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Post by tomdavis76 on Jan 16, 2013 21:36:47 GMT -5
And just think if no one questioned anything, if the case was truly closed, then Jacobs and Finney would be telling students or peers two different stories.In the end I think this is a good exaple why people should question statements and not just accept everything as a fact. I think the Mike Jacobs mea culpa is very interesting and revealing. This reference frame confusion didn't happen by accident: Jacobs was taught in educational courses that different reference frames were used and states that this revelation is news to "a lot of folks". hmmmm.... What the hell else have "a lot of folks" been "taught" that's wrong??
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Post by imperfectgolfer on Jan 16, 2013 21:52:32 GMT -5
I have read a lot of Cheetham's papers in the last 2 days and I now believe that there is no such thing as "global reference measurements". That term simply applies to their measurement device which is placed directly behind the golfer. That device allows all the data points from the sensors to be interpreted by a computer so that they can determine where the axis of rotation is at every moment in the downswing for different body segments, and they can then determine the rotational velocity of each body segment (eg. pelvis and thorax) around the local axis for that body segment. I therefore believe that MJ's claims about two reference measurements were wrong. However, I am not interested in MJ's wrong opinions - I am interested in the reality of a golfer's body motion, and I would like to know whether a golfer (like JS) is really decelerating his pelvic rotational motion in his downswing action - as implied by TPI's pelvic rotational velocity graph presented in their kinematic sequence graphs of JS's swing?
Jeff.
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Post by gmbtempe on Jan 16, 2013 22:29:29 GMT -5
I see it the same way Jeff, whether there was mistakes made along the way I am looking for the end result.
It is surprising though that Jacobs uses such a expensive and comprehensive tool yet there was a major difference in what he was taught and what the system actual does.
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Post by imperfectgolfer on Jan 17, 2013 0:13:41 GMT -5
Greg,
We seemingly see things the same way. I have no personal stake in this conflict between Jeffy and BM/BM groupies. I am mainly interested in knowing whether a 3-D device can help me better understand golf swing mechanics/biomechanics, and so far I have never learned anything useful from 3-D graphs. I will simply wait to see BM's promised video on 3-D devices to see if he can say anything useful about 3-D measurements. I have certainly never learned anything useful from Tapio's posts regarding 3-D measurements.
Jeff.
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Post by imperfectgolfer on Jan 21, 2013 18:06:02 GMT -5
Jeffy posted a back view video of Sadlowski's driver swing in his forum See post #58 in this thread - jeffygolf.com/showthread.php?518-Jamie-Sadlowski-s-hip-rotation-into-impact/page4Here are capture images. He then stated-: " Here's an interesting view of Jamie because it gives you a good look at the "push/pull" rotation around the spine: left leg extension that "pulls" the left hip joint away from the target, and right leg extension that pushes the right hip joint towards the target. When do the legs STOP firing? At "hips square", when "massive pelvic deceleration" allegedly starts??? That looks like where the legs START to fire!" I disagree. I think that the legs do not fire, especially not the right leg. I think that pelvic rotation is not secondary to a "leg firing" action, and I believe that the legs move passively in response to motion of the hip joints. I think that JS pulls his left hip joint back to the tush line at the start of the downswing, and that "left hip clearing" action causes the pelvis to rotate. I believe that maximum pelvic rotation speed occurs at P5 - when the pelvis become square to the ball-target line. I dont think that JS "fires" his right leg between P5 and P7. I think that the right leg straightens passively when the right hip joint moves away from the right foot as the pelvis rotates to a ~50 degrees open position by impact. Jeff.
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Post by tomdavis76 on Jan 21, 2013 19:32:43 GMT -5
What can power Jamie's hip joints other than the legs?
Also, "passive" legs might be a plausible theory if his swingspeed were 95mph, but it's 140 or so...
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Post by imperfectgolfer on Jan 21, 2013 20:05:37 GMT -5
Jeffy,
You are free to believe that JS is thrusting his right pelvis forward between P5 and P7 due to an active right leg extension maneuver. However, I cannot fathom what purpose that would serve. I believe that the pelvis only needs to become 30-50 degrees open at impact for the upper torso to be able to rotate efficiently in the mid-late downswing and through impact. I don't believe that a golfer will necessarily benefit by an active right leg extension in the late downswing if he uses a CF-arm release action - like JS. Finally, you have provided no evidence that the pelvis is accelerating between P5 and P7. In fact, the TPI graph shows pelvic deceleration (from ~ 600 degrees/second => ~ 300 degrees/second) during that time period, and you have never provided any evidence to disprove that finding.
Jeff.
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Post by tomdavis76 on Jan 21, 2013 20:30:35 GMT -5
Jeffy, You are free to believe that JS is thrusting his right pelvis forward between P5 and P7 due to an active right leg extension maneuver. However, I cannot fathom what purpose that would serve. I believe that the pelvis only needs to become 30-50 degrees open at impact for the upper torso to be able to rotate efficiently in the mid-late downswing and through impact. I don't believe that a golfer will necessarily benefit by an active right leg extension in the late downswing if he uses a CF-arm release action - like JS. Finally, you have provided no evidence that the pelvis is accelerating between P5 and P7. In fact, the TPI graph shows pelvic deceleration (from ~ 600 degrees/second => ~ 300 degrees/second) during that time period, and you have never provided any evidence to disprove that finding. Jeff. First, deceleration does not mean torque isn't being applied at a constant or increasing rate. As the arms and club extend, the body's MOI increases, which acts as a brake. Second, I have seen Rick Malm's analysis and it is far more convincing to me than AMM3D. Third, the Motion Reality data I analyzed does not show the rapid drop-off of AMM3D, and it is based on more sensors. Fourth, the left leg thrust may be more important than the right leg; 4Dswing analyses I have seen suggest that is the case.
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Post by imperfectgolfer on Jan 21, 2013 20:46:02 GMT -5
Jeffy , you wrote-:
"First, deceleration does not mean torque isn't being applied at a constant or increasing rate. As the arms and club extend, the body's MOI increases, which acts as a brake."
It is irrelevant if constant/increasing torque is being applied to the pelvis if that torque doesn't actually accelerate the pelvis between P5 and P7, and there is no "evidence" that pelvic acceleration is happening. I don't think that arm/club extension represents a major factor that would decelerate the pelvic rotation, although I do believe that the increasing speed of upper torso rotation will brake the pelvis (as Cheetham has explained).
You also wrote-: "Third, the Motion Reality data I analyzed does not show the rapid drop-off of AMM3D, and it is based on more sensors.
I don't understand this claim. You posted a comparison between your pelvic angle measurement (based on the Motion Reality data) and the TPI pelvic angle measurements, and you implied that they were basically equivalent. Are you now revising that claim?
Also, why should more pelvic sensors increase accuracy of measurement? Are you claiming that TPI's pelvic angle measurements are inaccurate?
Jeff.
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Post by tomdavis76 on Jan 21, 2013 22:19:24 GMT -5
Jeffy , you wrote-: " First, deceleration does not mean torque isn't being applied at a constant or increasing rate. As the arms and club extend, the body's MOI increases, which acts as a brake." It is irrelevant if constant/increasing torque is being applied to the pelvis if that torque doesn't actually accelerate the pelvis between P5 and P7, and there is no "evidence" that pelvic acceleration is happening. I don't think that arm/club extension represents a major factor that would decelerate the pelvic rotation, although I do believe that the increasing speed of upper torso rotation will brake the pelvis (as Cheetham has explained). You need to brush up on your physiscs... Of course. I made that claim before I differentiated and graphed the AMM3D positional data. Haven't you looked at the two graphs of rotational velocity? That can't be a serious question... interesting phrasing...the measurements may be accurate for what the sensor is actually measuring, whatever that is, but I don't believe the AMM3D pelvic rotational velocity data is an accurate representation of hip rotation in Jamie's swing. I believe Rick Malm's is.
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Post by imperfectgolfer on Jan 21, 2013 22:23:38 GMT -5
Jeffy wrote-: "Fourth, the left leg thrust may be more important than the right leg; 4Dswing analyses I have seen suggest that is the case."
I would not dispute that claim. If you look at what happens to JS's left leg in that two-photo sequence (previously posted) one can see that his left leg straightens between P5 and P7 and his left thigh simultaneously rotates counterclockwise, and he also develops a positive pelvic O factor and an open pelvis by impact. Those biomechanical events allow his right shoulder to move downplane when his upper torso rotates around his rightwards-tilted spine (which has also acquired some lateral bend and an increased amount of secondary axis tilt during this time period) and that allows his right forearm to paddlewheel efficiently into impact in the late downswing during the right arm straightening action.
In other words, I believe in the biomechanical logic of these causally-interrelated biomechancial events, but I don't think that they depend on the presence of pelvic acceleration between P5 and P7.
Jeff.
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Post by imperfectgolfer on Jan 21, 2013 22:32:47 GMT -5
Jeffy wrote-: "interesting phrasing...the measurements may be accurate for what the sensor is actually measuring, whatever that is, but I don't believe the AMM3D pelvic rotational velocity data is an accurate representation of hip rotation in Jamie's swing. I believe Rick Malm's is."
That's why I don't believe in any of the measurements made by 3-D researchers, and/or Rick's/Jeffy's measurements. Jeffy also continues to simply believe whatever he wants to believe!
I much prefer looking at KM's superb Phantom camera slow-motion videos, where I can clearly see what is happening without having to deal with biased measurements/claims made by different researchers.
Jeff.
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