BM is so desperate to win the argument with Jeffy about the issue of "pelvic deceleration" that he posted this image in his thread.
That image is a TPI graph showing that Rory's pelvis decelerates in the late downswing, then reverses direction after impact and then accelerates again. I suspect that the image was derived from this video.
I will discuss Rory's pelvic motion in depth, but I increasingly believe that any graphical measurement of pelvic rotational speed (like the TPI graph) is meaningless because they measure the movement of the right pelvis, when the critical measurement relates to the left pelvis.
I am interested in optimum golf biomechanics, and I believe that an optimal golf swing involves a "correct" pelvic motion - represented by a "correct" left hip clearing action.
Ben Hogan performs the left hip clearing action perfectly - as demonstrated in this video.
Here are capture images from the video.
perfectgolfswingreview.net/HoganPelvicMotionBackView.jpg [/img]
Image 1 shows Ben Hogan at his end-backswing position. Most of his weight is situated over his braced right leg, and his flexed left leg is relatively less weighted.
Image 2 shows Ben Hogan starting his "left hip clearing action" where he transfers more weight onto an increasingly braced left leg while he simultaneously pulls his left pelvis back in an inside-left direction towards the tush line.
Image 3 shows Ben Hogan at the end of his mid-downswing - note that he has pulled his left buttocks back against the tush line and he is now rotating his left buttocks counterclockwise (in an away-from-the-target direction).
Image 4 shows Ben Hogan nearing impact and image 5 shows Ben Hogan immediately after impact - note how he has established a straightened/braced left leg and note how much he has rotated his left buttocks counterclockwise (in an away-from-the-target direction). By straightening/bracing his left leg, he can rotate his left pelvis fluidly in a non-stop (continuous) manner around his straightened/braced left leg, and that allows him to avoid any further left-lateral sliding of his pelvis towards the target while he simultaneously maintains his speed of pelvic rotation during the late downswing and early followthrough. Ben Hogan's "left hip clearing action" perfectly exemplifies how it is possible for a golfer to avoid pelvic rotary deceleration during the late downswing and early followthrough - while simultaneously preventing the pelvis from sliding too far left-laterally in a targetwards-direction.
The critical factor in a good downswing pelvic motion is the
active factor - the
active movement of the left hip joint as it functions in an optimized "left hip clearing action".
Note that one cannot see the right pelvis in this series of images, and therefore one cannot determine whether the right pelvis is moving forward in the late downswing (between P6 and P7) in the optimum manner. That brings into question - what is the optimum way that the right pelvis should move forward in the late downswing? I think that there is no perfect "gold standard" answer to that question because I think it is biomechanically irrelevant if the right pelvis moves forward in a slower-than-optimum manner - because the right pelvis (right hip joint) is becoming progressively unweighted in the later downswing and it is being
passively pulled forwards. Because the movement of the right pelvis is passive, many inertial factors could delay its forward momentum in the late downswing eg. a lack of right hip joint flexibility, keeping the right heel down, not allowing the right knee to move appropriately outward, putting 10 golf balls in one's right front trouser pocket thereby increasing the weight of the right lower body. The TPI measurements (and presumably the MATT measurements) are probably measuring the motion of the right pelvis by placing markers on the right side of the pelvis, and I therefore find their graphical measurements non-useful. I am interested in perceiving if a golfer moves his left pelvis in the optimum manner during the downswing (using Hogan's left hip clearing action) and I know of no reason why the left hip joint's rotational motion has to decelerate in the late downswing (just prior to impact).
Does Rory have the optimal left hip clearing action and does he decelerate the left hip joint in his late downswing (as implied by the TPI graph)? The answer is no! I think that Rory does
not decelerate his left pelvis during his left hip clearing action.
Here are capture images from the Sports Science video.
perfectgolfswingreview.net/McIlroyPelvicMotion.jpg [/img]
The TPI researcher created this model which accurately depicts Rory's pelvic motion during the downswing.
Image 1 shows Rory at the P5 position. He has rotated his pelvis counterclockwise and his pelvis is minimally open to the ball-target line (rather than being square) and this is a testament to his very fast pelvic rotary motion in his early downswing that creates a lot of torso-pelvic separation (like Bubba Watson).
Image 2 shows him at the P5.5 position, image 3 shows him at the P6 position and image 4 shows him at impact. Note how open his pelvis progressively becomes during the later downswing and there is
no evidence of any deceleration of his left hip joint motion during his left hip clearing action. Any measurement of pre-impact pelvic deceleration (as seen in the TPI graph) doesn't reflect a slowing of his left hip clearing action, which is perfectly well executed.
Image 5 shows that Rory's pelvis temporarily reverses direction immediately after impact. Why does it occur?
Here is a capture image showing the TPI graph.
I have placed a blue arrow to direct your attention to the dipping of the red graph that happens post-impact - and that reflects Rory's pelvic reversal phenomenon. Greg Rose implies that it is due to his external/internal abdominal oblique muscles pulling his pelvis backwards. That explanation makes no sense to me!
I think that a more rational biomechanical explanation relates to the fact that the upper torso starts rotating very fast at that early followthrough time period - see the spike in the green graph. If the upper torso rotates very fast through impact, it will produce a counterforce that will decelerate the pelvis in the early followthrough - see the Cheetham video explanation in post #22.
What is interesting is that the pelvic reversal phenomenon only involves the right hip joint (which is unweighted and essentially floating freely in space), and not the left hip joint (which is solidly grounded because Rory is rotating around his straightening/braced left leg during his left hip clearing action). The fact that the right hip joint temporarily reverses direction in the early followthrough, before being passively pulled forward again in the later followthrough, is biomechanically immaterial because the movement of the right pelvis is passive and functionally irrelevant.
This debate between jeffy and BM about any pelvic deceleration happening in the later downswing is meaningless because they are not discussing i) what they mean by pelvic deceleration and ii) what effect any pelvic deceleration will have on a golfer's ability to execute a well-executed golf swing. BM desperately wants to prove that the pelvis decelerates in the later downswing, but he has never provided a cogent argument (based on sound golf swing biomechanics) that explains why he thinks that pelvic deceleration is important. I am still waiting for that explanation.
Jeff.