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Post by imperfectgolfer on Feb 26, 2021 1:15:02 GMT -5
Here is the reply I received from Dr Kwon concerning those images for Fig 1A and 1B "On Thu, Feb 25, 2021 at 5:55 PM <kwon3d@kwon3d.com> wrote: The images do not show the actual forces. They just show the concept of net force/moment: reduction of multiple eccentric forces to a net force and a net moment. ^_^ Cheers, Young-Hoo Kwon, Ph.D. Biomechanics & Motor Behavior Laboratory Texas Woman’s University P. O. Box 425647 Denton, TX 76204-5647, USA ykwon@twu.edu | kwon3d@kwon3d.com DG His reply is exactly how I have always interpreted his images. Jeff.
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Post by dubiousgolfer on Feb 26, 2021 10:06:03 GMT -5
The images below is how I've deciphered the Koike and Choi graphs (one might have to magnify the images on the screen to see the direction of rotation of the red arrows- apologies). DG
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Post by imperfectgolfer on Feb 26, 2021 10:23:24 GMT -5
I don't understand the last post.
Where are the graphs? What is the source of those images and text?
Jeff.
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Post by dubiousgolfer on Feb 26, 2021 18:20:44 GMT -5
The image avatars I captured from Gears videos and then I added the 'straight(force) arrows and curved (torque rotation) arrows in myself. The individual hand forces graph for Koike is (a) below , while the individual hand torque graphs is (c). The 'early-mid' downswing individual hand force graphs for Choi is A and E below . The 'early-mid downswing' individual hand torque graphs are 'N' and 'R'. The text is my attempt at deciphering the graphs (right or wrong). DG
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Post by imperfectgolfer on Feb 26, 2021 22:44:32 GMT -5
I don't have the mental ability to understand those Koike/Choi graphs.
Jeff.
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Post by dubiousgolfer on Feb 27, 2021 6:06:51 GMT -5
I don't have the mental ability to understand those Koike/Choi graphs. Jeff. I must admit that it's very difficult to understand as one has to : 1. Conceptualise how the 'coordinate system axis' is rotating in space when fixed to the club (this applies specifically to the Choi graphs). The coordinate system for Koike wasn't fixed to the club but within the instantaneous swing plane. 2. Understand vectors associated with 'Torques' and get acquainted with the 'Right Hand Rule ' (which defines the direction of rotation in the plane perpendicular to the Torque vector). This applies to both Choi and Koike graphs. DG
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Post by imperfectgolfer on Feb 27, 2021 10:18:49 GMT -5
I am hoping that we get many more instrumented grip study results in the next 1 - 2 years, so that this issue can be better understood. It may help me better understand the forces/torques operating at the level of the hands on the grip.
Jeff.
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Post by dubiousgolfer on Mar 3, 2021 23:37:49 GMT -5
Dr Mann I have an alternative theory about the hand forces and have edited Dr Kwon images below. DG
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Post by imperfectgolfer on Mar 4, 2021 10:37:22 GMT -5
DG,
I think that your modified image correctly describes the force, and its direction, produced by the left hand as part of the hand couple phenomenon. However, Kwon's image shows that the left hand is producing a linear lead hand pulling force that is directed downwards-and-slightly outwards - where the downwards component is the tangential component of the left hand's pulling force and the outward component is the radial component of the left hand's pulling force.
Jeff.
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Post by dubiousgolfer on Mar 4, 2021 11:14:58 GMT -5
Dr Mann I do agree that your biomechanical reasoning below to explain the right hand force makes perfect logical sense " The combination of the right shoulder socket's motion away from the target that is due to the biomechanical effects of i) and ii), which is combined with the right forearm angle becoming increasingly more horizontal due to his efficient right arm adduction maneuver that is combined with a pitch elbow motion of the right arm, should enable Dustin Johnson to produce a small degree of positive force-across-the-shaft with his right hand - even though he is not changing his right elbow bend angle, or changing his degree of right wrist extension or his degree of right wrist upcocking. " I can also imagine that there is a possibility that the left hand force might tally with the Dr Kwon's graph (ie. with the black arrow net force direction relative to the shaft). But in reality I cannot see how that lead hand force direction can be possible in JS or DJ swing from P4-P5. DG
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Post by dubiousgolfer on Mar 8, 2021 19:55:33 GMT -5
Here is a graph of the forces applied by the fingers and thumbs of each hand for 2 scratch golfers 'a' and 'v' from the research article below. www.researchgate.net/publication/28577829_Measurement_and_analysis_of_grip_force_during_a_golf_shotI was interested specifically in graphs B and C below that relate to sensor force values for their left and right hands respectively. I did my best to identify each 'finger force' graph using pointer arrows to identify to them: LT = left thumb LIF= left Index finger LMF = left middle finger LRF= left ring finger LLF= left little finger LP= left palm RT = right thumb RIF= right Index finger RMF= right middle finger RRF= right ring finger RLF= right little finger RP= right palm I then looked at their approximate magnitude comparisons in the early downswing and tried to represent the force vectors for each finger/thumb in the picture below (red arrows relate to left hand while yellow arrows relate to the right hand). Top graph is golfer (a) while bottom graph is golfer (v). I didn't add in the palm forces as I couldn't be certain of the direction so just used the fingers and thumbs as a first approximation. All I can tentatively surmise from the force graphs and image above is: 1. That the left fingers and thumb are providing a positive torque 2. That the right hand is not providing much torque at all and that the forces are directed mostly in one direction across the shaft (almost like DT's previously posted image). Obviously , I could be wrong but thought I'd give it a try. DG PS. On reflection , there is no way I can assume the direction of those finger forces as they probably are a measure of pressure forces applied by different areas of the fingers around the grips rounded surface. The thumb pressure forces might be okay but note that for golfer 'v' there was no right thumb force graph.
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Post by imperfectgolfer on Mar 8, 2021 23:05:25 GMT -5
I think that those are measurements of grip forces exerted by the hands on the club handle, and they do not reflect forces on the club handle due to the release of PA#4 or due to hand couple forces.
Jeff.
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Post by imperfectgolfer on Mar 8, 2021 23:08:31 GMT -5
Dr Mann I do agree that your biomechanical reasoning below to explain the right hand force makes perfect logical sense " The combination of the right shoulder socket's motion away from the target that is due to the biomechanical effects of i) and ii), which is combined with the right forearm angle becoming increasingly more horizontal due to his efficient right arm adduction maneuver that is combined with a pitch elbow motion of the right arm, should enable Dustin Johnson to produce a small degree of positive force-across-the-shaft with his right hand - even though he is not changing his right elbow bend angle, or changing his degree of right wrist extension or his degree of right wrist upcocking. " I can also imagine that there is a possibility that the left hand force might tally with the Dr Kwon's graph (ie. with the black arrow net force direction relative to the shaft). But in reality I cannot see how that lead hand force direction can be possible in JS or DJ swing from P4-P5. DG I think that your composite image of DJ shows a hand arc path between P4 => P5 that is downwards and away-from-the-target, and I think that it will produce the left hand forces seen in Kwon's diagram. Jeff.
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Post by dubiousgolfer on Mar 9, 2021 10:23:52 GMT -5
I think that those are measurements of grip forces exerted by the hands on the club handle, and they do not reflect forces on the club handle due to the release of PA#4 or due to hand couple forces. Jeff. Dr Mann I'm not sure I understand what you mean. The sensors just measure force via whatever is pressing against it (ie. the hands) so that should involve all forces that are transmitted via the hands (ie. also via the 'legs/torso/arms/hands'). With regards JS frame images and whether his left/right hand forces align with Dr Kwon's image , I have rotated Dr Kwon's image to match frames 1-4 for JS's downswing. If those green and blue force arrows represent the total forces applied to the grip via the hands why is the grip going downwards along the hand path? Where is the 'Hand Path Force' required to do linear work on the club? DG
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Post by imperfectgolfer on Mar 9, 2021 10:43:34 GMT -5
DG, You wrote-: " I'm not sure I understand what you mean. The sensors just measure force via whatever is pressing against it (ie. the hands) so that should involve all forces that are transmitted via the hands (ie. even via the legs/torso/arms/hands)." The sensors may measure all the forces, but it cannot differentiate forces solely due to finger gripping from forces causing the release of PA#4. Regarding Kwon's image, I perceive that it was only reflective of a single moment in time - somewhere around P5 - P5.2. At P4 - P4.2 in Jamie Sadlowski's swing, the green arrows should be directed more towards the butt end of the club. I think that the following Kwon image better reflects the direction of the lead hand force at different time points in the downswing - represented by the black arrows, and that linear hand force can be divided into tangential (green arrow) and radial (blue arrow) forces. Note where the black arrow is directed at P5 - outwards and slightly downwards. Jeff.
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