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Post by dubiousgolfer on Feb 13, 2023 12:15:39 GMT -5
Dr Mann When that scratch golfer was standing upright and rotating, the pelvis side bend was minimal compared to when he rotated in forward tilt. Let's deduct the effect of pelvis side bend from the ribcage side bend values when approximately 30 degrees, 60 degrees and 90 degrees rotation. 29.68 degrees rotation : pelvis side bend = 3.21 , ribcage side bend = 18.95 : Difference 16 degrees approx 61.17 degrees rotation : pelvis side bend = 8.76 , ribcage side bend = 33.77 : Difference 25 degrees approx 86.68 degrees rotation : pelvis side bend = 13.90, ribcage side bend = 40.90 : Difference 27 degrees approx So if we took into account the effect of pelvic side bend on GEARS measurement of ribcage side bend , there is about 11 degrees increase between 30-90 degrees rotation. If the golfer rotated perfectly with zero pelvic side bend, then I would imagine GEARS would measure ribcage side bend closer to those values 16, 25, 27. Strangely enough , those values are all below the ribcage rotational inclined plane value of 30 degrees (ie. its inclination compared to horizontal). If GEARS measurement of ribcage side-bend misleadingly includes the effect of that 30 degree inclination, then can one assume that the scratch golfer is not doing any ribcage side bend in his backswing?  DG DG |
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Post by imperfectgolfer on Feb 13, 2023 16:18:51 GMT -5
Dr Mann When that scratch golfer was standing upright and rotating, the pelvis side bend was minimal compared to when he rotated in forward tilt. Let's deduct the effect of pelvis side bend from the ribcage side bend values when approximately 30 degrees, 60 degrees and 90 degrees rotation. 29.68 degrees rotation : pelvis side bend = 3.21 , ribcage side bend = 18.95 : Difference 16 degrees approx 61.17 degrees rotation : pelvis side bend = 8.76 , ribcage side bend = 33.77 : Difference 25 degrees approx 86.68 degrees rotation : pelvis side bend = 13.90, ribcage side bend = 40.90 : Difference 27 degrees approx So if we took into account the effect of pelvic side bend on GEARS measurement of ribcage side bend , there is about 11 degrees increase between 30-90 degrees rotation. If the golfer rotated perfectly with zero pelvic side bend, then I would imagine GEARS would measure ribcage side bend closer to those values 16, 25, 27. Strangely enough , those values are all below the ribcage rotational inclined plane value of 30 degrees (ie. its inclination compared to horizontal). If GEARS measurement of ribcage side-bend misleadingly includes the effect of that 30 degree inclination, then can one assume that the scratch golfer is not doing any ribcage side bend in his backswing? DG DG I do not understand why you feel the need to calculate the effect of varying pelvic tilt angles as being relevant in the measurement of rib cage side-bend if he maintains a constant spinal bend inclination angle of ~49 degrees and if he deliberately avoids performing any thoracic spine latriflexion motions during the 90 degrees of clockwise rotation of his upper torso. Jeff. |
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Post by dubiousgolfer on Feb 13, 2023 18:02:48 GMT -5
Dr Mann Can pelvic side bend also affect the angle the spine is tilted? If I flex my left leg and extend my right can it have any involvement in my spine angle tilt? DG PS. Here are the backswing graphs of that scratch golfer and the ones that interested me was the 'Ribcage Side Bend' (red line) and 'Pelvis Side Bend' (green line). Does the 'Pelvis Side Bend' influence the 'Ribcage Side Bend' measurement in GEARS?  |
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Post by imperfectgolfer on Feb 13, 2023 22:41:20 GMT -5
Dr Mann Can pelvic side bend also affect the angle the spine is tilted? If I flex my left leg and extend my right can it have any involvement in my spine angle tilt? DG PS. Here are the backswing graphs of that scratch golfer and the ones that interested me was the 'Ribcage Side Bend' (red line) and 'Pelvis Side Bend' (green line). Does the 'Pelvis Side Bend' influence the 'Ribcage Side Bend' measurement in GEARS? During a backswing action, a skilled golfer can potentially maintain his spinal bend inclination angle unchanged despite the fact that the fact his pelvis is tilting during its clockwise rotation between P1 => P4. What makes that possible is a flexible lumbar spine and its capacity to perform a hula hula motion. Note that hula hula dancers (belly dancers) can rotate their pelvis/lumar spine in small circles without any motion of their upper torso. If a golfer has that same level of hula hula flexibility of the pelvis/lumbar spine unit, then he could maintain a constant spinal bend inclination of his spine during his P1 => P4 time period. Under those circumstances, I do not believe that pelvic tilt (sidebend) values have to be considered when measuring the degree of thoracic spine latriflexion happening between P1 => P4.
What are the yellow and blue graphs?
Jeff.
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Post by dubiousgolfer on Feb 13, 2023 23:28:07 GMT -5
Dr Mann
The yellow graph is just the ribcage swing plane inclination relative to the horizontal (ie. 30 degrees).
The blue graph is just yellow graph value minus the pelvis side bend values (just checking something out for myself but ended up a dead end). It does seem that the ribcage swing plane inclination (ie. 30 degree angle) doesn't have any influence on the GEARS measurement of ribcage side bend. Therefore my assumption on how GEARS might measure ribcage side bend is probably wrong.
DG
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Post by imperfectgolfer on Feb 14, 2023 20:47:19 GMT -5
Michael Neff has produced this video on the topic of ribcage side-bend. I personally find it unhelpful because he has not answered a number of questions that still confuse me. 1) How does he measure ribcage side-bend in terms of which markers are used to make that measurement. 2) Is the measurement of ribcage side-bend measured relative to the ground or relative to the lumbar spine? 3) What is the relationship between a measurement of thoracic spine latriflexion (degree of thoracic spine tilting relative to the lumbar spine) relative to a measurement of ribcage side-bend? 4) He states that Rory McIlroy slightly increases his left ribcage side-bend at the start of the downswing. What is causing that phenomenon? For example, Rory may be increasing his spinal bend inclination angle due to an increased degree of hip joint flexion or he may be increasing his degree of left-lateral latriflexion of his thoracic spine relative to his lumbar spine. Can the ribcage side-bend measurement differentiate between those two very different biomechanical events? 4) In his avatar he shows that the thoracic spine is curving (at the 10:13 minute time point of the video). How does he measure that amount of curvature? Does he have multiple markers placed along the spine to make that assessment? 5) What is the difference between his ribcage side-bend measurement and the measurement of thoracic spine tilt? For example. Milo stated that the GEARS system can measure thoracic spine tilts - although he does not which markers are used to make that measurement.
Milo sent me a short video showing the degree of his rightwards thoracic spine tilt in the early downswing. Here are capture images from that video featuring Milo's P4 => P5.5 downswing action. Note that there are two black boxes containing numbers in each image. Because they are too small to see - note that I have written the numbers below each image. I am not sure of what those numbers represent, but I suspect that they are measurements of the tilt of the lumbar spine (lower number) and thoracic spine (upper number). A negative number reflects a tilt to the left and a positive number reflects a tilt to the right.
If I am correct, then it shows that Milo has 12.6 degrees of leftwards tilt of his thoracic spine and 4 degrees of leftwards tilt of his lumbar spine at P4 (image 1). Image 2 shows the time point when Milo's thoracic spine tilt is zero and that happens well before P4.5 (image 3).
Note that Milo has 13 degrees of rightwards thoracic spinal tilt at P5 (image 4) and 19 degrees at P5.5 (image 5).
Those numbers (if correctly reflective of the side tilts of the thoracic and lumbar spine) obviously do not correlate with the ribcage side-bend numbers at the same P positions. I would like to see Michael Neff explain what is really going on? In particular, I would like to know how many markers are used to generate those GEARS images of Milo and I would like to know where they are placed. Jeff.
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Post by dubiousgolfer on Feb 14, 2023 21:25:36 GMT -5
Dr Mann I think the lower black box number is the pelvic tilt not lumbar spine tilt. I was one of the hundreds of golfers who asked him to explain in detail how GEARS defined and measured ribcage side-bend but he didn't reply back to me (for obvious reasons because was overloaded with similar questions). I think all your questions raise important points and I hope Mr Neff will make another video to provide some more detailed answers (why don't you send him an email). The Thoracic spine tilt angle is explained below on their website: ----------------------------------------- LATERAL TILT (PELVIS, RIBCAGE)  Lateral Tilt is a projection angle on the Y-Z plane (i.e. face on). A projection angle allows you to turn a 3D object into a 2D representation of it. Thus, Lateral Tilt is like the Side Bend metric, but it is a projected angle instead of a global angle. We display values for the lateral tile of the pelvis and the ribcage. ---------------------- I find the above method for measuring lateral tilt of the ribcage and pelvis even more confusing than ribcage side bend. At least we know that both AMM3D and GEARS use the same method to measure ribcage side bend using Dr Phil Cheetham's algorithm. Dr Greg Rose said I was correct in my assumptions on how it was measured and also accepted that the measurements would not be correct if the golfer excessively increased his forward spinal tilt. But when I drew those graphs of the scratch golfer, my assumptions didn't match what I was seeing on those graphs. DG |
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Post by dubiousgolfer on Feb 14, 2023 22:31:16 GMT -5
Dr Mann During my search for more information regarding how AMM3D/GEARS measures ribcage side bend I found something interesting which I never knew. I always thought 'Crunch Factor' was the degree of lateral flexion of the spine but it seems it has its own definition (see further below). I'm wondering if Dr Phil Cheetham and other biomechanical scientists use this definition and measure ribcage side bend with respect to the pelvis -------------------------------- www.ncbi.nlm.nih.gov/pmc/articles/PMC9227529/3.5. Crunch Factor 3.5.1. Rationale The second parameter commonly studied is the crunch factor. It was first introduced by the American Orthopedic Society of Sports Medicine [70]. It was defined as the product of the lateral inclination angle of the torso and the speed of the axial rotation of the torso with respect to the pelvis. The objective of this parameter is to consider both the inclination and axial rotation of the torso that may produce bending stress and shear stress within the intervertebral discs, respectively. These two sources of stress may combine and thus increase stress within the intervertebral disc. The axial rotation speed was considered to determine the loading speed within the vertebrae. Therefore, it attempts to consider their viscoelastic behavior [71] as a combination of axial torque with repetitive flexion/extension motion, which has already been shown to favor hernia occurrence [72]. ----------------------------------------------- DG |
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Post by imperfectgolfer on Feb 14, 2023 22:54:56 GMT -5
DG,
Milo confirmed that the two numbers reflect lumbar spine tilt and thoracic spine tilt, and not pelvic tilt.
I can understand that technical definition of "crunch factor", but I can also understand how many golfers think of the term "crunching-in" as being useful to describe the compression of a soft tissue area of the body eg. right mid-torso during the downswing.
Jeff.
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Post by dubiousgolfer on Feb 15, 2023 9:42:09 GMT -5
Dr Mann Maybe Milo has a new GEARS updated package where they've now got new labels for metrics. Their website might not have been updated and using older definitions. That Golfwrx poster whose company has used the GEARS package for over 3 years said the following: "The three markers on the Gears suit needed to measure this spinal bend are the two on the rear hip bones, and the one at the top center of the spine between the shoulder blades. When at least 3 of the 8 Gears cameras can locate these markers (not a problem), their 3D positions are determined and define the bottom and top of the spine, along with the starting direction of the lumbar spine, which is perpendicular to a line drawn between the two lower markers, since the hip bone is rigid across both sides" If he's correct , then pelvic side bend angle should equal lumbar tilt just like image below. But the fact that they use projected angles makes things even more complicated. ![]()  ![]() You can regard a projection as the shadow of the golfer on a back wall from a face on view. So if the golfer's spine is laterally tilted they would project the spine line on that back wall and measure the angle it makes with a vertical line (drawn on that same wall). You can imagine how flawed that measurement can be if the golfer is rotating while still retaining the same spinal lateral tilt angle. The projected shadow angle would change even though the golfer had not anatomically altered his spinal tilt. Personally, I cannot believe that GEARS designers (including their mathematicians) would not take all of this into account and are probably using more complex equations to arrive at the correct measurements . DG |
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Post by imperfectgolfer on Feb 15, 2023 10:49:36 GMT -5
Dr Mann Maybe Milo has a new GEARS updated package where they've now got new labels for metrics. Their website might not have been updated and using older definitions. That Golfwrx poster whose company has used the GEARS package for over 3 years said the following: "The three markers on the Gears suit needed to measure this spinal bend are the two on the rear hip bones, and the one at the top center of the spine between the shoulder blades. When at least 3 of the 8 Gears cameras can locate these markers (not a problem), their 3D positions are determined and define the bottom and top of the spine, along with the starting direction of the lumbar spine, which is perpendicular to a line drawn between the two lower markers, since the hip bone is rigid across both sides" If he's correct , then pelvic side bend angle should equal lumbar tilt just like image below. But the fact that they use projected angles makes things even more complicated. ![]() ![]() DG If that person is correct about the use of those 3 markers to measure ribcage side-bend, then it obviously cannot distinguish between lumbar spine latriflexion and thoracic spine latriflexion. I also do not know how the GEARS system can accurately measure lumbar spine and thoracic spine tilts using the standard 34 marker system (consisting of only a single spinal marker at T1 and two pelvic markers) if they do not place more spinal markers between T1 and L5, I wonder whether GEARS simply extrapolates and assumes that the lumbar spine must be perpendicular to those two pelvic markers and that their lumbar spine tilt measurement is simply measured relative to a vertical axis that is perpendicular to the ground. GEARS could then extrapolate further and derive a thoracic spine tilt level by comparing the lumbar spine's tilt angle relative to the position of their single spinal marker at T1. If I am correct, then they cannot be accurately measuring spinal tilt angles. Jeff. |
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Post by dubiousgolfer on Feb 15, 2023 10:57:31 GMT -5
We just don't have enough detail from AMM3D or GEARS to even make a judgement about the integrity of their data versus the anatomical reality. I've not yet received a reply to my recent emails to Dr Greg Rose, Dr Phil Cheetham, Dave Tutelman, Dr Kwon and Michael Neff.
DG
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Post by imperfectgolfer on Feb 15, 2023 11:16:20 GMT -5
I still cannot clearly reconcile the GEARS measurements of ribcage side-bend and thoracic spinal tilt. IF GEARS only uses 3 markers (single spinal marker and two pelvic markers) to make these measurements why do they get different results. I have a theory. Consider Milo's driver swing. In image 2, Milo has zero thoracic spinal tilt. How do they get that measurement using only a single spinal marker at T1? First of all, they can get the lumbar spine tilt measurement from the two pelvic markers and get a measurement of -6 degrees. Then, they can derive a thoracic spinal tilt measurement by evaluating the position of that single thoracic spine marker relative to the lumbar spine tilt angle in the coronal plane.
How do they get a left ribcage side-bend measurement at that same P position when the thoracic spinal tilt is zero? I suspect that they make a measurement in the sagittal plane between that single thoracic spine marker and the two pelvic markers. So, if they are really making measurements in the sagittal plane, then their ribcage side-bend measurements will naturally be affected by the degree of rotation of the upper torso. So, in image 2 above they are measuring the degree of forward-directed (sagittal-directed) side-bend of the T1 spinal marker relative to the two pelvic markers and it will generate a finite amount of leftward side-bend.
Jeff.
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Post by dubiousgolfer on Feb 15, 2023 12:34:37 GMT -5
Dr Mann
I think you might be correct because the thoracic spinal tilt due to rotation of the upper torso is now lying in the sagittal plane . The projected angle (see addendum on my previous post under the pelvis image) for position image 2 will therefore be zero. But if the golfer just rotated his torso without any additional ribcage side-bend how do they distinguish between a real anatomical thoracic spinal tilt angle and the GEARS measured ribcage-spine bend angle (in the sagittal plane)?
DG
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Post by imperfectgolfer on Feb 15, 2023 13:06:43 GMT -5
Dr Mann I think you might be correct because the thoracic spinal tilt due to rotation of the upper torso is now lying in the sagittal plane . The projected angle (see addendum on my previous post under the pelvis image) for position image 2 will therefore be zero. But if the golfer just rotated his torso without any additional ribcage side-bend how do they distinguish between a real anatomical thoracic spinal tilt angle and the GEARS measured ribcage-spine bend angle (in the sagittal plane)? DG What is also very strange to me is comparing Rory McIlroy to that model golfer who rotates without any side-bending. Go to the 18:34 minute time point of the AMG video and you will note that they have near-identical spinal bend inclination angle and ribcage side-bend measurements (within ~1 degree) so how can GEARS claim that Rory is actually side-bending his thoracic spine relative to his lumbar spine. Another puzzling fact. The AMG video shows that Rory has a ~40 degrees leftwards ribcage side-bend measurement at P4 and ~21 degrees at P5. However, in his video Michael Neff states (between the 5:48 - 5:58 minute time points of the video) that Rory is roughly maintaining the same degree of left-sided rib cage side-bend between P3 => P5. Jeff. |
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