Pelvis Motion in Elite Players

[iacas]

A week or so ago, a known pot-stirrer who rarely (never?) offers anything of his own kicked up another storm on some instructor Facebook groups.

He had problems with the photo in this article: https://www.golfdigest.com/story/swing-by-numbers-new-study-unlocks-6-swing-secrets. Specifically with this image:

The pot-stirrer's issue is that the image looks a little too much like S&T.

The data from GolfTec shows that the average Pro's "pelvis"* moves 3.9" toward the target on the backswing, while the average amateur's moves "only" 2.55" (toward, also).

The paragraph accompanying the picture makes it clear that the "hips" or "pelvis" are measured at the tailbone, which even if it rotated 45° while the center of the hips remained in place, would move about 2.8" (assuming the tailbone is about 4" from the center of the pelvis). Measuring the hip sway at the tailbone is a pretty bad way to go about it, I agree, because again rotation alone will result in "sway" toward the target even if the center of the hips is actually swaying the other direction, away from the target.

But regardless, GolfTec's data said that the tailbone moved 3.9" toward the target in good players, and 2.55" in amateurs. It showed a strong correlation to ability, and ~1.4" is reasonably significant.

But pot-stirrer had a problem with the actual PHOTO.

Does the blue guy look a little left? Well, his torso is tilted away from the target. So I like that. But his right leg is close to "locked out straight" (then again, so is Red Guy's). That doesn't look like 1.35" difference, either.

Perhaps it would have been better had GolfTec simply shown the hips of the golfers and shown their starting position and a little dot on the tailbone where the thing is actually measured.

Better yet, GolfTec could put an additional sensor on the front of the golfer's hips, by his belt buckle, to measure the center of the pelvis a bit more so (this may require an adjustment for a very fat person).

Anyway, pot-stirrer's issue was with the picture. Not the actual data. Several commenters said the 3.9" was misleading, but it was made pretty clear in the article that the measurement is from the tailbone, so even if the sensor is 4" from the center of the hips, and the hips rotate 45°, that's 2.8" of movement right there.

But… let's look at what the hips actually do during the golf swing. Here's a tweet with some basic information.

A larger version of that image is here:

Not that it matters, but here are what the terms are.

01 BA = Breakaway (when the clubhead moves off the ball)
02 MB = Mid-Backswing
03 LB = Late Backswing
04 LBA = Late Backswing Arms
05 EPR = End of Pelvis Rotation
06 TB = Top of Backswing
07 EDA = End of Delivery (Arms, ~A5)
08 ED = Early Delivery (roughly A6)
09 MD = Mid-Delivery (roughly A6.5)
10 BI = Ball Impact
11 MF = Mid-Followthrough

Forward/Backward (thrust) is relative to the ball: closer to the ball or away from the ball.
Toward/Away (sway) is relative to the target: toward or away from the target.
Upward/Downward (lift) is vertically.

The middle line is the mean (average), and the lines on each side of the graph are one standard deviation away.

Some data points in mean (EPR) format for the green values, in centimeters (cm), are:

EPR: 1.2 (2.7)
TB: 3.0 (2.9)
EDA: 6.8 (2.9)

Between BA and MB (points 1 and 2), the pelvis can be seen swaying backward slightly. How slightly? If EPR (5) is 1.2 cm, then the max sway back away from the target is about 1.6cm. As 2.54cm = 1 inch, 1.6cm is about 0.6".

This very small sway back is used by some to "kick start" the forward motion: at EPR (5), it's 1.2cm forward, at TB (6, A4) it's 3.0 (or 1.2"). From 7 to 10 (impact), the mean is about 7.4cm @ 7/EDA, 8.4cm @ 8/ED, 10cm at 9/MD, and 10.95cm at 10/BI/A7 (impact).

So… the hips move back about half an inch in these elite players hitting driver, before they pivot and sway slightly forward during the backswing. During the downswing, BAM, the pelvis slides to about 11cm forward of their starting location: almost 4.5".

Again…

And…

BTW, these numbers are pretty darn close to what we wrote in the 5SK Instructor training manual back in 2012 or so.

[Pablo68]

I find the stuff fascinating and the numbers don't lie.

[RandallT]

I was a little surprised how the hips move forward toward the ball. Up/down made sense. To/from target, check.  But my gut on the Forward/backward measurement was that it would’ve been more constant than it is.  

I’m not trying to debate the info. Just wanted to ‘fess up on an inaccurate mental image of what was going on, in case others had a similar sense.

 

[billchao]

46 minutes ago, RandallT said:

I was a little surprised how the hips move forward toward the ball. Up/down made sense. To/from target, check.  But my gut on the Forward/backward measurement was that it would’ve been more constant than it is.  

I’m not trying to debate the info. Just wanted to ‘fess up on an inaccurate mental image of what was going on, in case others had a similar sense.

 

The average is less than an inch by impact. I'd call that "steady" 

[Typhoon92]

This picture IS misleading.  I remember reading the article, seeing the picture and wondering Wtf...

If u look at the graph background and draw a line up from the lead foot on the blue you see that he's in the right position.  Blue guy stays over the ball.  The difference between the 2 is so great I think that's where it throws people.

Maybe putting an address position in there would have helped.

Edited January 6, 2018 by Typhoon92

[RandallT]

2 hours ago, billchao said:

The average is less than an inch by impact. I'd call that "steady" 

Glad to know the pros aren’t goat humping then 

[JonMA1]

Maybe I'm misunderstanding the OP, but the illustration does make it look like his lead leg is stiff. It's likely traced from a photo and as such accurate, but it fails do a good job of indicating the lead leg/knee is bent forward.

Again, sorry if I'm misunderstanding the post.

 

Edited January 7, 2018 by JonMA1

[iacas]

3 minutes ago, JonMA1 said:

Maybe I'm misunderstanding the OP, but the illustration does make it look like his lead leg is stiff. It's likely traced from a photo and as such accurate, but it fails do a good job of indicating the lead leg/knee is bent forward.

I don't think it does that at all. It's an illustration. They can't add a crap ton of lines and stuff.

And I don't think the lead knee is what anyone had an issue with. It's not what the sensor is measuring, or what the discussion was about.

The focus was on the pelvis and hips.

[JonMA1]

31 minutes ago, iacas said:

And I don't think the lead knee is what anyone had an issue with. It's not what the sensor is measuring, or what the discussion was about.

The focus was on the pelvis and hips.

So the "pot stirrer" thought the position of the pelvis and hips in the illustration looked like "Stack & Tilt"? Because almost every PGA image I could find shows those closer to the target at the top. Same with the angles of the back and trail leg.

I guess I'm confused as to why anyone would think that was different or wrong. Doesn't really matter I suppose.

[iacas]

2 hours ago, JonMA1 said:

So the "pot stirrer" thought the position of the pelvis and hips in the illustration looked like "Stack & Tilt"?

Basically.

2 hours ago, JonMA1 said:

I guess I'm confused as to why anyone would think that was different or wrong. Doesn't really matter I suppose.

It doesn't really matter, right. It's an illustration. The OP was operating under the guise that Nick Clearwater is turning GolfTec into a fully S&T type swing. Which the OP hates.

[Xerex]

The image is misleading.  The sensor is on the tailbone so unseen in the graphic.  I saw Clearwater demonstrating  the data on Golf Channel this morning and went to the practice range with it. Transformed my impact in minutes after years of struggling with divot after ball for years.  I'm not complaining.

Edited January 19, 2018 by Xerex

[lastings]

anyways, regardless of what the picture looks like...   

Since reading this post a few days ago, this thought has really helped out.   I've working hard to make a full shoulder turn to help get my hands deep.  Focusing on making a good turn of the hips has really made it easier and even more natural to get my shoulders turned. 

note: I think that trying to open up my hips right away has forced me to pull the club back on an inside path, but I can fix that by focusing on keeping my lead shoulder down, i think.   

 lots of swing thoughts going on right now...    That's what winter is for, i guess. 

 

[Lihu]

On 12/19/2017 at 6:43 PM, iacas said:

The paragraph accompanying the picture makes it clear that the "hips" or "pelvis" are measured at the tailbone, which even if it rotated 45° while the center of the hips remained in place, would move about 2.8" (assuming the tailbone is about 4" from the center of the pelvis). Measuring the hip sway at the tailbone is a pretty bad way to go about it, I agree, because again rotation alone will result in "sway" toward the target even if the center of the hips is actually swaying the other direction, away from the target.

I can only draw one conclusion from this diagram, better golfers have bigger butts. The "pot stirrer" objected to that, obviously. 

[Mr. Desmond]

Went to youtube and looked at Nick Clearwater from August 2016 .. go to the :54 second mark

 

 

 

Edited January 24, 2018 by Mr. Desmond

[Xerex]

Anyone who plays golf is looking for a silver bullet solution. For me at least this is one of those. It corrects a number of different positions in the back swing which in turn give consistency of ball impact on release. Elegant, simple and most of all repeatable. 

[Groucho Valentine]

Add this to the list of things about golf i probably didn't need to know....