4 image using Photoshop's measurement tool. That line represents his spinal bend inclination angle and it measures 48 degrees. I strongly suspect that the drawn spinal bend inclination angle roughly reflects his lumbar spine angle as it is perceived to be in the sagittal plane. If correct, then it means that there can be very little left-lateral bend of the thoracic spine relative to the lumbar spine at P4.

By contrast, you can clearly see his lumbar spine angle in his P8 image and it is much more vertical, so that to get a 55 degree shoulder turn angle tilt, he must have a lot of right lateral bend of the thoracic spine relative to the lumbar spine.

Here is an upline view of Dustin Johnson at his P4 position

Surely, it is reasonable to assert that his lumbar spine angle is very close to his spinal bend inclination angle and that there is very little left-lateral side-bending of his thoracic spine relative to his lumbar spine.

Jeff.

[dubiousgolfer]

Dr Mann

It says on PC's website

"The spine angles are relative angles calculated from the thorax with respect to the pelvis. Note that if you try to calculate the spine angle from the difference between the pelvis and thorax angles you may not get exactly the same answer as seen in the graphs above. That is because in 3D when there are three simultaneous angles present they do not simply add up, specific 3D relative joint calculations must be used."

In PC's doctoral dissertation he mentions how the virtual local frame of reference in the pelvis is created.

"For the pelvis, a superior point on the left and right greater trochanter is digitized. A ruler is placed on the left lateral side of the pelvis to estimate anterior
tilt. It is placed next to the digitized point on the trochanter and aligned to be parallel with a visualized line from the left PSIS to the pubic symphysis (Burch, 2002). A point several inches above the trochanter point on this ruler is then digitized. In a similar manner to the thorax, these three points are used to create an anatomical coordinate system in the pelvis centered midway between the left and right greater trochanters. One axis is between the trochanters and the other is parallel to the anterior tilt angle of the pelvis, the third is perpendicular to both of these. Thorax and pelvis rotation is calculated using the Joint Coordinate System method (Grood & Suntay, 1983)."

"Side bend is measured in degrees with respect to the horizontal with trail being to the right side for a right hander and lead being to the left side for a right hander. The terms trail and lead are considered to be more appropriate than left and right because they remain consistent with both left and right handed golfers."


Reading the above, I am assuming that the 36L measurement at P4 is the difference between the thorax and pelvis bend relative to the horizontal. I'm unsure how the measurements could be affected if the bending of the thorax was made relative to the lumbar spine instead of some local frame of reference located in the centre of the pelvis.

I'm also unsure how secondary spinal tilt is accounted for in these chest side bend measurements? What if the spine just tilted about 10 degrees from the lower lumbar section with respect to the pelvis without any thoracic bend , would that register 10 degrees chest side bend?

Lots of questions but no confirmed answers.

DG


PS.

From this link below , it seems that there can be 20 degrees of side bend just associated in the lumbar region. So as I've mentioned above, if there is no account taken for this type of spinal bend in the lumbar region, then it could skew the 'chest side bend' measurements.

www.physio-pedia.com/Lumbar_Spine_Range_Of_Motion

Table: Average Healthy Ranges of Motion Measured from Anatomic Position: Lumbar spine[2]

Flexion 50 degrees

Extension 15 degrees

Right lateral flexion 20 degrees

Left lateral flexion 20 degrees

Right rotation 5 degrees

Left rotation 5 degrees

[dubiousgolfer]

I forgot to add that if the chest side bend is measured as the relative side bend measurements of the thorax vs pelvis , then an increase in the chest side bend value , might not necessarily mean there has been increased thorax side bend. It could mean that the increase was caused by some change in tilt of the pelvis.

I think Gears has more segment measurements than AMM3D  define segments such as spine, ribcage , pelvis and it can also measure lateral tilt.


www.gearssports.com/articles/gears-golf-body-metrics/#:~:text=It%20uses%20the%20local%20coordinate,pelvis%2C%20then%20it%20is%20Closed.

Looking at the above url link, still unsure how GEARS define the spine segment and also unsure whether AMM3D measures spinal tilt.

Very frustrating trying to find some amalgamated concise clear information about these 3D systems and how they measure things.

DG

PS.
I think Gears uses a 'virtual' spine segment (Phew!). This is how they define it below:

"Spine – a line drawn between the base of the neck and the middle of the pelvis (will always intersect with the Pelvis Body Line)"

Seems a bit crazy to use that line to measure spinal secondary tilt , especially if there is also thoracic bend of the spine. It might mean there is a net 'geometric' tilt of that line but not necessarily anatomically.

[dubiousgolfer]

Jonathan Taylor claims left lateral flexion of the thoracic spine (in the sagittal plane at P4) in his video below for a more centralised type of spine loading motion (I suspect like C).

Would the degree of left lateral flexion at P4 depend on several factors such as primary and secondary tilt , the backswing plane approaching P4 , pelvic tilt?






TPI  and Dr Greg Rose seems to claim the same.





DG

[imperfectgolfer]

Jan 28, 2023 8:37:12 GMT -5 dubiousgolfer said:

Jonathan Taylor claims left lateral flexion of the thoracic spine (in the sagittal plane at P4) in his video below for a more centralised type of spine loading motion (I suspect like C).

Would the degree of left lateral flexion at P4 depend on several factors such as primary and secondary tilt , the backswing plane approaching P4 , pelvic tilt?






TPI  and Dr Greg Rose seems to claim the same.





DG

I do not know what you mean by using the terms primary and secondary axis tilt with respect to the backswing action. I also do not know what you mean by "backswing plane".

I can agree with Greg Rose that the thoracic spine undergoes left-lateral tilt and extension in the backswing action.

I think that adding more left-lateral bend and extension (what I call an arch-extension maneuver) will convert pattern B to pattern C. If one uses slightly less left-lateral bend and extension then one will have a vertical-centralised backswing loading pattern that is intermediate between pattern B and pattern C.

I think that straightening the trail leg and elevating the trail side of the pelvis at the same time as one extends/left-laterally bends the thoracic spine will convert pattern C into pattern D.

You seem to be implying that chest side-bend is measured relative to the pelvis and not the ground. I cannot understand that claim. Could you please clearly define how chest side-bend is measured and how it takes into account the spinal bend inclination angle that is due to hip joint flexion causing changes in the inclination of the lumbar spine relative to the ground?

Jeff.

[imperfectgolfer]

I have been thinking more about the biomechanical factors that cause a lot of right lateral bend between P6 => P8 and not at P5.

At P4 (image 1), DJ has a fair amount of left-lateral bending and extension of the thoracic spine.

By P5 (image 2) that left-lateral bending and extension has disappeared. DJ is now "crunching-in" the right side of his mid-torso but he only has a minimal amount of right side-bend of the thoracic spine despite applying a large amount of right side-bending force. I now suspect that the presence of anterior pelvic tilt, which produces the spinal bend inclination angle seen in the lumbar spine, prevents the thoracic spine from bending rightwards. Another factor that may limit right lateral bend at P5 is the fact that the upper swing center is stacked over the lower swing center and that may limit one's ability to have a lot of right lateral bend at P5.

Then, look at the scenario at P7 (image 3) and P8 (image 4). Note that three phenomena have happened with respect to his pelvis (compared to P5) - i) it has shifted targetwards, ii) it is much more rotated counterclockwise and iii) he has converted to a posterior pelvic tilt scenario. If pelvic events i) and ii) are happening, and he keeps his head stationary and vertically located over the same ground position between P5 => P7 then he will acquire more secondary axis tilt where the upper thoracic spine is much further away from the target than the pelvis. Then, under the influence of a right lateral bending force applied to the thoracic spine which is more secondary axis tilted and where the golfer is in a condition of posterior pelvic tilt, it is biomechanically much easier for the thoracic spine to tilt rightwards.  Note that DJs right lateral bending tilt angle is behind the pelvic axis (between the left and right hip joints) so the pelvis must be more open than the upper torso during the right lateral bending phenomenon. However, the degree of torso-pelvic separation does not have to be greater at P7 than P5 for the phenomenon of right lateral bending to happen (as I previously wrote).

Jeff. 

[dubiousgolfer]

With regards how I think 'Chest Side Bend' angle is calculated (I can't be certain without having more information regarding the workings of AMM 3D ) I have drawn a simplified picture of the Ribcage and Pelvis segments attaching a frame of reference on T4 and the centre of the pelvis. I have then rotated each frame of reference about the 'x' axis (not shown) which you can regard as pointing straight out of the picture from the origin. The degree of rotation of each frame of reference is an independent measure of side bend for thorax and pelvis.

The 'Thorax T4' frame of reference has rotated alpha 'α' degrees while the pelvis frame of reference has rotated beta 'β' degrees .

My interpretation of 'Chest Side Bend' angle is simply the side bend of the thorax relative to the side bend of the pelvis and will equal α - β .

My example is very simplified and in reality during the golf swing, each frame of reference will be moving with 6 degrees of freedom in 3D space so the mathematical calculations of the 'independent' measure of side bend for thorax and pelvis becomes too complicated to show with diagrams.




DG

[dubiousgolfer]

Dr Mann

You said

I do not know what you mean by using the terms primary and secondary axis tilt with respect to the backswing action. I also do not know what you mean by "backswing plane"

Yes, on reflection I don't see any cause and effect with regards my question above? When I first looked at the Greg Rose video I thought more primary tilt (image below) at address with a flatter backswing would mean being replaced with more left lateral flexion by P4, if the golfer wanted to retain those same primary tilt angles during his whole swing.

Matt Kuchar sprung to mind when I thought of a possible connection.





DG

[dubiousgolfer]

Jan 28, 2023 20:15:58 GMT -5 dubiousgolfer said:

With regards how I think 'Chest Side Bend' angle is calculated (I can't be certain without having more information regarding the workings of AMM 3D ) I have drawn a simplified picture of the Ribcage and Pelvis segments attaching a frame of reference on T4 and the centre of the pelvis. I have then rotated each frame of reference about the 'x' axis (not shown) which you can regard as pointing straight out of the picture from the origin. The degree of rotation of each frame of reference is an independent measure of side bend for thorax and pelvis.

The 'Thorax T4' frame of reference has rotated alpha 'α' degrees while the pelvis frame of reference has rotated beta 'β' degrees .

My interpretation of 'Chest Side Bend' angle is simply the side bend of the thorax relative to the side bend of the pelvis and will equal α - β .

My example is very simplified and in reality during the golf swing, each frame of reference will be moving with 6 degrees of freedom in 3D space so the mathematical calculations of the 'independent' measure of side bend for thorax and pelvis becomes too complicated to show with diagrams.




DG

I have been reading Phil Cheethams blog again and I think I will have to revisit this again.


He said the following :


The spine is defined as the relative motion between the pelvis segment and the thorax segment. 

The side bend angle of a segment is the angle between a side-to-side anatomical axis and the horizontal plane. The anatomical reference axes move with the segment during the swing.


So maybe chest side bend is just alpha 'α' and measured from the horizontal plane.

DG

[dubiousgolfer]

Jan 28, 2023 11:16:57 GMT -5 imperfectgolfer said:

I have been thinking more about the biomechanical factors that cause a lot of right lateral bend between P6 => P8 and not at P5.

At P4 (image 1), DJ has a fair amount of left-lateral bending and extension of the thoracic spine.

By P5 (image 2) that left-lateral bending and extension has disappeared. DJ is now "crunching-in" the right side of his mid-torso but he only has a minimal amount of right side-bend of the thoracic spine despite applying a large amount of right side-bending force. I now suspect that the presence of anterior pelvic tilt, which produces the spinal bend inclination angle seen in the lumbar spine, prevents the thoracic spine from bending rightwards. Another factor that may limit right lateral bend at P5 is the fact that the upper swing center is stacked over the lower swing center and that may limit one's ability to have a lot of right lateral bend at P5.

Then, look at the scenario at P7 (image 3) and P8 (image 4). Note that three phenomena have happened with respect to his pelvis (compared to P5) - i) it has shifted targetwards, ii) it is much more rotated counterclockwise and iii) he has converted to a posterior pelvic tilt scenario. If pelvic events i) and ii) are happening, and he keeps his head stationary and vertically located over the same ground position between P5 => P7 then he will acquire more secondary axis tilt where the upper thoracic spine is much further away from the target than the pelvis. Then, under the influence of a right lateral bending force applied to the thoracic spine which is more secondary axis tilted and where the golfer is in a condition of posterior pelvic tilt, it is biomechanically much easier for the thoracic spine to tilt rightwards.  Note that DJs right lateral bending tilt angle is behind the pelvic axis (between the left and right hip joints) so the pelvis must be more open than the upper torso during the right lateral bending phenomenon. However, the degree of torso-pelvic separation does not have to be greater at P7 than P5 for the phenomenon of right lateral bending to happen (as I previously wrote).

Jeff. 

Dr Mann

You said

"I now suspect that the presence of anterior pelvic tilt, which produces the spinal bend inclination angle seen in the lumbar spine, prevents the thoracic spine from bending rightwards."

I cannot understand how anterior pelvic tilt can have any effect on thoracic side bend ( see image below).  Wouldn't any tilting of the pelvis in the coronal and sagittal planes have an affect only in the vicinity of the the lumbar spine like the images below and have little to no effect on the thoracic spine?







DG