Analysing the controversial AMG video

[dubiousgolfer]

Dr Mann

I have emailed Dr Kwon and Dr Mackenzie but I don't think replies will be forthcoming because they haven't replied to my previous emails (maybe they are too busy).

I'm not sure Dave Tutelman is an expert on this type of question but I will email him if Dr Kwon and SMK do not reply.

DG

[imperfectgolfer]

I have a new theory on why the linear force being applied at the level of the left hand on the club handle is highest between P5.5 => P6.2 even though the lead hand speed reaches its maximum value at ~P5.5.

Consider DJs' downswing between P4 => P5.5.

Note that DJs' lead hand goes mainly downwards between P4 => P5.5 due to the pivot-induced release of PA#4 and the lead arm speed reaches its maximum speed at ~P5.5. Note that his lead hand is outside his trail thigh at P5.5 and it is no closer to the target at P5.5 than it was at P4.

From that position, he needs to change the direction of his hand arc path so that it moves targetwards and that requires lot of force that is initially directed targetwards and then slightly more upwards just prior to impact.

Here is Kwon's graph showing the lead hand direction force and its magnitude - represented by the black arrows.

Note that the black arrow force is small between P4 => P5.5 because it does not take much force to move the lead arm groundwards. However, note that the black arrow force is increased at P5.5 and even more at P6 and it is also directed more targetwards. I think that it takes a lot of force - operating at the level of the lead hand on the club handle - to change the direction of motion of the butt end of the club between P5.5 => P6.2 when the club handle is already traveling at its fastest speed at P5.5 in a downwards direction. I suspect that the force needed to change the direction of the butt end of the club from being directed downwards to being directed targetwards is mainly derived from the upwards motion of the lead shoulder socket - happening when the lead leg straightens and elevates the lead side of the pelvis and when the lead mid-torso area lengthens (stretches -out) thereby elevating the lead shoulder socket.

Jeff.

[dubiousgolfer]

Dr Mann

You wrote "Here is Kwon's graph showing the lead hand direction force and its magnitude - represented by the black arrows".

Just to clarify, the black arrow is not just the lead hand force but the mid-hand net force that theoretically could be applied by both hands.

DG

[dubiousgolfer]

Here is SMK's reply to me:

"Forces would be generated instantaneously throughout the body.

Here’s is something you can try yourself. Grab two light dumbbells (say 10 lbs). Flex your elbows so you feel muscles in you’re arms and shoulders working. Now go into a half squat and pause. While in that squat ask yourself where the force is coming from that holding the dumbbells in the air.

What muscles increased their activation level the most from 5.5 to 6.2? I would say a combo of lead and trail shoulder."


DG

[imperfectgolfer]

DG,

You wrote-: "Just to clarify, the black arrow is not just the lead hand force but the mid-hand net force that theoretically could be applied by both hands."

I have no reason to believe that the trail hand is applying any force between P5.5 => P6.2 that would increase the "linear force being applied by the lead hand" that SMK describes in his vimeo-video, and which causes the lead hand to move the club handle along the hand arc path.

Neither SMK or Kwon have ever described the trail hand as being instrumental in moving the lead hand down the hand arc path. They have only described the trail hand working as couple.

Jeff.

[imperfectgolfer]

Feb 28, 2023 20:58:39 GMT -5 dubiousgolfer said:

Here is SMK's reply to me:

"Forces would be generated instantaneously throughout the body.

Here’s is something you can try yourself. Grab two light dumbbells (say 10 lbs). Flex your elbows so you feel muscles in you’re arms and shoulders working. Now go into a half squat and pause. While in that squat ask yourself where the force is coming from that holding the dumbbells in the air.

What muscles increased their activation level the most from 5.5 to 6.2? I would say a combo of lead and trail shoulder."


DG

What would the trail shoulder be doing to increase the lead hand's "linear force" that is reaching its maximum value between P5.5 => P6.2?

I think that SMK's comment about dumbells is unhelpful.

Jeff.

[imperfectgolfer]

I have further evidence to support my new "idea" that the lead hand's linear force as measured on the club handle, which reaches its maximum value between P5.5 => P6.2, is due to the elevation of the lead shoulder socket.

Here is a BBG video.





At the 3:48 minute time point, they present the Swing Catalyst results of Dustin Johnson's driver swing.

Here are the results.

This is the start of the downswing at P4.

Note that his horizontal GRF value (magenta graph) is at its peak (see small circle). Note that he is not producing much rotary torque (yellow graph) or any vertical GRF (cyan graph).

This image is at P4.5 - note that his rotary torque is now at its peak. That makes sense because he is now starting to perform his hip-squaring action (which is due to a counterclockwise pelvic rotation) and torque must momentarily precede motion.

Note that he is producing only a small amount of vertical GRF under his lead foot at P4.5.

This image is at P5.2.

Note that this is the time point when his vertical GRF under his lead foot is peaking.

From this point onwards, DJ is going to soon be straightening his lead leg and elevating his lead shoulder socket starting at ~P5.3 - P5.5 and that will cause his vertical GRF to diminish thereafter.

This image is at impact.

Note that his vertical GRF measurement is now below zero and that he has only 9% of his overall COP measurement under his lead foot - which means that DJ is a reverse foot golfer.

What these graphs show is that DJ increases his vertical GRF under his lead foot to its maximum value at P5.2 so that he can start to straighten his lead leg and elevate his lead shoulder socket soon thereafter at ~P5.3 - P5.5. The elevation of his lead shoulder which continues between P5.5 => P6.2+ provides the "force" needed to allow him to maximise his lead hand's linear pulling force on the club handle between P5.5 => P6.2. In other words, the "force" comes from the pivot action causing elevation of the lead shoulder socket and it is not due to any independent lead arm/hand motion. There is also no need to conjure a theory that the shoulder girdle muscles are causally responsible for producing this "force" that happens between P5.5 => P6.2+.

Jeff.

[dubiousgolfer]

Dr Mann

I think you made a typo because that is Drew Cooper not DJ.

I think SMKs major winner is JT because he's used him in other videos on vimeo, therefore I've shown 2 images of him at P5.5 and P6.2 below with the similar frame images from SMk's video.





Your bolded remarks could be possible but I don't think its probable because I tried to test this out myself on a very slippery table. I put my chest flat against the table such that my lead arm was lying horizontal and at an angle of 45 degrees to my chest. Then pushed hard against the table with my right arm , plus using increasing assisting force via my legs/feet to accelerate my chest & shoulder sockets away from the table. There was hardly any torque (MOF) acting on my arm to create any tangential linear force that could recreate the magnitudes seen in those orange arrows on JT images (note that the net forces in purple are even greater in magnitude and their directions not very vertical).

251N force at P5.5 is about 56 lbs-force while 351N at P6.2 is about 79 lbs-force, therefore it doesn't seem possible to create such a large MOF just by the vertical motion of the shoulder socket.

Further, if you look at some of the EMG research, there is a significant activation of the shoulder girdle muscles in what they define as the forward swing from P4-P6 and acceleration phase from P6-P7

Here are the EMG graphs of 13 pros back in 1993 (I don't have the full research article but I managed to find the graphs).

Electromyographic analysis of the shoulder during the golf swing (Marilyn Pink, MS, PT, Frank W. Jobe, MD, and Jacquelin Perry, MD).



The graphs can be seen clearer using this link below

www.semanticscholar.org/paper/Electromyographic-analysis-of-the-shoulder-during-Pink-Jobe/56ace45146ebeee863eb9b2af3c36f7258ccf37f

Just click on the figures 1- 8 in the above link and it brings up a magnified image of each graph.

DG

[imperfectgolfer]

Mar 1, 2023 10:47:26 GMT -5 dubiousgolfer said:

Dr Mann

I think you made a typo because that is Drew Cooper not DJ.

I think SMKs major winner is JT because he's used him in other videos on vimeo, therefore I've shown 2 images of him at P5.5 and P6.2 below with the similar frame images from SMk's video.





Your bolded remarks could be possible but I don't think its probable because I tried to test this out myself on a very slippery table. I put my chest flat against the table such that my lead arm was lying horizontal and at an angle of 45 degrees to my chest. Then pushed hard against the table with my right arm , plus using increasing assisting force via my legs/feet to accelerate my chest & shoulder sockets away from the table. There was hardly any torque (MOF) acting on my arm to create any tangential linear force that could recreate the magnitudes seen in those orange arrows on JT images (note that the net forces in purple are even greater in magnitude and their directions not very vertical).

251N force at P5.5 is about 56 lbs-force while 351N at P6.2 is about 79 lbs-force, therefore it doesn't seem possible to create such a large MOF just by the vertical motion of the shoulder socket.

Further, if you look at some of the EMG research, there is a significant activation of the shoulder girdle muscles in what they define as the forward swing from P4-P6 and acceleration phase from P6-P7

Here are the EMG graphs of 13 pros back in 1993 (I don't have the full research article but I managed to find the graphs).

Electromyographic analysis of the shoulder during the golf swing (Marilyn Pink, MS, PT, Frank W. Jobe, MD, and Jacquelin Perry, MD).



The graphs can be seen clearer using this link below

www.semanticscholar.org/paper/Electromyographic-analysis-of-the-shoulder-during-Pink-Jobe/56ace45146ebeee863eb9b2af3c36f7258ccf37f

Just click on the figures 1- 8 in the above link and it brings up a magnified image of each graph.

DG

Thanks for the typo correction re: Drew Cooper.

That research paper on shoulder girdle activation apparently does not distinguish between isometric versus isotonic contraction, and it is difficult to know to what degree the shoulder girdle muscles play a role in moving the lead hand targetwards between P6 => P7. Also, when I refer to elevation of the shoulder socket, it not only moves upwards but also away from the target if the golfer develops secondary axis tilt/right lateral bend in the later downswing. Back muscles may therefore also be in play, together with the lead shoulder girdle muscles, in providing the energy to move the lead humeral head in a direction that is both upwards-and-away from the target.

I don't know how to solve the problem of which is the major biomechanical factor responsible for providing the necessary "force", but I now think that applying the optimum amount of "force" to the lead hand, which is pulling the club handle between P5.5 => P6.2, is a very important component of a pro quality golf swing action. I previously paid most of my attention to the biomechanics causing the release of PA#4, and I previously never thought deeply about the large amount of "force" needed between P5.5 => P6.2+ in order to change the direction of motion of the butt end of the club handle.

By using Drew Cooper as an example I am inferring that generating a large vertical GRF under the lead foot at P5.2 is a very important factor in generating that "force". However, that may not be true because some PGA tour golfers generate very little vertical GRF and still drive the ball >300 yards. It is possible that they mainly use their trunk/back and lead shoulder girdle muscles to provide that "force".

Jeff.

[dubiousgolfer]

Dr Mann

I am checking a few things regarding the vertical forces that can be created by golfers. For example, Matthew Wolff can actually create a vertical ground force of 324 lbs-force over and above his rest weight. That's a huge force, much greater than the experiment I did with my lead arm on a table.

DG

[dubiousgolfer]

Looking at this Drew Cooper Swing Catalyst screen image where his vertical ground reaction force is close to maximum value, doesn't make any sense to me.



The graph peaks at 2045 lbs-force , so I assume that is a calibration problem because it is equivalent to 146 stones-force.

However, there is a value further to the right showing Max Weight 219%/ 461 lbf.

Therefore, he is exerting an extra maximum vertical ground reaction force of 119% over and above his rest weight (ie. 100%) which is:

(461/219)*119% = 251 lbf = 18 stone-force

This is a huge force equivalent to 1117 Newtons approx .

But is it possible for such a vertical ground reaction force to perpetuate through the golfers body up to his lead shoulder socket? If yes, then it might be possible to create an MOF on the COM of the 'arms/club' unit to create those linear hand path forces depicted in SMK's video from P5.5-P6.2 .

I'm unsure if anyone will be able to prove whether it's possible or not.

DG

PS.  I've done some general maths on the vertical force required at lead shoulder socket to recreate the linear force 251.8N in SMK's P5.5 screen image,  and calculated an approximation of 710 N.

There is also the increased tension pull by the club on the hands/arms as it releases which may add another 400 N (generally downwards) that the shoulder socket force would need to cope with. So it would need to exert 710 + 400 = 1110 N  vertical force which is still below Drew Cooper's 1117 N. 

I've struck through the above because the club shaft at P5.5 is not in the downwards direction, therefore no extra shoulder vertical force required to offset against the 'pull' of the club on the hands/arms. But there will be when the club reaches P6.2 position because the club shaft will be pulling at about 240 N so maybe another extra 170 N vertical force required at lead shoulder socket level which would be 2066 + 170 = 2236 N . still reasonably below Drew Coopers 1117 maximum vertical ground reaction force

The 2066 value was the shoulder socket force required (using some general maths) to create the 351 N linear hand force at P6.2.

The maths was tricky for me and I've made a few errors on the way but at P6.2 position my calculations now show that the shoulder socket force required is almost double the max vertical ground reaction force that Drew Cooper was capable of.

[imperfectgolfer]

DG,

Your analysis and questions are too technical for me to understand/answer.

Perhaps you could contact Dr. Scott Lynn of Swing Catalyst to answer your questions.

Jeff.

[dubiousgolfer]

Dr Mann

Yes it is quite technical and I sent an email to Dr Scott Lynn yesterday.

One thing I've realised is that I cannot cross reference the 'Swing Catalyst' graphs vs SMK's 'Force path' graphs because of time delays in their measurements. The grf graphs are measured between feet and force plates, and any influence they might have on assisting the materialisation of linear hand forces would take time. 

DG

[imperfectgolfer]

DG,

I know that you have a strong penchant for reducing golf swing biomechanical motions to a physics problem, and although it is sometimes useful., I cannot imagine it being useful in this scenario.

You are attempting to establish a connection between two facts - i) the vertical GRF magnitude and ii) the linear force being exerted on the club handle by the lead hand at P5.5 and P6.2. However, there are many confounding variables that you are not taking into account.

First of all, you are dealing with a dynamic situation where the club handle is in constant motion and at P5.5 it has reached its maximum speed, and it thereby has considerable momentum, which must surely affect the amount of force needed to move it further down the hand arc path. Secondly, there are other biomechanical factors that affect the upward motion of the lead shoulder socket between P5.5 => P6.2+ - use of the lead shoulder girdle muscles and back muscles. Thirdly, there is the unanswered question as to whether the motion of the trail hand can provide some of the force needed to move the lead hand hand further along the hand arc path.

Here is Gary Woodland's Swing Catalysts graphs

Note that he generates very low vertical GRF values, but he is capable of driving a golf ball a long distance and he is one of the longest drivers in the PGA tour.

He is not a "jumper " and he mainly relies on body rotation to generate swing power.

He looks a front-foot golfer who is rotating very well through impact. I think that his lead shoulder elevation could mainly be due to muscle power (related to his use of back muscles/peri-scapular muscles) and the development of secondary axis tilt and right lateral bend that causes his shoulder sockets to rotate more like a ferris-wheel through impact.

Jeff.

[dubiousgolfer]

Feb 28, 2023 19:39:11 GMT -5 imperfectgolfer said:

I have a new theory on why the linear force being applied at the level of the left hand on the club handle is highest between P5.5 => P6.2 even though the lead hand speed reaches its maximum value at ~P5.5.

Consider DJs' downswing between P4 => P5.5.

Note that DJs' lead hand goes mainly downwards between P4 => P5.5 due to the pivot-induced release of PA#4 and the lead arm speed reaches its maximum speed at ~P5.5. Note that his lead hand is outside his trail thigh at P5.5 and it is no closer to the target at P5.5 than it was at P4.

From that position, he needs to change the direction of his hand arc path so that it moves targetwards and that requires lot of force that is initially directed targetwards and then slightly more upwards just prior to impact.

Here is Kwon's graph showing the lead hand direction force and its magnitude - represented by the black arrows.

Note that the black arrow force is small between P4 => P5.5 because it does not take much force to move the lead arm groundwards. However, note that the black arrow force is increased at P5.5 and even more at P6 and it is also directed more targetwards. I think that it takes a lot of force - operating at the level of the lead hand on the club handle - to change the direction of motion of the butt end of the club between P5.5 => P6.2 when the club handle is already traveling at its fastest speed at P5.5 in a downwards direction. I suspect that the force needed to change the direction of the butt end of the club from being directed downwards to being directed targetwards is mainly derived from the upwards motion of the lead shoulder socket - happening when the lead leg straightens and elevates the lead side of the pelvis and when the lead mid-torso area lengthens (stretches -out) thereby elevating the lead shoulder socket.

Jeff.

Dr Mann

I think your theory above is pretty close . 

The reason for the increased force from P5.5-6.2  is because the COM of the club is moving away from target at P5.5  , therefore DJ is having to apply extra force on the grip to both change the COM direction targetward plus add some clubhead speed. 

What confused me was the fact that there was an increase in that hand path linear force from P5.5-6.2 while the grip end was slowing down . I hadn't taken into account that the COM of the club was moving away from target and creating tension in the club shaft , pulling against DJ's hands (which he'd need to overcome) while he changed his hand path targetward.

With regards the possible ways to create those forces, I've calculated that it would require too huge a vertical force on the shoulder socket to create those linear hand path forces (via some induced MOF on the 'arms/club' unit). So it does seem that the use of the back and shoulder girdle muscles are creating those forces.

DG