# Pelvis Rotational Acceleration

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Yesterday I came across in reading a scientific article entitled: Comparison of Kinematic Sequence Parameters between Amateur and Professional Golfers.
Essentially, the authors have evaluated differences (in terms of average and dispersion) between the kinematic sequence of pros and amateurs and presented several interesting values table; I'll try to exemplify and summarize the article to get to my point as quick as possible (in case you might read the article attached).
Among others, they measure the rotational acceleration values of the main segments:

Because the body consists of linked segments (pelvis, thorax, Arm, club, etc.), the amount of force in the impulse applied by the distal segment (ClubHead) is essentially the sum of the force from all the joints used (muscles in each part actively contribute to the swing).

This means that, if the pros accelerate (rotate) the pelvis less than 2.1 (kd/s2) then the resulting thorax acceleration would be inferior to 3.3. Note that thorax acceleration gain 57% (3.3 / 2.1 = 1.57) respect to pelvis due to the friction between the two sections.
Note also that the "progression of the gains" for the pros is pretty similar to the amateur's:

Amateurs rotate (accelerate) the thorax 53% more respect to the pelvis (+57% for the pro, not such a difference in terms of acceleration), the lead arm 43% more respect to the thorax (here the pros transmit a few more rotation, +55%) and the club 82% more respect to the arm (pros 73% more, pretty near values).
The big difference that stands out to me is the starting values of these progressions: pelvis acceleration for the amateurs is only 1.5 compared with 2.1 that pros swing with (about 30% less!).
Due to higher pelvis torque (hence higher rotational acceleration), pros reach higher CH speed (assuming all remaining factors being equal). This result matches with the idea of swinging from ground up during the DS.

Maybe we amateurs focus too much on arms and upper body when we aim to speed?!
Well, I think I'll start rotating my pelvis damn fast from today... at least I'll try my best to , and you?

titlest ComparisonofKinematicSequenceParametersbetweenAmateurandProfessionalGolfers (speed in the pelvis).pdf

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Great topic. Thanks for posting. Here's a related post from @iacas from 2016:

At the end of that post, he and Dave try to get power from just using arms, and they get approximately 70% of club speed that way.

And here's another related idea on the stalling of the hips:

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13 hours ago, Gaetano Fasano said:

Maybe we amateurs focus too much on arms and upper body when we aim to speed?!
Well, I think I'll start rotating my pelvis damn fast from today... at least I'll try my best to , and you?

Interesting info. Thanks for sharing.

Some amateurs may benefit from focusing more on lower body. But not everybody has the same mental models for technique or 'grooved feels'. Some people get their lower body to 'react' to intended or actual movement of the upper body.

Case in point, an infielder in baseball steps and clears their hips when they make more than a 'toss' throw. Some might consciously step, some might not. I doubt any of them other than a raw beginner would consciously think about their hips vs. their arms or the target. But they still clear them.

Edited by natureboy

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5 hours ago, natureboy said:

Interesting info. Thanks for sharing.

Some amateurs may benefit from focusing more on lower body. But not everybody has the same mental models for technique or 'grooved feels'. Some people get their lower body to 'react' to intended or actual movement of the upper body.

Case in point, an infielder in baseball steps and clears their hips when they make more than a 'toss' throw. Some might consciously step, some might not. I doubt any of them other than a raw beginner would consciously think about their hips vs. their arms or the target. But they still clear them.

That's really interesting . . .I would definitely belong to the group of people who's lower body 'reacts' to the intention of my upper body.  More and more I'm seeing my golf swing as an arm/hand movement . .and everything my body does is to support/enhance this arm/hand movement.

If I were going to take a bowling ball and toss it, underhanded, up on the roof, for example . .my thoughts and intentions would be on my arms and hands . .and not at all on my legs . or the squat action . . .which, of course, would be heavily involved in me getting the ball on the roof.

edit:

This is a really interesting topic, in general.  I'm starting to think, for myself only, that this kind of information . .while really interesting . .is totally secondary to mental pictures and intention..ie . .the actual data about the positions a golfer achieves are not complete without the context of those positions . .ie . .the mental picture.  The golfer is not stalling his hips just for the sake of stalling his hips.

Edited by Rainmaker

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21 hours ago, Gaetano Fasano said:

This

21 hours ago, Gaetano Fasano said:

Maybe we amateurs focus too much on arms and upper body when we aim to speed?!

And @RandallT said: At the end of that post (Reply to Power Sources in Golf), he (@iacas) and Dave try to get power from just using arms, and they get approximately 70% of club speed that way.

Definitely.

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Hi guys and thanks for posting!

I agree that focusing on the upper body may result more natural, let me say easier, making the timing less complicated. If you hit the sweet spot doing so, you'll be longer and straighter than making a faster swing hitting on the toe/heel. I know that there are pros which actually focus more the upper body and I understand that may be kind of people who comply better with such a style of swing.

But maybe, rooting to a proper use of the lower body (gradually, working at the DR), "spinning" more the hips in the DS, should lead to higher rotational speed of the core. This is just my interpretation of the data in the article since, on average, most of the pros rotate the hips 30% more than us.

When I focus on my arms/torso in the swing, I feel that my pelvis assists the upper body in the rotation naturally but some how passively. It's like missing some part of the potential propulsion which can derive from our powerful legs muscles. From a very extreme point of view, a passive lover body might also be seen as a ballast that slows down the development of torsion.

Even if I understand the weight shift analogy, the comparison with the baseball player seems not to be the more appropriate in this case because in the golf swing we don't lift the lead leg to load in torsion and, more in general, we make a much more composed movement. I always felt naturally comparing my right side bending in the DS with bowling ball release posture but that balls are so heavy that I can't really manage comparing the leg action we are used to implement in golf. For this post, I would see more adequate thinking to hogan's "skipping the stone" and the "two-handed basketball pass" drills (and he was very good with his lover body ).

My thought is not "can we swing better spinning the pelvis?" but more something like "may our CH get faster if we spin harder our pelvis?"; above data seem to confirm the latter.

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What I see from that… amateurs swing more slowly.

That's about all that I can really conclude. They don't rotate their pelvis as fast… because they can't.

Just a first glance, but I've seen things like this before. Since the ratios are almost all still the same, amateurs are sequencing things about the same (kinda), but they're just slower at every stage.

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9 hours ago, Hatchman said:

And @RandallT said: At the end of that post (Reply to Power Sources in Golf), he (@iacas) and Dave try to get power from just using arms, and they get approximately 70% of club speed that way.

Definitely.

I went to that thread due to @RandallT's post. I added a post to that thread. I agree with the basic premise that 'arm swing' is a big source of energy. However, arm muscles (other than from trail arm extension) may not contribute as much as people might assume from the thread title. You can clearly see that Dave's shoulders & upper thoracic / torso move at least a few degrees rotationally. If you pinned his shoulders so they couldn't move, I'm sure there would be significantly less power. Swinging the arms witht that kind of restriction would still involve more 'shoulder' muscles than arm muscles.

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6 hours ago, iacas said:

They don't rotate their pelvis as fast… because they can't.

Hello iacas, thanks for your comment and many compliments for the TST, great site.

They can't because of phisical limitations? Or it's a matter of focus on wrong parts of the body during the swing? Or it just happens after a certain time?

I just noticed something probably obvious and maybe already well known: more pelvis spinning imples more CH speed. But that's very interesting to me since, in case it's true, I might work on that very specific aspect to improve my performances.

For example, should we work more on pelvis muscles improvement (like in a jim) than others aspect to increase CH speed?

Thank you again and best regards.

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On 1/18/2017 at 3:00 PM, natureboy said:

I went to that thread due to @RandallT's post. I added a post to that thread. I agree with the basic premise that 'arm swing' is a big source of energy. However, arm muscles (other than from trail arm extension) may not contribute as much as people might assume from the thread title. You can clearly see that Dave's shoulders & upper thoracic / torso move at least a few degrees rotationally. If you pinned his shoulders so they couldn't move, I'm sure there would be significantly less power. Swinging the arms witht that kind of restriction would still involve more 'shoulder' muscles than arm muscles.

The point of that thread is to limit what the lower body contributes, particularly via vertical GRF.

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10 hours ago, iacas said:

The point of that thread is to limit what the lower body contributes, particularly via vertical GRF.

I understood. I saw potential for 'arm swing' to be misconstrued by some as 'arm effort' (which I don't think was being advocated) without some extra clarification / caveats for the terminology used.

@Gaetano Fasano here's an interesting perspective about 'arm focus' vs. 'hip focus'.

The ugly suckers below (cortical homunculi) represent how the body is mapped in the brain (proportion of cortical area devoted to the nerves in the body part). Notice how 'hands heavy' the representation is. It's possible the spinal cord and ganglia devote extra 'area' to lower body movements relative to the hands, but the implication is that it's less 'consciously' controlled or influenced motor patterns and possibly best driven by intentions focused on 'educated' hands.

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@natureboy thank you very much for your last comment. It was really informative to me. I do want to relay more on my hands.

After reading RandallT's suggested post and looking at the video on the driver from a chair, I remembered a video with Monte (link below) which is a bit long but treats about the "arms driven" swing concept (hope I can say like this).

I remember that when I tried to just deliver my hands to the follow though position from the top of the backswing, a fast as possible, without thinking about my pelvis, I got great contact and more distance. I didn't realise the whole picture that time cause I was wondering about my left wrist flipping, avoiding fat the ball, etc. and I was more of the idea that rotating faster (specilly with the left hips and left shoulder) would had induced a flat left wrist at impact.

I now think that pelvis rotational improvement may derive from faster arms movements. This weekend I'll try that at range to see if my hands shall gain more shaft leaning this way (with an hands & arm swing).

Sorry for going a bit OT talking about my swing.

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