Daniel Gray is a PGA professional and a Senior Instructor at the Sea Island Golf Performance Center in Sea Island, GA. We were able to join Daniel while he was working with LPGA and Ladies European Tour player Katie Burnett. Katie and Daniel were focusing on her ground mechanics using BodiTrak, specifically working on timing of her transition. We asked Daniel to break down Katie’s center of pressure and vertical force data on BodiTrak and share how he worked with her to improve her transition.
The conversation of foot and ground pressure has been very helpful for many athletes and players across many sports for a reason, it’s an athletic sensation and natural approach to creating speed. As an instructor I hear most players talk about the sensations of pressure as if it is second nature. We are all pressure experts, as we are all using pressure constantly throughout the day to walk around and stay balanced. Athletes are very familiar with these pressures and sensations, where the issue is the timing and magnitude of these pressures when maximizing speed in a golf swing.
LPGA Tour player Katie Burnett is a great example of how to use the ground and measuring the magnitude of pressure relative to your body weight can have some significant effects on club kinetics and ball flight. Looking at the timing and magnitude of Katie’s pressure we can make some strong assumptions about how she is using the ground differently to create different club kinetics. Here were her Trackman numbers before discussing the correct sensation on how to use the ground and the timing of that transition.
With this new BodiTrak software and mat, instructors can start to get an idea of vertical pressure magnitude relative to a player’s body weight and in addition to horizontal timing of pressure (represented by center of pressure). By measuring the total force of the player (“body weight unit”) at address, BodiTrak is able to measure how much pressure a player is applying to the ground relative to their body weight. The number 1 represents the total body force of the player, so anything below 1 the player is creating less than that force and anything above the 1 the player is creating pressure that would be in addition to that baseline.
Notice in the first image below where Katie is in her setup position and the orange, yellow, and blue lines are all matched with the baseline of 1, which is equal to her body weight. During the take away the total pressure drops below the baseline of 1. This is due to the pressure shifting away from the ball (to the trail leg) and the unweighting of the lead leg, thus there is less total pressure applied to the ground. This process is critical for reloading of the lead foot in transition to encourage a functional kinematic sequence. The setup and take away are very similar during the before and after images, so notice below how the setup and takeaway start. Notice that the total pressure drops below the 1 in the early takeaway and mid backswing in the below image (far right).
If you will take a close look at the before image (below, left) where Katie is at the top of her backswing and about to start her transition into the downswing, you should notice that her trail foot pressure is significantly higher than her lead foot pressure in the before image (the yellow line is higher than the blue line). In the after image (below, right) you can see that this has been altered and the lead foot vertical pressure equals the trail foot and pressure is changing to the lead foot earlier than before. The horizontal shift of the pressure back to the lead side earlier is what is causing this addition of vertical pressure in the lead foot. If players get their pressure stuck back on their trail foot for too long during the transition they will not be able to apply the downward pressure into the ground and use the rebound pressure that helps create functional sequencing.
Typically players will reach this position after the unweighting process in the downswing, when maximizing their clubhead speeds and sequencing. Notice the drop in total pressure was larger on the after image below, there is a larger troth just before this image. This allows for more use of the ground vertically in this position of the downswing.
When the shaft reaches this vertical position in the downswing most elite players are starting to push up from the ground at a higher rate. Notice the lead foot pressure went from .40 to .70, so you could say this is a 75% increase in pressure in the lead foot. This allows Katie to add speed to the lower body longer during the downswing and this is what helps the pelvic motion continue to rotate longer in the downswing.
You will see players reach their highest vertical peak between club parallel and impact. You can see her total vertical pressure just before impact reaches 1.25 on the before image. The player’s body weight times this number could give you an idea of how many pounds of pressure a student is applying to the ground. In Katie’s “before” swing, her highest vertical pressure is 1.25 with a clubhead speed of 92.4, angle of attack -2.2, and a low point that is 2.6 after the ball before discussing direction of pressure and timing. This creates a launch angle of 9.2, a total height of only 53 feet, and total carry of 198.1. Note: If some of you readers are wondering the smash factor on this shot it was 1.51. The lowest smash factor measured of the 20 tee shots she hit was 1.49, twice. Center face contact, all day.
Now, if you look at the After image you can see that she was able to reach up to 1.7 times her body weight just before impact after focusing on the importance of timing and direction of pressure through impact. This max vertical pressure is helping the clubs angular speed, which has the highest correlation of clubhead speed according Dr. Young-Hoo Kwon, biomechanics professor at Texas Women’s University.
After getting Katie to create more efficient timing in the horizontal pressure, we then talked with Katie about how the direction the vertical pressure should be applied. She has some pretty good changes for 20 swings.
The horizontal pressure shift conversation was that the pressure needed to reach her front foot as she was finishing the top of her backswing or just before transition. This would allow her to create more vertical pressure, earlier in her downswing. We then discussed the importance of direction of pressure, this is a more specific conversation and players need to feel that they are pushing with their lead foot in a direction of away from the target (back) and away from the target line (left for a right handed player). This would create a direction of force that looks like the following image.
These are charts from Dr. Young-Hoo Kwon’s research at Texas Women’s University just north of Dallas, where he
preforms research on high level tour players and collegiate players. This is a glimpse at what a researcher would use to understand a player’s efficiency and speed. Notice the similarities in the Combined GRF chart and the BodiTrak combined vertical force chart. The direction of force helps the player rotate their pelvic and thus create higher speeds with all parts of the body and club.
This was a very simple, none technical conversation with Katie and her response was “this allows be to be athletic in my swing” and we never once talked about a chart. Understanding the reasons for speed and how to create more speed can help simplify your instruction and your game as a player, if you have an educated instructor that can relay on these simple concepts of speed generation and pressure.