WEBVTT

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In this video we're going to break down the center of mass versus center of

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pressure discussion. So there's there's a really hot topic in golf right now if

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you haven't heard of it it's it's looking at ground force reaction and

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specifically looking at center of mass versus center of pressure. So I'll give

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you a couple ways that you can kind of visualize it and how you can understand

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how it applies to your swing. I've got a couple different yardage sticks I'm

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going to use as different kind of reference guides. So we'll start with

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just the two stick model. So we'll call the orange this is going to be where my

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center of mass is. So that's roughly gonna be around where the middle of my

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body is. So if I if I was to go like this the middle of my body is kind of

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somewhere out here. It's not truly where my belly button is. It's if you take

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all

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the mass of my body and you kind of average it out. Now the yellow stick this

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is going to be more my pressure. So right now it's balanced between my two

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feet. I can shift all my weight here or all my pressure over here or I could

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shift all my pressure over here and for a split second I could have my mass

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still here and my pressure there by picking out my foot. So these two

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different objects are going to help us create moment arms and torques. Now

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these

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are some fancy words for the forces that I'm creating either against the

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ground or up against the club. Now and we should we should quickly break down

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kind of why we want these longer moment arms. When it comes to how I'm

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applying force against the ground the magnitude so how much I'm pushing the

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direction and the how long or the the impulse which is the force times time

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all are going to factor into this equation. So what happens is if I have

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my mass right on top of my pressure kind of like this it's very hard for me to

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create any type of lateral force. It's essentially and the reason is these two

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are right on top of each other so I basically have what's called no moment

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arm. There's no distance between these two. To understand that moment arm

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concept

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I always use the example of opening a door right. So we'll imagine that I've

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got a door right here and here's here's my hinge right is right over on this

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side. So they would put the door knob over here where I would turn it and then

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a

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small amount of force over here is going to move at a time. Now they could have

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put the door knob right next to the hinge but if I if I apply that same

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amount of force it barely moves it compared to that same amount of force

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down here. And the reason is because of the distance away from this axis of

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rotation it's going to increase well the basically the formula is the force

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times that distance. So the greater the distance the less force I actually have

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to apply to get a big force. So if these two are right on top of each other I

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can't anything where I try to push in one way or the other is going to be all

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muscular I'm not going to have any of this kind of mechanical advantage. So the

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the times in the golf swing where this ground force reaction stuff is really

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important is going to be the early stages of transition or from the top of

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the swing until about delivery position. And the the neat thing is it's going

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to

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shift. It's going to go from one side where I'm kind of building to another

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side once I start bracing that I better have some distance between these two to

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allow me to capitalize on this little kind of door example. So before we jump

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into the specifics of how it applies to the swing I always like to run through

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kind of how you can look at ground reaction force in general. So for example

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if I was to jump I'm gonna push against the ground now if I had a little thing

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reading how much I'm pushing it against the ground what you would see is as I

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lower myself down I actually unweight slightly so you would see the pressure

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as I'm going down I'm actually not pushing against the ground very hard

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that'll help eccentrically load my muscles so then I can spring up so I

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accelerate against the ground and that causes me to go up. I push against the

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ground the force coming back from the ground allows me to take that force

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transmit it through my body and create it into upward motion. Now if we looked

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at kind of lateral movement or horizontal movement if I want to walk

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forward I'm going to push against the ground that way so I'm going to push

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against the ground that's going to cause me to go forward. Now if I'm standing

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like this where my mass is pretty much on top of my pressure I'm going to

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slightly move my mass forward and that allows me to not have to push as hard

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to go forward. If I was running or what you'll see sprinters do in the

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starter blocks is they'll get their their mass as far forward as they can so

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now two things I'm pushing more horizontally and any amount that I push

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is going to transmit immediately into forward motion because I have this huge

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moment art. The one caveat is the same reason why we as golfers wear spikes and

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why sprinters wear cleats as well is I need friction because if I start pushing

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too hard and the ground is not pushing back hard enough my foot's going to slip

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and it's not actually going to create motion. So there we've got the easy ones

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which is up and down side to side then you've also got rotation. Rotation is a

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little bit trickier because basically you're going to look at wherever the the

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object is in order to create rotation I want to push perpendicular to that

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axis of rotation. Right so if I were to push this way I'm not going to get

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nearly as much rotation out of it as if I pushed 90 degrees to wherever that

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center is. So what ends up happening in the golf swing is in order to create

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rotation I'm going to push that foot back that way and I'm going to push that

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foot that way and those two are going to create this rotation or spiral

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mechanic. Now what I frequently see is more people do this where they push this

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too much that way and then this one is going to tend to be more like that and

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so they don't get quite as much rotation as they could if they were to optimize

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it. So that's why in the early extension section we talk a lot about the push

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the ground away from you that's really to get this model of kind of pushing

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more

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in this back 30 back 45 instead of all the way back behind me. Okay so it's a

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rough breakdown as far as how the feet interact with the ground. Now we have to

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explore a little bit this how do I control my mass compared to this pressure.

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So when I make a backswing part of the reason that we want to be somewhat

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centered is so that my mass is here my pressure is here that allows me to push

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against the ground and kind of create this rotational speed. One of the other

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things is the more that I stand up right that actually tends to bring these two

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together the the further that I drop down I should say so I'll exaggerate it

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right if I was to drop down a lot now my mass pushing through the foot is going

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to be like this if I was standing up it's pushing like that so I'm not going to

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get as much horizontal movement. The easy way to illustrate that is if I was

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looking at I was used to like to watch Barry Sanders change direction he was a

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famous football player and he would get really low to the ground so because he

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would be low to the ground he could have his mass he could have a huge moment

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arm between where his pressure was with his cleat and where his mass was where

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someone who was a little bit taller trying to change direction they wouldn't

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be able to apply nearly as much force. So in golf by keeping this centered

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pivot

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in the backswing now I can push from this pressure over here on the right to

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start moving the mass to the left. Now my mass doesn't move as fast as the

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pressure does I'm going to shift my lower body but my upper body stays a

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little bit more centered so the pressure goes from pushing here to pushing here

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to help me now start that bracing process. The tricky thing is all of that's

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going

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to happen between there so I go from pushing to pushing kind of as I go step

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step. Now part of the reason why you'll see a lot of golfers lower during those

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pushing phases you know someone like Tiger someone like Rory you'll see them

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drop down in order to create more friction against the ground so that they

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can apply more of these shear and rotational torques or twist their feet

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against the ground. So that's a lot of kind of complicated phrasing and

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science to understand how the body is working with the ground. Now here's the

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one caveat I've talked with a number of other kind of applied golf sport

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science guys and my personal opinion is that good ground reaction force is more

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of a sign that you're doing a lot of things right than something that you can

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ultimately train. It's kind of like if I had you squatting and I and I put you

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on a force plate and I put some weight on your back and had you squat down and

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I

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said okay that was good but really good squatters are going to squat more than

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that or so why don't we just put more weight on you. You might look at me like

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I'm crazy but that's essentially when you tell someone hey you know push a lot

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harder against the ground. It could be that the arms in the club are out of

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position and so they can't push harder at the ground you kind of have to clean

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that up stuff that stuff up first. Similarly if I cleaned up you know your

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knee tracking your core activation your shoulder and scapular stability then

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we can safely add more weight and we can get you to push against the ground

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harder in that squat metaphor. So if you get on a reading and you see that

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you've got some force or some pressure or weight distribution issues I would

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always look at the face-to-path relationship first make sure that that

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is relatively solid before you're going to be able to really maximize any of

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this ground stuff. So that's always my take I know that there are guys that go

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to the ground first but my personal preference I've had more success cleaning

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up the face-and-path and then creating the speed with the body or then

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addressing how to create speed with the body rather than vice versa because it

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's

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very hard to create more speed and better force and pressure against the

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ground whether it's in the creating speed or the bracing to transmit speed it's

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very hard to add speed if you know that that's going to make you contact the

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ball worse. So hopefully that helps you visualize helps you understand if you

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have a little bit more of a centered pivot on both sides if your body lowers

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slightly especially during transition if you then when you start pushing

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through

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that lead foot if that creates a little bit of this lift back move both of

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those

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are going to be the big times where especially in this frontal plane we're

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going to be able to maximize these center mass center of pressure relationships

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and that's ultimately gonna help give you the most efficient way to create

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speed in the handle and as long as you can direct that to the golf ball it'll

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help you hit the ball far and straight. So with a club you can see that I'm

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pushing through with that right foot and then I'm pushing through with that

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left

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foot. Now the important thing is not just how much I push that's why I started

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this by saying there's those three important factors how long I push and

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the direction that I push are just as important as how much I push and I tend

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to find that most people struggle with the direction or how long. So from a

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practical application I'll tend to say hey that was good just I want you to

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feel

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like you push a little bit longer or hey that wasn't too bad except you push

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more that way I want to push a little bit more that way that will help kind of

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create some of this side bend movement and then when I add that front foot that

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will really help create some of this side bend movement. So don't get caught up

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on how much I think that's the last one that you can really start trying to

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amplify but worry about how long and what direction for the most part most of

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the pushing is going to be done by kind of right about in here whatever I've

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done

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at that point actually it's probably even a little bit higher but whatever

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I've done at that point my next goal is just to take advantage of that and

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transmit as much as I can to the club what we teach in the stocks full swing

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will give you some of the best mass versus pressure versus ground force

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relationships and ultimately that's how we're able to build some of this

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consistency into this complicated thing we call the golf swing. Also from a

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practical standpoint I tend to think that the more important one is not so

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much how well I push with that trail leg but more so how well do I keep this

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relationship in the frontal plane and be able to push with that lead leg. So if

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I get totally on top of the golf ball like this then when I push it's gonna

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have a hard time creating side bend out of it that's gonna make it hard for me

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to have a real shallow angle of attack especially with the longer clubs so if

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you're focusing on kind of that feeling of pushing through the ground I would

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focus on that one there which is the bracing of that lead leg to help trigger

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the whole release. Looks something like that.