Golf, Ground Force, COP and COM

This information is a little more technical than what I normally write about. However, I feel that this is an important topic which is getting misconstrued by golfers, and the media. In this article, you will learn;

• What is the difference between pressure and weight?
• Why that is important?
• Some practical information for players

A special thank you to Dr Sasho Mackenzie for reading through and verifying the info in this. Also, to Dr Mike Duffey and Dr Kwon for information I have picked up from them via online forum topics.

It would be wise of me to mention that, when dealing with pupils directly, I use drills which simplify all of this information and allows them to develop better motions with minimal thought processes.

 

Pressure Info

With the rise of technology on the lesson tee, we now have the ability to measure things we can’t see. Trackman has brought about a revolution in our ability to measure the most important elements to a desired shot (namely impact variables), and we can now even measure the forces that we produce with the ground.

Companies such as BodiTrak, Swingcatalyst and SAM offer products which allow us to measure things such as the shift in pressure, and some of the units even measure the amount of ground force and 3D force vectors. Many teachers are now using these devices in lessons, so it would help if pupils could grasp a better understanding of some of the basic elements.

 

What is Ground Force?

When we are standing still, we exert a force on the ground which we call our weight. If you weigh 200 lb, you will be exerting 200 lb of downward force, and the ground will exert an equal and opposite amount of force back on you.

If you were to push into the ground with enough force, this would accelerate your body upwards -which is essentially what happens when we jump. This will become important later.

 

Pressure is not Weight

The biggest misunderstanding I see often is the false idea that pressure and weight are the same.

Not only are pressure and weight different, they can often be completely opposing

What do I mean by this?

Imagine I am standing motionless – my centre of pressure (or COP) would be balanced between the middle of my feet.

If I were to just lift my left foot up off the ground, my body would be exerting more force under the right foot (100% of my pressure), and so we would say that my COP (centre of pressure) has shifted towards my right foot.

 

The important thing to understand here is that, even though my centre of pressure moved 100% backwards, my centre of mass (body) stayed roughly in the same place laterally.

 

COP and COM

What happens if you keep your centre of mass (body) in the same place but lift your front foot off the ground? That’s right, you fall to the left.

So, we see here that centre of pressure and centre of mass can be completely opposing. In essence, by lifting my left foot off the ground, my

• COP has moved 100% to the right foot,
• but my COM has started to move to the left.

Lifting your left foot off the ground is not the only way to move pressure back – you could also push harder into the ground with the right leg, or you could physically move the mass over to the right side.

 

In the first picture, I have moved my mass to the back foot and pressure has also moved right. In the second picture, my mass is moving forwards, but my pressure has moved 100% to the back foot (I know this because I am doing a stepping drill and my front foot is actually off the ground). In the third picture, I have pushed harder into the ground with my right leg, thus moving my pressure to the back foot.

 

Heel/Toe

The same is true of centre of pressure in the feet with relation to mass.

Often, on pressure mats, we will see the pressure of a player move to the left toe area – especially during transition. While this is an important feature of good players (it creates dynamic stability, helps resist the forces the club produces on the golfer and helps the rotation of the body), many people see pressure moving forwards as a bad thing. Again, this is usually a misunderstanding of the relationship between mass and pressure.

As a quick test – stand up. Get into a nice balanced position, then (without moving your mass), pick your heels up off the ground. In doing this, your Centre of pressure essentially moves to your toes – but what happens to your body? It moves BACKWARDS

By picking up your heels, your centre of pressure will move forwards and your mass will fall backwards.

Why is this important? Well, I have seen many players working on keeping their pressure away from their toes on the false misunderstanding that they are falling forwards (towards the ball to target line). The reality is, this may be the worst thing this player can do, as, without that toe-biased centre of pressure movement in transition, you could not only dramatically reduce power and rotational forces, but you may also inhibit dynamic balance.

 

More than One Way

Which one of these swings has more pressure on the left side?

 

You will be surprised to hear that, actually, my driver swing (the one on the left) not only has a greater percentage of pressure under the front foot, but has a higher magnitude of force also.

Don’t forget, mass is not pressure.

In my driver swing, I made a more concerted effort to press into the ground. Not only this, but I also have my right foot off the ground at impact – so I know that 100% of my pressure is forwards. In the swing on the right, I not only have my back foot on the ground, but I am making an effort to push with it. This is not to say that these swings are effective, it just shows the disparity between mass and pressure.

Understand that, although it is important to get the pressure forwards in the downswing, you can do so with many different body positions. A driver may need a different body position than an iron. For example, typically (I have had this measured), my swings with irons and driver have around 80-85% of pressure on the front foot at impact. However, my mass is more behind the ball with a driver than it is with an iron – allowing me to make the low point of my swing farther back, increasing my angle of attack with the driver (allowing me to hit the ball higher and farther).

For these reasons, looking at pressure traces alone can be misleading. Ideally, they should be integrated with some video analysis or 3D motion capture.

 

Turn Up the Pressure

A recent study of baseballers showed that peak ground reaction forces were associated with higher velocities. In golf, the same is true, with an increased ground force producing the potential for more speed (there are other factors too). This is because creating higher ground reaction forces (in conjunction with other elements) offers us the ability to create more rotational speed with our body segments.

Baseballers and golfers produce more pressure under their lead foot than 100% of their weight. In other words, if a golfer weighs 200 lb, they may produce more than 300 lb of force under their lead foot during transition.

“How can you produce more pressure than you weigh” I hear you say? Well, imagine standing on an old analogue weighing scale and jumping on it. You may weigh X amount, but for a brief moment, you will make the needle jump much higher.

Long drive champion showing 210% bodyweight pressure under her lead foot. Pressure can = big power

 

Left Arm Parallel

Some important elements to a good golf swing come between the phases where the left arm is parallel in the backswing, to the same position in the downswing. This is where we can create some good ground forces.

 

Between left arm parallel in backswing and downswing

During these points in the swing, we should actually start the act of changing direction. The timing of this can vary for players with different swing lengths, but as a very general rule, this point in the swing (pre-transition) is where you want to see the mass of a player start to move forwards (to the front side). Many players leave this move until too late in the swing, reducing their ability to create power and get to their left side.

We see Tiger here shifts a lot of his body mass towards the left side between the backswing left arm parallel (left pic) and downswing left arm parallel (right pic). You will also notice with a lot of good players that they also drop in height by this point in the swing – especially with irons. We can see this clearly in Tiger’s swing above.

McIlroy is one of the longest hitters pound for pound – watch how his head drops during transition.

Again, we see quite a dramatic shift forwards while the body has dropped in height between these two phases.

This should feel like the pressure under the lead foot is lifting pre transition (you don’t actually have to physically lift the heel), and that you are ‘falling’ into the left side, ready for phase 2.

 

Lead arm parallel in downswing

During this point in the swing, the vast majority of tour players will see a peak in the total force under the lead foot. This is because they are starting to reverse the forwards movement of their body and create rotation.

By left arm parallel with the ground, most tour players have already moved forwards enough, and are now starting to move away from the target.

Players who didn’t move left enough during transition will have problems here, and they usually end up continuing to slide through impact, which is less than optimal (reduces the player’s ability to provide speed to the club), or they end up being so far behind the ball that their low point is unplayable (lots of fats and thins).

By this ‘left arm parallel’ position, players are applying a lot of ground force under the lead foot – similar to stamping on a weighing scale to make the needle jump. This ground force is magnified by

• The lifting of the pressure and ‘falling’ into the left side during transition
• Shear forces which helped accelerate the player’s mass forwards
• The subsequent re-planting of the lead foot
• The left leg attempting to straighten

During this time, players are often applying so much force into the ground, that (later in the swing, usually around impact) it can manifest itself in a jump. That’s why so many long hitters have a jump through impact. Bubba Watson even gets airborne at impact.

If you look at swings on the long drive circuit (the real big bombers who can hit over 400 yards), they often exhibit these moves in more dramatic fashion.

 

Down and Forwards, Up and Away

Essentially, the moves of great players often have 2 phases

• PHASE 1 – Moving down and forwards until left arm reaches parallel
• PHASE 2 – Pushing up and away from the ball and target from left arm parallel until impact

Here we see a clear down and forwards move (phase 1) from Tiger. Rory also exhibits this move greatly, as do many top players.

Then we have the back and up motion from left arm parallel in downswing until impact (phase 2). This can often be seen in professionals where it manifests itself in motion, such as Tiger and Rory.

Here we see Tiger with a head which is higher than post-transition, and also farther back.

We see a lot of backwards motion (not so much upward motion) with Nicklaus here

Long Drive champion Jason Zuback exhibiting the push away from the target.

Here’s Spieth showing a down and forward phase 1

Followed by an ‘up and back’ phase 2

Here’s Mcilroy showing a down and forward phase 1

Followed by an up phase 2

Also, this fits in nicely with an article I wrote on parametric acceleration.

Not all ground forces are created in the same way.

• Some players (such as Sadlowski and Nicklaus) raise their head in the backswing, drop it back to where it was in phase 1, then back up and away in phase 2
• Some players (Tiger, Mcilroy, Spieth) maintain or drop their head height in the backswing and phase 1, before pushing up and away into a position which is still lower than where they were at address (in other words, they are closer to the ball).
• Other players may drop their height during transition (phase 1), yet their head height maintains relatively steady throughout the strike. It’s not that they aren’t trying to push up and away in phase 2, it’s just that the fact their body was accelerating towards the ground (during transition) and the pull of the club through impact means that it is a game of tug of war. It might look like a ‘steady head’, but there is a battle of pulling going on.
• Players can also exhibit different patterns with driver vs irons, due to different goals at impact.

 

Side Note

It is important to mention that the above information pertains mainly to speed generation. However, some of these moves not only create increased speed, but they also help with consistency and low point position. An argument could be made that some of the movements presented here may not be optimal for ultimate control of the golf ball.

However, I will leave it to you to decide on the truth of that. While I am sure there may be a point of diminishing returns with regards using head/body movement to create ground forces, the fact that Spieth, Tiger, Mcilroy, Nicklaus etc all had significant and very defined body/head movement patterns may show otherwise.

 

Technical Work 

This type of information would be classed as technical work, as, if you were to implement this information, you are dealing directly the movement patterns.

If you are to do this, I would suggest periodizing this work to the off-season, when results don’t matter as much. This is because, in my experience, while implementing some of these ideas may offer some long term benefits, thinking about the body movement while playing is often not the most optimal of thought processes.

If you want to learn more about this, The Strike Plan shows you more about the technique described here, as well as skill drills to use on the range/at home/on the course to improve your strike quality. Learn more by clicking the image link below

 

Cliff Notes

• Pressure is not weight/mass – in fact, the two can (and often are) completely opposing i.e. pressure goes back, weight goes forwards.
• There is more than one way to get your pressure forwards. Different clubs may require a forwards pressure but different body positions
• Professionals and long drive champions create massive amounts of pressure under their lead foot – far exceeding their bodyweight
• This is usually created by a drop in led foot pressure during the transition, followed by an aggressive replanting of the pressure in the downswing
• This pressure usually peaks by around left arm parallel in the downswing
• Long hitters can create so much ground pressure that it manifests itself in a jump around impact.
• Two phases in the swing are a down and forwards part (phase 1) followed by an up and back part
• Through impact, it is a game of tug of war with forces pulling the golfer down toward the ball to target line. Even if the player is producing the phase 2 forces, it may not always manifest itself in the body moving up through impact (it depends on who wins the game of tug of war.