Ground Reaction Forces In Golf
Ground reaction forces have become a hot topic in the world of golf over the past couple of years. For a long time people have understood that the swing starts from the ground up and how you are using the ground can have a significant impact on the speed you are able to produce as well as your ball striking quality. Ground reaction forces are noticeable among the best players in the world such as Justin Thomas (video below). You can see the feet actually leaving the ground because of the amount of force they are applying in the swing. This is interesting, but how can this apply to the average golfer and should you even try to do something like this? Keep reading to learn more about the importance of ground reaction forces and how we can measure them as well as a few examples of my experience with the Swing Catalyst Force Plates and how it can benefit you.
What are ground reaction forces?
First off lets establish what are ground reaction forces? The laws of motion dictate that for every action there is an equal and opposite reaction. During the golf swing, a force is exerted on the ground by the golfer. In response, the ground exerts a force of the same magnitude in the opposite direction on the golfer. These forces are then transferred through the lower body to the core, then the arms to the club and finally the ball at impact. This is something every golfer does in some capacity.
When most people think about ground reaction forces they think of the vertical force as demonstrated by Justin Thomas in the video above. While this is important there are actually 3 forces that occur in the swing:
Horizontal Force: This is your right/left force. This would be the forces towards and away from the target.
Torque/Rotational Force: This is the forwards and backwards force coming from the feet. There is an opposite force forwards and backwards that occurs in each foot which helps to create rotation throughout the body. You can see a good visual of this in the video below of the hockey player swinging a golf club. If you remove the friction from the ground you can see these opposite forces created by each foot.
3. Vertical Force: This is the up and downward force. As the golfer pushes down into the ground the ground pushes back creating an upwards force. Golfers such as Lexi Thompson, Justin Thomas and most of the professional long drivers are great examples of golfers who produce a lot of vertical force. In cases such as this the feet may even come off of the ground.
How can you measure Ground Reaction Forces?
Thanks to advancements with force plates we can actually analyze these forces throughout the swing and use this data to improve your swing and club head speed. Ground reaction forces are not something that can be analyzed with traditional video analysis or pressure mats such as BodiTrak. The picture below is of my ground reaction forces. The three graphs on the right side of the picture (purple, yellow and blue) correlate to each of the forces mentioned above: horizontal, torque/rotational and vertical. In the next several sections we will discuss some of the important aspects of this data.
How Much Force Do You Produce?
The first thing we can learn from these graphs is how much force you produce from the ground. In the picture with the graphs you can see the peak of each graph. In each of these graphs you can also see a black bar. This indicates the PGA average for each of the forces. Basically this lets you know if the force you are producing in each area is a lot or a little. Take a look at a few examples below to see how these forces can vary amongst golfers.
The first example is of my ground reaction forces. If you look at this picture you can see my horizontal forces (purple graph) are within the PGA tour range. My torque/rotational graph is below the PGA average and my vertical forces are above the PGA range at 220% of bodyweight. The vertical forces are my strongest power source.
In contrast, look at these graphs from a different golfer. You can notice that the purple graph is at or slightly above the PGA average. The torque/rotational graph (yellow) is below the PGA average and the vertical force (blue line) is almost non existent. The main takeaway is to appreciate some of the unique differences in how golfers use the ground. At the moment we won't discuss what is good and what is bad. It can be easy to assume that more force is always better. However, this is not always the case and I will discuss this in a later section.
What is the sequencing of your forces?
Most golfers are somewhat familiar with the kinematic swing sequence of the golf swing. The swing starts from the ground, then the lower body fires, followed by the torso, the arms and finally the club. There is also a sequence that should occur among your ground reaction forces. Amongst the best golfers in the world the order of which these ground reaction forces peak is nearly identical. The horizontal force should occur first, followed by the torque/rotational force and finally the vertical force.
What is the timing of your forces?
When you apply these forces in the swing is equally important as to how much force you apply. The ground forces you create ultimately need to be transferred throughout the body and to the club at impact. In many instances these forces are peaking way too late in the swing. In some cases I have seen the forces peaking at impact or even after impact.
When I had my swing analyzed on force plates I was guilty of this as well. For example my normal 7 iron speed is 98 mph. Initially my vertical force peaked right at impact. With a few modifications in set up I was able to get my vertical forces to peak earlier and had an immediate increase in club head speed to 103 mph. The interesting point was that I felt I was swinging with the same effort and intensity level.
So when should these forces occur? The horizontal forces should happen around the top of the backswing. The torque/rotational force should occur around lead arm parallel and the vertical force should occur around club parallel.
Is more force always better?
In the above sections I shared a lot of data and graphs. This insight is great and all, but how can you actually apply this information to improve your ground reaction forces? There can be a couple of ways. One is to make adjustments to your setup position in your swing. Using myself as an example I was creating force too late in the swing. In order to get the forces to occur earlier it was arecommended that I square my lead foot instead of flaring it. In addition I changed my pressure shift from 95% in my trail side to 80%. This combination helped result in the forces occurring at the proper time . itor such as Trackman can help to make sure any changes in ground forces are also translating to good contact and ball striking. Being able to adjust the ground forces also relates to the next topic, the body.
What is the relationship between your body and your ground reaction forces?
As I mentioned above the goal is to tune/modify the ground forces to the unique needs of the individual golfer. As each golfer has a unique body and a unique swing, it would make sense that their optimal ground forces may differ as well. I will use my experience on force plates as an example of this. In my case which I highlighted earlier in the article, I produced very high vertical forces with my lead leg. I also produced very high horizontal (side to side) force with my trail leg. With some physical testing it was determined that my left leg was also my dominant leg at creating force. However, my initial swing didn't match up with this. I was shifting a lot of weight to my trail side in the backswing and having a hard time getting back to my lead side in time which resulted in the ground forces being produced way too late. I was not using my greatest strength/source of power. With a few adjustments to better match my body and swing I was able to get these forces occurring much earlier and experienced a significant jump in speed. This is just one example, however, I have seen a variety of cases where this varies from golfer to golfer.
How can you improve your ground reaction forces?
In the above sections I shared a lot of data and graphs. This insight is great and all, but how can you actually apply this information to improve your ground reaction forces? There can be a couple of ways. One is to make adjustments to your setup position in your swing. Using myself as an example I was creating force too late in the swing. In order to get the forces to occur earlier it was recommended that I square my lead foot instead of flaring it. In addition I changed my pressure shift from 95% in my trail side to 80%. This combination helped result in the forces occurring at the proper time and a spike in speed.
Another aspect to this could be improving your body and addressing physical limitations that could be limiting force production. Also if you want to create larger forces, you need to have a body capable of handling those forces. The forces created from the ground need to ultimately be transferred through the body and if there is a weak link in the body these forces will either dissipate by the time they get to the club or could also lead to an injury if the body isn't capable of handling it.
Below are a couple additional resources to learn more about force plates and ground reaction forces. The first is a podcast link with Dr. Scott Lynn and Michael Dutro talking about everything related to ground reaction forces and force plates. The bottom video is a summary of one of my lessons on the force plates. If you go to the Measured Golf Youtube page you can watch several other lesson summaries with this technology.