Rotation Of Left Forearm But No Rotation Of Right Forearm?

[dubiousgolfer]

Dr Mann

I have been looking at Kirk Junge video below but I cannot understand how he can claim a particular right forearm supination/grip at set up that can prevent the right forearm from supinating/pronating on the backswing/downswing (with a neutral left hand grip).

I am assuming he must be pronating his left forearm in the backswing , so doesn't that mean his right forearm has to supinate? 

[imperfectgolfer]

Sept 2, 2018 18:59:33 GMT -5 dubiousgolfer said:

Dr Mann

I have been looking at Kirk Junge video below but I cannot understand how he can claim a particular right forearm supination/grip at set up that can prevent the right forearm from supinating/pronating on the backswing/downswing (with a neutral left hand grip).

I am assuming he must be pronating his left forearm in the backswing , so doesn't that mean his right forearm has to supinate? 

You are correct!

Kirke Junge is totally wrong to claim that the right forearm is not rotating in a pronatory direction in his demonstrated downswing. Look at him between the 2:00 minute and 2:01 minute time point of the video - note that his right forearm is supinating in his backswing action when he bends his right elbow, and that his right forearm is moving from being supinated to a more neutral position by simulated impact (as he straightens his right arm).

Then stop the video at the 2:10 minute time point when he is at the P3 position. Note that his clubshaft is parallel to the inclined plane (where the plane is just below the TSP), and his right palm is under the clubshaft and his right palm is parallel to the inclined plane, and that right palm alignment requires his right forearm to be supinated more than it was at address.

I also added a comment to the Kirk Junge video's comment section.

Jeff.

[dubiousgolfer]

Many thanks Dr Mann - looks like Kirk has replied to you.

I was wondering if there are 'opposing' secondary actions being caused on the right forearm by:

1. The pronation of the left forearm which will cause right forearm to 'supinate'.
2. The radial deviation of the left wrist (creating PA2) which may cause right wrist circumduction (dorsi-flex and then radial deviate -causing a 'pronation' of the right forearm).

Couldn't the combination of the above negate a net right forearm rotation?

Point number 2 seems to occur (individually for me) and something I found out myself when I produced this video below sometime ago.

www.youtube.com/watch?v=Yht4hgDYYac

DG

[imperfectgolfer]

Sept 3, 2018 5:29:33 GMT -5 dubiousgolfer said:

Many thanks Dr Mann - looks like Kirk has replied to you.

I was wondering if there are 'opposing' secondary actions being caused on the right forearm by:

1. The pronation of the left forearm which will cause right forearm to 'supinate'.
2. The radial deviation of the left wrist (creating PA2) which may cause right wrist circumduction (dorsi-flex and then radial deviate -causing a 'pronation' of the right forearm).

Couldn't the combination of the above negate a net right forearm rotation?

Point number 2 seems to occur (individually for me) and something I found out myself when I produced this video below sometime ago.

www.youtube.com/watch?v=Yht4hgDYYac

DG


DB,

I read Kirk's reply to my comment.

Here is my latest rebuttal comment (in italics).

Kirk,

Look at your video between the 1:47 minute and the 2:04 minute time point - You are supinating your right forearm at address, but it still has to supinate more as you bend your right elbow, and it then rotates in the opposite (pronatory) direction when you straighten your right elbow during your simulated downswing action. Pre-supinating the right forearm at address only decreases the amount of clockwise rotation of the right forearm happening in the backswing, and it doesn't eliminate the need to pronate the right forearm during the late downswing.

Here are capture images from your video.

perfectgolfswingreview.net/JungeRightForearm.jpg

In image 1, your right antecubital fossa is facing the camera and your right radial bone just above your right wrist crease is maximally supinated so that your right palm faces skywards and it is parallel to the ground. That allows your clubface to become parallel to the ground.

In image 2, your right radial bone just above your right wrist is only partially supinated relative to your right antecubital fossa. Note that your right palm is not parallel to the ground, but angled relative to the ground. Note that your clubface is vertical.

Note that your clubface has rotated 90 degrees between image 1 and image 2 and I think that you are totally wrong to believe that it is biomechanically possible to go from a horizontal clubface in image 1 to a vertical clubface in image 2 without pronating your right forearm. Look at your video between the 2:00 - 2:02 minute time point when you hold the club with only your right hand - note how much your right forearm is pronating as you move your right arm from a bent alignment to a straight alignment and when you move the clubface from being horizontal to the ground to being vertical to the ground. What do you think is causing your clubface to rotate 90 degrees during that demonstration if it is not due to right forearm pronation?

Right wrist bending during the backswing action can cause a certain amount of clockwise rotation of the clubface via the phenomenon of right wrist circumduction, but that can only happen if the right wrist does not remain level. However, during a RFT action, a golfer should try and keep the right wrist relatively level between P1 and P2.5, and significant right wrist radial deviation only happens in the later backswing action. Note that right wrist circumduction does not happen in Kirk's video demonstration using the right arm alone (between the 2:00-2:02 minute time point of his video) because he moves the clubshaft in line with his right forearm.

Jeff.

[imperfectgolfer]

Here is Kirk Junge's latest counterargument-:

"It is easy to see that the right elbow bend, and right wrist are allowing the club to open, and close without forearm rotation. All you need to do is pickup a club and copy what you see me doing. I actually can see that there is no rotation either way in the arm when done properly. I do not think anybody expects ZERO rotation as we are all human beings, but I would bet that it is very close to ZERO and if one could practice on 3D equipement this could be perfected.

The club also opens a great deal relative to the target line because of the body rotation. You also have lead arm rotation and then the right wrist and elbow. Easy to emulate if you try.

Your pictures cannot present an accurate image of what is happening due to the angle shot from. The camera would need to be perpendicular to the plane to see it. That is why there are 3D systems out there."

Here is my latest rebuttal-: "I do not believe that "right elbow bending and the right wrist are allowing the clubface to open" as you incorrectly believe. How is that possible?

In your demonstration, the clubface is rotating 90 degrees to being parallel to the ground in image 1 and then becoming vertical to the ground in image 2. How can right elbow flexion/extension change the clubface angle by 90 degrees - if there is no rotation happening at the level of the right elbow joint during a flexion => extension action? How can any motion at the level of the right wrist cause the clubface to open in your simulated backswing action, and then close in your simulated downswing action - if your right wrist remains level and if there is no right wrist circumduction happening?

How can body rotation INDEPENDENTLY cause any rotation of the clubface during a golf swing action? It is not possible!!! It is simple to prove - hold your right forearm parallel to the ground and maximally supinate your right forearm so that your right palm and clubface are parallel to the ground. Then, rotate your body as much as possible WHILE MAINTAINING YOUR RIGHT FOREARM'S SUPINATORY ALIGNMENT UNCHANGED and you will note that you clubface does not rotate 90 degrees from being parallel to the ground to becoming vertical to the ground. In fact, the clubface does not rotate at all!

Finally, you wrote-: "All you need to do is pickup a club and copy what you see me doing. I actually can see that there is no rotation either way in the arm when done properly." That comment demonstrates your ignorance regarding human biomechanics - because one would not expect the humerus or upper forearm to rotate during your demonstration when the clubface rotates 90 degrees. The biomechanical phenomenon of supination => pronation of the right forearm only involves the most peripheral part of the right forearm (as the radial bone rotates around the ulna bone), and it causes the back of the right wrist and back of the right hand to rotate in a counterclockwise direction."

Jeff.

[imperfectgolfer]

This is Kirk Junge's latest comment-:

"I have explained this to you already. I think that your reading comprehension is not very good today? I said that the clubface is rotating open relative to the target line. I do not see how anyone could possibly dispute this. Please read what I have written as it is explained. This non-rotational trail arm has already been verified on 3D to my satisfaction. If you disagree then that is your problem. I am here to help people play better golf and I have thousands of happy customers. Maybe you should concentrate on your own business??"

This is my latest reply-:

"Kirk,

Here is the link to your Bryson DeChambeau swing analysis video.





Here are capture images of Bryson DeChambeau at P6.2 (image 1) and at impact (image 2).





I have drawn a blue line down the center of his right antecubital fossa and a green line along his right radial bone just above his right wrist crease.

In image 1, one can clearly see that the green line is rotated clockwise relative to the blue line (signifying a supinated right forearm alignment).

In image 2, one can clearly see that the green line is far less rotated clockwise relative to the blue line (signifying that the right forearm is far less supinated at impact than it was at P6.2).

Jeff.

[dubiousgolfer]

It would be interesting to see whether Kirk produces a 3D analysis youtube video of his swing to prove his claim.

[imperfectgolfer]

Sept 3, 2018 16:21:09 GMT -5 dubiousgolfer said:

It would be interesting to see whether Kirk produces a 3D analysis youtube video of his swing to prove his claim.

I don't expect Kirk to supply 3D evidence that Bryson DeChambeau is not rotating his right forearm in a pronatory direction in his late downswing. In fact, he has conceded that it is happening in his latest comment.

Here is his latest comment-: "I did not ever claim that Bryson setup with his right arm in a non-rotational position. He likely has less rotation than every other pro on tour, but has some due to his setup position of the arm relative to the grip."

Here is my reply to his comment.

"Where is your "evidence" that Bryson DeChambeau has less right forearm rotation than every other golfer on tour (who uses an equivalently neutral left and right hand grip)? Also, what is the biomechanical explanation that could be used to justify that "evidence-unsupported" opinion?

Where is the "evidence" that there is such an entity as a non-rotational position for the right forearm at setup that can avoid having the right forearm rotate counterclockwise in a pronatory direction during the late downswing? How is that "non-rotational phenomenon" biomechanically possible if a golfer uses a neutral left hand grip, which necessitates a PA#3 release action (based on a left forearm supinatory motion) in the late downswing in order to square the clubface by impact? If the left forearm has to rotate counterclockwise during a PA#3 release action during the late downswing (as seen in Bryson DeChambeau's swing), then how is it biomechanically possible for the right forearm to not rotate counterclockwise (in a pronatory direction) at the same time?"

Jeff.

[imperfectgolfer]

Kirk Junge has deleted my comments from the comments section under his video.

However, he cannot escape the "truth".

He correctly claims that by adopting a strong right hand grip at address, that he will have a supinated right forearm at address. He then incorrectly claims that he can maintain a non-rotated (but "fixedly" supinated) right forearm during his backswing and downswing actions - and he demonstrates that "claim" in his video while using only his right arm to move the golf club.

Here are capture images from the video.

Image 1 shows how he adopts a strong right hand grip at address. Note that his right palm is partially under the club handle and it is angled about 45 degrees relative to the ground - and that also causes the back of his right hand and the knuckles of his right hand to be angled about 45 degrees relative to the ground. Note that the clubshaft is horizontal to the ground, but it is facing the camera. Note that the toe of the club is pointing up and the clubface is vertical to the ground.

Image 2 is at the start of his backswing action. Note how the clubshaft has angled markedly to the right and how the clubface has opened about 45+ degrees relative to the ground. Note that his right palm and the back of his right hand and the knuckles of his right hand have rotated about 30+ degrees in a clockwise direction, so that they are angled about 15-20 degrees relative to the ground. What biomechanical actions are causing this clockwise rotation of the back of his right hand and his right palm - if he is not significantly changing his degree of right wrist dorsiflexion? There is only one valid biomechanical explanation - it is due to increasing right forearm supination.

Image 3 is at the end of his simulated backswing action. Note that the clubface is now wide open and parallel to the ground. Note that the back of his right hand and the knuckles of his right hand are now parallel to the ground. Note that he is holding his left palm against his right upper forearm - implying, correctly, that the upper forearm has not rotated clockwise. Note that his right palm is now parallel to the ground. What has caused his right palm, and the back of his right hand, to have rotated more clockwise between image 2 and image 3 so that they have become parallel to the ground - presuming that he is not significantly increasing his degree of right wrist dorsiflexion? There is only one valid biomechanical explanation - it is due to an increasing amount of right forearm supination.

Image 4 is at simulated impact. Note that his clubface is vertical. Note that the back of his right hand and his right palm have rotated about 45 degrees in a counterclockwise direction - compared to image 3. What biomechanical action is causing that counterclockwise rotation of his right hand? There is only one valid biomechanical explanation - it is due to right forearm pronation. Secondary proof that his right forearm is pronating by a significant amount between image 3 and image 4 is to look at the watchface area of his right lower forearm in images 3 and 4 - note that his watchface area of his right lower forearm is facing the ground far more in image 3 than in image 4.

I will donate $1,000 to any forum member, or guest, who can disprove my claims and who can come up with a more valid biomechanical explanation.

Jeff.

[dubiousgolfer]

Dr Mann

I've been looking at the Golfwrx thread concerning 'Tyler Ferrell' wrist video (url below) and wondering if you have an opinion on FWP's comments in the exchange below with golfarb1.

FWP seems to be suggesting that both forearms pronate in the backswing. Is his definition of pronation correct because I thought it was the relative movement of the radius compared to the antecubital fossa?

www.golfwrx.com/forums/topic/1681574-tyler-ferrell-wrist-video/page__pid__17869564#entry17869564

Exchange:

Fort Worth Pro, on 17 August 2018 - 10:07 PM, said:
The forearms on both arms pronate in the backswing. If the right arm were to supinate you would be too laid off. This is another measured in most players type of thing

golfarb1, on 18 August 2018 - 03:21 PM, said:
I would appreciate it if you could clarify the above comment because I am quite confused
From standard anatomy workbooks ,I understood that PRONATION of the forearm meant that the forearm rotates so the the palm faces prone(down).
If you extended both of your arms in front of you at shoulder level with both thumbs pointing up and PRONATED both forearms the palms of both hands would face prone(down).It would also mean that the thumbs would face one another and your pinky fingers or those nearest your ulnar bone would move further away from another.

Now lets take this a step further .Do the same thing,but place both palms and fingers together so that the palms and fingers are continually touching.You will find it is IMPOSSIBLE to PRONATE both forearms at the same time.But you can PRONATE your left forearm while the right forearm SUPINATES,which causes the right palm to be in a a supine position or the palm faces up.

When a golfer grips a club his hands are a position where they face one another and work together as one unit
This makes it impossible for BOTH forearms to PRONATE at the same time since PRONATION of both forearms would result in both palms facing down with the thumbs facing one another and the pinkys moving away from one another

Fort Worth Pro, on 18 August 2018 - 08:06 PM, said:
Pronation is measured as the relative movement of the ulna and the radius to each other. Not the absolute movement of the palms turning to the ground.

golfarb1, on 18 August 2018 - 08:40 PM, said
I was giving an easy to understand example of pronation with the arms directly in front of you. Changing the plane of movement does not change the definition.Both can not pronate at the same time.

Fort Worth Pro, on 18 August 2018 - 08:44 PM, said:
Don't know what to tell you. They do. Sorry man

golfarb1, Posted 18 August 2018 - 09:41 PM
I am stating that it is anatomically impossible for both forearms to pronate at the same time in the golf swing.Now if your argument is that the right forearm pronates early in the backswing and the left forearm pronates later in the backswing ,then i would have no problems in your statement


PS. Thinking a bit more deeply about this and my personal issue regarding right wrist circumduction happening at the top of my backswing (causing a pronation) and a breaking of the Right Forearm Flying Wedge.  Couldn't this mean that the LFFW seems intact but the broken RFFW will cause the clubshaft to be off -plane (ie. too steep) and if I start the downswing with a broken RFFW , I will probably be coming OTT. Could the root cause be the right hand grip being too strong , therefore the wrists are not 'orthogonal'  to each other and where a left wrist radial deviation will not assist a 'level' right wrist dorsi-flexion but could accentuate some right forearm pronation (individually for me)?

[imperfectgolfer]

Sept 6, 2018 9:47:36 GMT -5 dubiousgolfer said:

Dr Mann

I've been looking at the Golfwrx thread concerning 'Tyler Ferrell' wrist video (url below) and wondering if you have an opinion on FWP's comments in the exchange below with golfarb1.

FWP seems to be suggesting that both forearms pronate in the backswing. Is his definition of pronation correct because I thought it was the relative movement of the radius compared to the antecubital fossa?

www.golfwrx.com/forums/topic/1681574-tyler-ferrell-wrist-video/page__pid__17869564#entry17869564

Exchange:

Fort Worth Pro, on 17 August 2018 - 10:07 PM, said:
The forearms on both arms pronate in the backswing. If the right arm were to supinate you would be too laid off. This is another measured in most players type of thing

golfarb1, on 18 August 2018 - 03:21 PM, said:
I would appreciate it if you could clarify the above comment because I am quite confused
From standard anatomy workbooks ,I understood that PRONATION of the forearm meant that the forearm rotates so the the palm faces prone(down).
If you extended both of your arms in front of you at shoulder level with both thumbs pointing up and PRONATED both forearms the palms of both hands would face prone(down).It would also mean that the thumbs would face one another and your pinky fingers or those nearest your ulnar bone would move further away from another.

Now lets take this a step further .Do the same thing,but place both palms and fingers together so that the palms and fingers are continually touching.You will find it is IMPOSSIBLE to PRONATE both forearms at the same time.But you can PRONATE your left forearm while the right forearm SUPINATES,which causes the right palm to be in a a supine position or the palm faces up.

When a golfer grips a club his hands are a position where they face one another and work together as one unit
This makes it impossible for BOTH forearms to PRONATE at the same time since PRONATION of both forearms would result in both palms facing down with the thumbs facing one another and the pinkys moving away from one another

Fort Worth Pro, on 18 August 2018 - 08:06 PM, said:
Pronation is measured as the relative movement of the ulna and the radius to each other. Not the absolute movement of the palms turning to the ground.

golfarb1, on 18 August 2018 - 08:40 PM, said
I was giving an easy to understand example of pronation with the arms directly in front of you. Changing the plane of movement does not change the definition.Both can not pronate at the same time.

Fort Worth Pro, on 18 August 2018 - 08:44 PM, said:
Don't know what to tell you. They do. Sorry man

golfarb1, Posted 18 August 2018 - 09:41 PM
I am stating that it is anatomically impossible for both forearms to pronate at the same time in the golf swing.Now if your argument is that the right forearm pronates early in the backswing and the left forearm pronates later in the backswing ,then i would have no problems in your statement


PS. Thinking a bit more deeply about this and my personal issue regarding right wrist circumduction happening at the top of my backswing (causing a pronation) and a breaking of the Right Forearm Flying Wedge.  Couldn't this mean that the LFFW seems intact but the broken RFFW will cause the clubshaft to be off -plane (ie. too steep) and if I start the downswing with a broken RFFW , I will probably be coming OTT. Could the root cause be the right hand grip being too strong , therefore the wrists are not 'orthogonal'  to each other and where a left wrist radial deviation will not assist a 'level' right wrist dorsi-flexion but could accentuate some right forearm pronation (individually for me)?

FWP is 100% wrong. The right forearm has to supinate in the backswing to get the right palm to become parallel to the inclined plane by P2.5 - P3 when the intact LAFW lies on the inclined plane. The amount of supination depends on how shallow the inclined plane is between P2.5 and P3. If the right palm is parallel to the TSP (which is steeper than the elbow plane) at P3 then it will require less right forearm supination than if the right palm is parallel to the elbow plane at P3 because the elbow plane is shallower. Excessive left forearm pronation combined with excessive right forearm supination happening between P2 and P4 can cause the clubshaft to become "laid-off" (off-plane - where an imaginary line drawn out from the butt end of the cub points outside the ball-target line).

Here is an image of Martin Hall performing the backswing action - from his "metal hinges" video.

Note how Martin Hall is pronating his left forearm during his takeaway so that he can get the back of his GFLW and watchface area of his left lower forearm parallel to the inclined plane by P2.5 (image 2) and P3 (image 4).

Note that his right palm has to be parallel to the left palm (GFLW) at P3 (image 3 and also image 4 - where the intact LAFW is colored red and the RFFW is colored green). Note that the right palm is facing skywards at P3 and that requires a supinatory right forearm motion where the radial bone just above the right wrist crease is rotated clockwise relative to the right antecubital fossa.

By the way, I cannot understand your p.s. question.

Jeff.

[dubiousgolfer]

Many thanks Dr Mann - I will need to make a video of my p.s issue as its difficult for me to explain clearly in writing.

[imperfectgolfer]

Here is my further analysis of the underlying biomechanics of Kirk Junge's "non-rotational right forearm video presentation".

Consider again Kirk Junge's demonstration.

Image 1 shows Kirk's demonstration of how he adopts a strong right hand grip at address. Note how he pre-supinates his right forearm so that his right palm can get to a position that it is partially under the grip. When adopting that strong right hand grip, note how he has adopted a significantly bent (dorsiflexed) right wrist.

Image 2 shows his simulated backswing action. Note how the clubface has rotated 90 degrees open during his backswing action- while the clubshaft angles backwards away from the target. What is causing that 90 degrees clockwise rotation of the clubface?

In a previous post, I stated that the only valid biomechanical explanation was my opinion that he is increasingly supinating his right forearm during his backswing action. Is there definitive biomechanical evidence that he is increasingly supinating his right forearm as he takes the club back and is it causally responsible for all of the clubface opening?

To answer that question, consider this following explanation-:

First of all, note that his watchface on his left lower forearm is rotating clockwise about 60 degrees during his backswing action. Note that his clubface is about 20 degrees closed relative to the watchface area of his left lower forearm, signifying a slightly strong left hand grip, at address. Note that he also has an intact LAFW at address - where the clubshaft is straight-line-aligned relative to the his straight left arm. However, note that at his simulated end-backswing position (image 2), that the clubshaft is not straight-line-aligned with his left arm and it is angled slightly more towards the ground by ~20 degrees. That is due to the fact that he is slightly palmar flexing his left wrist during his simulated backswing action. Also, note that the clubface is not closed relative to the watchface area of his left lower forearm at his end-backswing position (secondary to the left wrist palmar flexion phenomenon), and that causes the clubface to be more open by about 20-30 degrees than it would otherwise be if he maintained an intact LAFW/GFLW while pronating his left forearm by ~60 degrees. In other words, part of the 90 degrees rotation of the clubface relative to the ground is due to disruption of his intact LAFW secondary to a small amount of left wrist palmar flexion and that amounts to ~20-30 degrees.

Now, consider what is happening with his respect to his right arm/forearm/hand during his simulated backswing action. There is significant evidence that he is supinating his right forearm by an additional 45+ degrees during his backswing action - note that the watchface area of his right lower forearm is angled ~45 relative to the ground in image 1 and it is seemingly parallel to the ground in image 2. I previously postulated that right forearm supination was causally responsible for all the 90 degrees of clubface rotation seen during his backswing action, but I now realize that he is likely dorsiflexing his right wrist more during his backswing action so that his right wrist is more dorsiflexed in image 2 than it was in image 1. Visual proof can be derived from two visual facts that can be seen in those capture images. First of all, note that his right wrist looks more dorsiflexed in image 2 compared to image 1 - although it is difficult to quantify how much using 2-D face-on images. Secondly, note that his clubshaft is straight-line aligned with his right forearm in image 1, but it is angled far more groundwards than his right forearm (which is angled slightly upwards) in image 2. What would cause his clubshaft to be angled more groundwards than his right forearm in image 2 (compared to image 1)? One biomechanical factor would be the ~45 degrees of increasing supination happening between image 1 and image 2. However, a second factor could be the combination of increasing right wrist dorsiflexion combined with increasing ulnar deviation - producing the clockwise roll motion of right wrist circumduction. If you look carefully at image 2, there is visual evidence suggesting that his right wrist is more dorsiflexed and more ulnar deviated - compared to its positional alignment in image 1. In particular, note that his right 2nd knuckle is closer to the ground than his 5th right knuckle (which is not surprising considering the fact that his clubshaft is angled more groundwards more than his right forearm).

In conclusion, I think that increasing right forearm supination is causally responsible for most of the clubface-opening seen in his simulated backswing action (when using only his right arm), but I now think that part of the clubface opening is due to a right wrist circumduction phenomenon secondary to the combination of "increasing right wrist extension combined with increasing right wrist ulnar deviation".

Jeff.

[dubiousgolfer]

Dr Mann - Is Kirk Junge doing that same right wrist circumduction action in his real swing rather than the demonstration where he is standing upright?

Also, is it also possible that some 'visual' rotation of the clubface in the backswing be caused by the external rotation of the upper right arm in the shoulder socket?

For example look at his elbow that seems to move into a pitch position above his right hip during his backswing at 5:29 in the below video. Doesn't that suggest external rotation happening in his right shoulder socket and could that also account for some of the opening clubface rotation?  Note that he changed the name of his swing from single axis plane to setup4impact .

[imperfectgolfer]

Sept 7, 2018 17:08:46 GMT -5 dubiousgolfer said:

Dr Mann - Is Kirk Junge doing that same right wrist circumduction action in his real swing rather than the demonstration where he is standing upright?

Also, is it also possible that some 'visual' rotation of the clubface in the backswing be caused by the external rotation of the upper right arm in the shoulder socket?

For example look at his elbow that seems to move into a pitch position above his right hip during his backswing at 5:29 in the below video. Doesn't that suggest external rotation happening in his right shoulder socket and could that also account for some of the opening clubface rotation?  Note that he changed the name of his swing from single axis plane to setup4impact .

DB,

KJ is not seemingly performing a right wrist circumduction action in his "real life" golf swing in that video. He is also not using a "non-rotation" right forearm technique (where the right forearm is "fixedly" pre-supinated by a finite amount and where it does nor pronate in the late downswing) or a zero plane shift swing action.

Here is my swing analysis-:

Backswing

Image 1 is at address where his right forearm is inline with his clubshaft. He has also pre-supinated his right forearm and he therefore has a moderately strong right hand grip at address. I have drawn a blue line along his right radial bone at the level of his lower right forearm and a red line parallel to his right 2nd metacarpal bone - and one can see that his right wrist is slightly ulnar-deviated at address.

Image 2 is at P1.5. Note that he starts his takeaway by bending his right wrist. It may "look" like his right wrist is more ulnar-deviated in image 2, but I think that's an artificial camera angle parallax issue because increasing right wrist dorsiflexion will happen in a plane that is ~45 degrees angled to the ground secondary to his pre-supinated right forearm action that gets his right forearm rotated ~45 degrees clockwise at address, and I can see no "evidence" of the clubface rolling open clockwise due to a right wrist circumduction phenomenon.

Image 3 is at P2. Note that his clubface is slightly closed relative to the watchface area of his left lower forearm, and that is expected if he adopts a slightly strong left hand grip. Note that there is no "evidence" of any clubface-opening - due either to right wrist circumduction or increasing right forearm supination. Note that the watchface area of his right lower forearm is angled slightly groundwards to the same degree at P2 as it was at P1.

Image 4 is nearing-P3 (roughly mid-backswing). Note that his clubface is opening significantly. What is causing the clubface-opening phenomenon? It is obviously due to the fact that he is rolling his left forearm clockwise using a left forearm pronatory action that gets his clubshaft parallel to his "desired" mid-backswing plane (which is slightly steeper than the elbow plane). Note that the radial bone area along his right lower forearm is obviously more clockwise rotated relative to his right antecubital fossa - secondary to a right forearm supination phenomenon - compared to image 1 and image 2 and image 3. Secondary proof that he has increased his degree of right forearm supination is to note that the watchface area of his right lower forearm is more horizontally parallel to the ground at P3 than it was at P1 (image 1). Note that his right palm is parallel to the inclined plane on which his clubshaft is located and it is under the club handle. I believe that it is only biomechanically possible to achieve that right palm alignment at P2.5 - P3 if he increasingly supinates his right forearm.

Image 5 is at P4. Note that his clubshaft is on a slightly steeper plane - probably just below the TSP. His right forearm is still supinated, but less than it was at P3 (where his clubshaft was on a shallower plane).

Downswing

Image 1 is at P5.5. Note how much he has shallowed the clubshaft between P4 and P5.5. Note that the clubface is still wide open and there is no evidence that he is closing the clubface relative to the clubhead arc. I have drawn a red line along the radial bone area of his right lower forearm, and it is obviously rotated a lot clockwise relative to his right antecubital fossa - and that means that his right forearm is markedly supinated at P5.5, which is biomechanically necessary if he wants to get his right palm in that position where it is under the club handle and parallel to a shallower plane. Note that he does not have an intact LFFW and his clubshaft is tracking under the plane of both his left forearm and his right forearm - and that is due to the fact that he is slightly bowing his left wrist. His clubshaft is seemingly tracking along a shallower plane than it was in image 4 of his backswing action - where he seemingly had an intact LFFW where the clubshaft was tracking closer to the plane of his right forearm (and not along a plane that is significantly shallower than the plane of his right forearm).

Image 2 is at P6+ (just bypassing P6). Note how much his clubshaft is angled towards the ground and it not parallel to the ground at P6. Note that his clubface is now closing relative to the clubhead arc. Why? The answer is obvious - look at how much he has supinated his left forearm between image 1 and image 2. Also, note that his radial bone along his right lower forearm is significantly less clockwise rotated relative to his right antecubital fossa in image 2 when compared to image 1, and that means that he is pronating his right forearm. Secondary proof that he is pronating his right forearm is to look at the back of his right hand and right palm - note how much they have rotated clockwise in a pronatory direction between image 1 and image 2. I think that KJ's "non-rotation" claim that his right forearm does not pronate in his late downswing is 100% false.

Image 3 is at impact. His right palm is behind the club handle and his right forearm is obviously more pronated at impact than it was in image 1.

Regarding your question as to whether external rotation of the right humerus has a clubface-opening effect - I can think of no reason why it should have any clubface-opening effect. Use a short club (like the short club I use in my videos) and mimic KJ"s P2 position where the clubface is not open to the clubhead arc. Then, externally rotate your right humerus 30 - 40 degrees while avoiding any increasing right forearm supination - your clubface should not open more relative to the clubhead arc as the right forearm/right wrist/right hand/clubshaft rotates as a single unit.

Jeff.