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Post by imperfectgolfer on Dec 24, 2019 10:17:57 GMT -5
S,
You wrote-: "There are studies that show that the right hand pressure of the elite golfer decreases to about zero by impact."
Please post a link to those studies as I have never seen such a study (other than the Koike study).
Jeff.
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Post by dubiousgolfer on Dec 24, 2019 11:50:45 GMT -5
Dr Mann I've been looking at the graphs by Koike (Instrumented Grip ) for his 2006 research. The graphs are shown below: For clarification here are the graphs you posted previously relating to that same paper I'm assuming the 'Head-side hand' is the right hand, while the 'Butt-side hand' is the left hand (ie. the dashed line). Tutelman says the following: "Graph (a) shows the force across the shaft by each hand individually, the pull by the left hand and push by the right hand. (Actually, it's measured as a push either way; the mostly negative dotted curve says the left hand force is a pull until almost impact.) They are nearly equal the whole duration of the downswing, and comprise a couple almost perfectly. The forces cross about 20% of the downswing time before impact, and form a negative couple of about 10 Nm at impact."
"Graph (c) shows the couple produced by each hand individually. For instance the dotted curve shows the left-hand couple; the left thumb is pushing and the left pinky is pulling. Similarly for the right hand and the solid curve. By the time you get to impact, the right hand provides only a tiny couple, perhaps fractionally positive, and the left is negative about 10 Nm."The problem with Koike's experiment is that the golfer had to use a split grip , therefore the 'individual' couples produced by each hand might be different to a golfer who uses an overlapping grip. Also we don't really know what strength of grip the golfer used so I don't think we can assume graph c is some generic representation of a pro-golfers swing. You mentioned Koike's research was flawed in a previous post below: "I would take the argument further and assert that Koike's measurement system is also flawed because he uses a split-hand grip where he presumes that the right hand is only pushing against the shaft when it could be pushing against PP#1 (located over the base of the left thumb). I would need to see the results of many more research studies using an instrumented grip before I take the hand-couple theory seriously. I would also need to see how Sasho's hand-couple theory affects the way a golfer performs the downswing from a biomechanical perspective, and I have never seen Sasho comment on this issue."But graph 'a' definitely shows a net 'negative couple'. Koike repeated his experiment in 2016 and the force graph below also shows a negative couple by impact. Again graph 'a' shows a net negative couple by impact while graph 'c' shows virtually zero right hand couple , but definitely negative left hand couple. Graph 'c' again cannot be regarded as a generic representation of what is happening in each hand (with regard to individual hand couples) because the golfer is using a split grip (as mentioned before). Am I correct in my assumptions above? DG
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Post by imperfectgolfer on Dec 24, 2019 12:58:30 GMT -5
DG,
My only point of contention with what you have written applies to graph (c) that refers to the Z axis, which is an off-plane motion (beta torque motion). Theoretically, a skilled golfer should not be applying a beta torque motion if his clubshaft is on-plane, which may account for the fact that the measured forces in graph (c) are so small. I would therefore discount the relevance of graph (c) to the topics we have discussed in this thread.
You stated that DT wrote-: "Graph (c) shows the couple produced by each hand individually. For instance the dotted curve shows the left-hand couple; the left thumb is pushing and the left pinky is pulling. Similarly for the right hand and the solid curve. By the time you get to impact, the right hand provides only a tiny couple, perhaps fractionally positive, and the left is negative about 10 Nm."
I have no idea what he is talking about!!! At impact, those hand forces in graph (c) are working in the Z plane, which is a beta torque plane that only affects the accumulator #3 angle at impact.
Graph (a) does show that any push-pressure exerted by the right hand in the alpha torque plane at impact is negligible (and probably negative), and I agree with you that it is compatible with a negative hand couple phenomenon happening at impact.
Jeff.
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Post by syllogist on Dec 24, 2019 14:47:02 GMT -5
Dr. Mann, It was in the mid-2000s that I ran across the grip pressure study. Can't find it now. However the attached shows graphic results for one tour golfer where peak right hand grip force was 0.05 sec. before impact (onset of release) and then fell sharply up to impact. therecreationalgolfer.com/blog/2016/12/more-on-grip-pressure/S
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Post by dubiousgolfer on Dec 24, 2019 18:36:53 GMT -5
DG, My only point of contention with what you have written applies to graph (c) that refers to the Z axis, which is an off-plane motion (beta torque motion). Theoretically, a skilled golfer should not be applying a beta torque motion if his clubshaft is on-plane, which may account for the fact that the measured forces in graph (c) are so small. I would therefore discount the relevance of graph (c) to the topics we have discussed in this thread. You stated that DT wrote-: " Graph (c) shows the couple produced by each hand individually. For instance the dotted curve shows the left-hand couple; the left thumb is pushing and the left pinky is pulling. Similarly for the right hand and the solid curve. By the time you get to impact, the right hand provides only a tiny couple, perhaps fractionally positive, and the left is negative about 10 Nm." I have no idea what he is talking about!!! At impact, those hand forces in graph (c) are working in the Z plane, which is a beta torque plane that only affects the accumulator #3 angle at impact. Graph (a) does show that any push-pressure exerted by the right hand in the alpha torque plane at impact is negligible (and probably negative), and I agree with you that it is compatible with a negative hand couple phenomenon happening at impact. Jeff. Dr Mann You are correct that graph (c) refers to the z axis but imho the individual hand torque vectors will also point in the z-axis (either positive or negative). This is related to something called the 'Right Hand Rule ' in physics. The video below explains it quite well even though I find its presentation unnecessarily juvenile. Therefore graph 'c' in Koike's research article of 2006 , the golfers left hand (dashed line) is showing a 'negative' torque vector approaching impact (which will be pointing into the screen/page, -z axis direction, from a face-on view). This means the left hand will be moving 'clockwise' from a face-on view as the club approaches impact. The golfers right hand moves close to a 'zero torque' by impact. In reality , it is very slightly positive which means its 'Moment of Force' or Torque vector will be pointing out of the screen/page (ie. positive z-axis direction) from a face-on view . The rotation of the right-hand will be negligible in the anti-clockwise direction from a 'face-on' view. DG PS. I still don't understand DT's statement below regarding the right hand if my comments above are correct . Unless he means that the right hand's thumb is slightly pushing and left pinky slightly pulling closer to impact (but that would be assuming a very strong right hand grip ). I say this because for most of the downswing the right hand is showing a negative torque so how could the golfer be pushing with the thumb and pulling with the pinky (which is a positive torque)? It would be nice to have seen video swings of the individual golfers in the 2006 and 2016 research. I did email Koike asking for the golfers names or possible swing video footage about a year ago but he didn't reply back. ""Graph (c) shows the couple produced by each hand individually. For instance the dotted curve shows the left-hand couple; the left thumb is pushing and the left pinky is pulling. Similarly for the right hand and the solid curve. By the time you get to impact, the right hand provides only a tiny couple, perhaps fractionally positive, and the left is negative about 10 Nm."
Imho, the 2 golfers used must have demonstrated different swing biomechanics and maybe the 1st one was using more of a pitch right elbow (ie. negative right hand torque) TGM swinging action while the other more of a swing/hitting action (maybe more PA1). Whatever the assumed swing actions, there must have been forward shaft bend happening into impact which accounts for the net negative torque.
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Post by syllogist on Dec 25, 2019 6:27:24 GMT -5
DG,
Forward shaft bending aside, if the hands slow during release, does that not show that a net negative torque is acting on the hands?
S
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Post by imperfectgolfer on Dec 25, 2019 12:16:02 GMT -5
DG, Forward shaft bending aside, if the hands slow during release, does that not show that a net negative torque is acting on the hands? S I must admit that I get very annoyed by your posts because I perceive them to be very nonsensical/irrational and therefore unhelpful. If the left hand slows down during the late downswing, what does it help to state that "a negative torque is acting on the hands"? Are you talking about the left hand slowing down because the left arm is slowing down or are you talking about the relationship between the left hand as it relates to the clubshaft due to motion happening at the level of the left wrist joint? If the left arm slows down due a decreased amount of positive torque happening at the level of the left shoulder socket in a TGM swinging action, then the cause-and-effect relationship refers to the left arm (and not the hands) relative to the upper torso. A negative torque phenomenon happening at the level of the left shoulder socket means that the left arm is rotating faster than the torso. A positive torque phenomenon happening at the level of the left shoulder socket means that the left shoulder socket has more angular velocity than the left arm (as obviously exists when PA#4 is being actively released in a TGM swinging action) and it is still pulling the left arm. If the left arm is released very efficiently due to the pivot-induced release of PA#4 in a TGM swinging action and the left arm travels faster than the upper torso (which slows down in the later downswing) after the release of PA#4 then a negative torque scenario exists at the level of the left shoulder socket. When one talks about a positive or negative torque happening at the level of the left wrist in the plane of left radial => ulnar deviation when the intact LAFW is parallel to the swingplane or in the plane of left flexion => extension when the release of PA#3 causes the back of the left hand to face the target (which means that the intact LAFW is roughly perpendicular to the swingplane if the golfer has a weak-neutral left hand grip), then a positive left wrist torque scenario exists when the left hand is traveling faster than the clubhead (which has inherent inertia), which means that the left hand is pulling the clubshaft/clubhead - like a toy car being pulled along by a child holding a string in his trailing hand while walking forwards (where positive torque exists if the string is taut). A negative left wrist torque scenario exists at the level of the left wrist when the clubhead is traveling faster than the left hand - like the scenario when the child slows down his walking pace to such a marked degree that it causes the car to travel faster than his trailing hand holding the string (presuming that the car has already acquired enough forward angular momentum to easily overcome any frictional resistance of the wheels against the ground) and under those conditions the string will be lax. If you agree with my description of positive and negative torque, then you should realize why your following statement in a previous post - where you stated "At the start of the downswing and for a short while, the shaft is bent backward and a negative torque is exerted on the wrists by way of arm acceleration" - is nonsensical. In the early downswing, the peripheral clubshaft is bent backwards because the left hand starts to move first due to the release of PA#4 and it is pulling the clubhead (which has inherent inertia) along behind it - so a scenario of positive wrist torque (and not "negative wrist torque") must exist at the level of the left wrist. The statement "negative torque is exerted on the wrists by way of arm acceleration" is nonsensical!
Jeff.
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Post by syllogist on Dec 26, 2019 9:22:03 GMT -5
Dr. Mann,
Please pardon the annoyance.
The reason that I asked the question regarding hand slowing as a sign of negative torque is because the same phenomenon would happen if the shaft were inflexible. It does not matter that the shaft bends forward for there to be a negative torque on the hands (arms, if you will). Shaft bend is a result of centripetal acceleration.
The arms slow during release because the force of the accelerating clubhead is in a direction different than the direction of the arms.
***********************************************************************************************************
Wrist torque (for purposes of example, assume that a club is held):
One can apply positive torque at the wrist joint that seeks to uncock the wrist to release the club. One can apply negative torque at the wrist joint that seeks to prevent uncocking from releasing the club. Both torques at the wrist joint originate from the muscles of the forearm. The wrist can also be passive where one can apply no torque at the wrist joint.
As an example of a passive wrist joint, take the case of a golfer who, at the end of the backswing, does not fully cock the wrist. At the start of the downswing, the acceleration of the arm will cause the club to "fall behind," rotating in the opposite direction of the accelerating arm, and cause the wrist to fully cock. In this case, a force is exerted (not applied) at the wrist joint in a negative direction. This same force at the wrist joint is present in the negative direction even if the wrist were fully cocked. **********************************************************************************************************
Was this helpful in understanding what I was thinking? Let me say that when I write something that is not helpful or just incorrect, I'm in good company.
S
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Post by imperfectgolfer on Dec 26, 2019 10:48:41 GMT -5
Dr. Mann, Please pardon the annoyance. The reason that I asked the question regarding hand slowing as a sign of negative torque is because the same phenomenon would happen if the shaft were inflexible. It does not matter that the shaft bends forward for there to be a negative torque on the hands (arms, if you will). Shaft bend is a result of centripetal acceleration. The arms slow during release because the force of the accelerating clubhead is in a direction different than the direction of the arms. *********************************************************************************************************** Wrist torque (for purposes of example, assume that a club is held): One can apply positive torque at the wrist joint that seeks to uncock the wrist to release the club. One can apply negative torque at the wrist joint that seeks to prevent uncocking from releasing the club. Both torques at the wrist joint originate from the muscles of the forearm. The wrist can also be passive where one can apply no torque at the wrist joint. As an example of a passive wrist joint, take the case of a golfer who, at the end of the backswing, does not fully cock the wrist. At the start of the downswing, the acceleration of the arm will cause the club to "fall behind," rotating in the opposite direction of the accelerating arm, and cause the wrist to fully cock. In this case, a force is exerted (not applied) at the wrist joint in a negative direction. This same force at the wrist joint is present in the negative direction even if the wrist were fully cocked. ********************************************************************************************************** Was this helpful in understanding what I was thinking? Let me say that when I write something that is not helpful or just incorrect, I'm in good company. S I disagree with many of your statements. You stated that "hand slowing is a sign of negative torque". I disagree because I believe that the release of PA#2 happens according to the D'Alembert principle where the clubhead progressively acquires increased angular momentum due to a changing hand arc path. In the early phase of the release of PA#2 the hands are slowing (due to the COAM principle and due to the natural slowing of the release of PA#4) but a positive torque still exists at the level of the left wrist, which means that the clubhead can still gain further increased angular velocity due to the presence of this positive torque. A negative torque scenario will only exist at left wrist level if the clubhead gains so much angular momentum that it causes the peripheral shaft to bend forward. I don't understand how you can conclude that a negative torque scenario exists at left wrist level if there is no evidence of forward bending of the peripheral shaft. Please explain. You also wrote-: "Both torques at the wrist joint originate from the muscles of the forearm." I don't understand why you believe that the forearm muscles produce positive/negative torques at left wrist level in a TGM swinger. I believe that any negative left wrist level torque that may exist in a golfer who uses a float loading technique where the degree of left wrist upcocking temporarily increases between P4 and P4.5 is due the presence of a left hand force that pulls the club handle downwards in the absence of an right-sided hand couple force that prevents the clubhead from falling behind. It does not involve the active contraction of any left forearm muscles. I believe that a positive torque at left wrist level exists between P4 and P5.5 when the left hand pulls the club handle downwards-and-forwards due to the release of PA#4, and that it does not involve an active contraction of left forearm muscles.
You also wrote-: "At the start of the downswing, the acceleration of the arm will cause the club to "fall behind," rotating in the opposite direction of the accelerating arm, and cause the wrist to fully cock. In this case, a force is exerted (not applied) at the wrist joint in a negative direction. This same force at the wrist joint is present in the negative direction even if the wrist were fully cocked." In the rare scenario of float loading where the left wrist upcocks more during the transition to the downswing, then a negative torque must exist at left wrist level. However, that would not produce backward bending of the peripheral clubshaft, which you previously claimed could co-exist with a negative torque phenomenon. I don't understand how you can claim that a negative torque still exists at left wrist level during the P4 => P5 time period if the degree of left wrist cocking does not change. Most pro golfers do not float-load between P4 and P5 and their degree of left wrist upcocking does not change, but their peripheral clubshaft starts to bend backwards between P4 and P5 due to the presence of a positive wrist torque that happens when PA#4 starts to release.
Jeff.
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Post by dubiousgolfer on Dec 26, 2019 11:26:41 GMT -5
Hi S You need to ask yourself what causes the clubshaft to stop rotating in the backswing? The clubshaft has an angular velocity nearing the top of the backswing so what is required to decrease it to zero? The answer is a 'torque'. The next question is in what rotary direction is that torque applied (anti-clockwise = positive, clockwise= negative) ? The answer is anticlockwise = positive (although in physics a positive torque VECTOR is defined in such a way that its direction would point out of the page/screen using the RIGHT HAND RULE) The next question is what part of the golfers anatomy is in contact with the club to apply that positive torque? The answer is the hands. The shaft bend is a 'pointer' to the torque that is being applied by the hands at the grip end and that is the physics of the situation. When you say 'centripetal acceleration' causes shaft bend , it would be better if you could provide a bit more clarity maybe using an example showing the forces in action using a 'free body force' diagram. Trying to explain this in such an abstract way can be very confusing . From what I've read, the forward bend of the shaft going into impact can be caused by an 'Eccentric Loading Force' (ie. a force that is non-aligned through the COM of the club). Therefore the COM of the club will try and align itself with the tail vector of that 'Eccentric Force'. Dave Tutelman examined the research graphs of TruTemper where they used a measuring tool called 'ShaftLab' and found that the forward bend (and clubhead droop) in the shaft was in excess of what was expected (ie. if only the 'Eccentric Force' was the cause of the forward bend). DT's explanation for the excessive forward shaft bend and clubhead droop is below "By the time the clubhead nears impact, it has so much momentum (that's velocity times mass) that the hands can't rotate fast enough to keep up. So the clubhead is pulling the hands through impact, and bending the shaft forward in the process. It may be hard to believe, but most serious swing models show it is true; I investigate this more thoroughly in another article."See link below for that article: www.tutelman.com/golf/swing/handhit.php#shaftbendNote what he says in the summary "We also looked at video frames and ShaftLab traces of PGA Tour pros and Long Drive competitors. They also showed a forward bend, meaning a resisting torque rather than an assisting torque. "
"The reason would appear to be that the grip is rotating too fast approaching impact, due solely to centrifugal acceleration. The golfer's hands cannot move fast enough to catch up to the grip and apply pressure to it."DG
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Post by syllogist on Dec 26, 2019 11:36:07 GMT -5
Dr. Mann,
My statement about the reason why the arms/hands slow during release where the clubhead accelerates in a direction different than the direction of the arms/hands is correct. You can even refer to one of Tutelman's swing physics articles that got it right. He further referred to the different directions as "tension" on the shaft. It is for this reason that there is a partial exchange of energy from arms to club. Just by viewing a double pendulum swinging merely under the force of gravity, one can see the phenomenon at work.
The physics do not change just because one can choose to "float load." This has nothing to do with "swinger" vs. "hitter." Of course there are forces exerted on the wrist joints because of downswing arm acceleration, or because of "hand pull" as you wrote.
As for "swinger" vs. "hitter," my belief is that "swinger" with passive wrists is optimal and that "hitter" introduces forces that negatively affect the rotation and rotational velocity of the club. Interference would be an appropriate word. Thus, I don't bother considering technique or physical forces except in the context of "swinger."
S
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Post by imperfectgolfer on Dec 26, 2019 13:19:26 GMT -5
DG,
I don't understand the "right hand rule" for torque.
Why should there be a torque that is at right-angles to the applied force ("into-or-out of" the blackboard) if the applied force is parallel to the blackboard?
As an example, if an alpha torque is applied at P5 to the left wrist (when the intact LAFW is parallel to the swingplane) then it will cause the left wrist to move in the direction of ulnar deviation, which is parallel to the swingplane. It will surely not be causing a torque that operates in the beta plane that is at right angles to the alpha torque plane (and at right angles relative to the swingplane).
Jeff.
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Post by dubiousgolfer on Dec 26, 2019 18:41:23 GMT -5
DG, I don't understand the "right hand rule" for torque. Why should there be a torque that is at right-angles to the applied force ("into-or-out of" the blackboard) if the applied force is parallel to the blackboard? As an example, if an alpha torque is applied at P5 to the left wrist (when the intact LAFW is parallel to the swingplane) then it will cause the left wrist to move in the direction of ulnar deviation, which is parallel to the swingplane. It will surely not be causing a torque that operates in the beta plane that is at right angles to the alpha torque plane (and at right angles relative to the swingplane). Jeff. Dr Mann (this is complicated to explain and very counterintuitive ) Its a mathematical convention used to represent torque as a vector by assigning a magnitude and direction that points normal to the plane of rotation . This the way mathematicians represent a rotation in vector form so that it can be used in mathematical vector calculus (not just for torque but also other aspects of physics where a rotational quantity needs to be represented in vector form). The right hand rule convention provides a means to decide the direction of the torque vector. You are correct in your example above by saying an alpha torque (when not represented as a vector) is happening physically as described above but the golf scientists have to use vector calculus when they conduct measurements relative to some coordinate frame of reference.Therefore ,those Koike graphs showing 'vector torque magnitudes' in the 'z' direction is really a mathematical graph representation of the 'rotational torque magnitude' in the 'alpha plane'. in a plane that is perpendicular to the instantaneous 'Z' axis directionHope that makes sense. DG PS. On reflection , Koike's graphs become even more complicated to decipher because he is using an 'instantaneous swing plane coordinate frame of reference'. Where the 'z' axis is also changing direction. If my assumptions above are correct , then Graph 'c' becomes almost impossible to use in terms of understanding 'torques' in solely the alpha plane.
Maybe I've got this wrong !!!! Let me check with Dave Tutelman. Addendum 27/12/19After checking Koike's article again , he was using an 'instantaneous swing plane coordinate system' similar to that used by Vaughan 1981 . I first thought that he had somehow fixed the coordinate system to the club because I misinterpreted one of his diagrams. So Dave Tutelman was correct to use Koike graphs to prove negative torque by impact and its actually stated by Koike in the beginning of his research article. "2) the forces exerted by both hands in the axes that are perpendicular to the club shaft show coupled force patterns."
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Post by dubiousgolfer on Dec 26, 2019 19:54:05 GMT -5
Post removed by DG
Removed Post as my assumption about XYZ coordinate system in Koike article incorrect
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Post by imperfectgolfer on Dec 26, 2019 20:51:34 GMT -5
DG,
I do not find your explanations of value because they are vague and unclear and seemingly based on the need to perform certain mathematical calculations - rather than being based on common-sense physical principles.
I think very simply about issues relating to "forces" being applied kinetically during a golf swing action. For example, if an on-plane positive force is applied in the alpha plane at P5, then I cannot perceive that it can produce a positive torque relative to the beta plane or a gamma torque that twists the club around its longitudinal axis. The same applies for a positive beta torque that is applied at P5 - I can understand that it can steepen the clubshaft but I cannot perceive that it will produce another positive torque at right angles to the beta plane and result in an increased degree of left wrist uncocking in the alpha plane if the intact LAFW is parallel to the alpha plane; and I also cannot perceive that it will produce a gamma torque that will cause the clubshaft to twist about its longitudinal axis.
Jeff.
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