How To Analyze A Pressure Trace With Dr. Sasho MacKenzie

 

Dr. Sasho MacKenzie is a professor in the department of Human Kinetics at St. Francis Xavier University and one of the leading researchers in golf biomechanics.  Sasho is also one of our lead advisors at BodiTrak and a lead instructor in our Golf Ground Mechanics course and upcoming Sports Medicine Certification.

Cordie Walker of Golf Science Lab was with us during filming for Golf Ground Mechanics at Mark Blackburn’s facility at the Greystone Country Club in Birmingham, AL.  While there, he asked Sasho to take a look at his swing on BodiTrak.  They filmed the analysis, which we thought was very worthy of sharing.  If you’ve never used force and pressure (or if you just want to see how one of the foremost authorities on ground mechanics analyzes data), this article should be a good place to start.

 

ADDRESS & TAKEAWAY (0:40)

The first thing that you’ll notice about Cordie is that he has a prominent trail leg bias at address, with almost 70% of his pressure in his right heel.  Though Cordie may have assumed

Just before the club begins to move back, you’ll see the CoP move slightly to his lead side. This “lead leg press” is a common move as golfers push off the lead leg to move their body mass and club away from the target to start their backswing. 

 

BACKSWING 

As Cordie approaches the top of the swing, he has over 90% of his pressure on his trail side, mostly concentrated under his heel.  This is a pretty elite position, especially considering that Cordie doesn’t have much sway [if you want to see a great example of this on TOUR, check out TPI’s Dave Phillips analysis of Jason Day]. From here Cordie can push off into his lead side and generate plenty of speed.  We’ve often used an analogy of a sprinter in starting blocks: A sprinter must pushes into starting blocks to send their center of mass in an opposite direction. 

 

TRANSITION

1:11 Another hallmark that we see in above-average ball strikers is that pressure begins to move towards the lead side prior to the finish of the backswing.  This is a common misconception with many beginners who believe that they should remain loaded into the trail side until they start the downswing.  This often results in inefficient kinematic sequences, with the torso leading the hips in the downswing.  Pressure to the lead side is vital, and one of the fastest ‘fixes’ you can make for club golfers.

 

DOWNSWING

Pay attention to the CoP trace here in Cordie’s downswing.  It is representative of a key concept that must be understood by every instructor or golfer using force and pressure. As he approaches shaft vertical downswing [a key position we covered here], you’ll notice that Cordie’s CoP appears to be “moving towards” his lead toe. In fact, at this point over 90% of the pressure in his lead foot is in the toe and less than 10% in the heel.

To the uninitiated, it may appear as of Cordie is preparing to early extend, a swing characteristic defined by excessive thrusting of hips towards the ball in the downswing. If the trace represented Center of Mass (weight) that might be the case. However, we are measuring Center of Pressure, and in this case, the opposite is true. The concentration of pressure in the lead toe is representative of how hard Cordie is pushing with his left leg to 1) manage the momentum of the club on the downswing and 2) clear his hips, allowing him to achieve his desired out-to-in clubpath and play a fade.

 

Understanding the difference between weight and pressure is an absolute prerequisite for using a tool like BodiTrak.   We think pushing through the lead leg in the downswing is an excellent representation of how golfers can move their Center of Pressure and Center of Mass in opposite directions.  Look at Jason Day’s trace here.  If you didn’t match it up to video, you could conclude that he was early extending when, in reality, that is not the case.

 

IMPACT (2:15)

At impact, you’ll see the center of pressure big to move back toward the lead side.  It’s not a key element of Cordie’s swing (the ball is gone, after all), but it illustrates how CoP can be influenced in a number of different ways.  In the golf swing, Center of Pressure generally moves for three different reasons: 1) we are lifting a foot; 2) we are pushing harder into the ground with a foot and 3) we are pushing or lifting a foot as a reaction to how we are moving our arms/club/body.  Sometimes when observing traces, there is a tendency to only consider one foot, especially when CoP is heavily biased to the trail or lead foot.  Remember: CoP is relative.  Take Justin Thomas at impact, for example.  He has 93% of his pressure on his trail leg even though that toe is barely touching the ground.

 

Additional Notes:

UNDERSTANDING CENTER OF PRESSURE VELOCITY (COPV) (3:30)

Sasho notes how Cordie’s COPV has peaked just prior to SVDS. This is not uncommon as good players are rapidly going from being loaded on the trail side to trying to maximize vertical force under the lead foot.  COPV is not a reliable measure of CHS, however.  Think about if you were at the top of the backswing and you picked your trail foot off the mat. Your COPV could be off the charts (because CoP would immediately move to lead foot), but you’d probably fall over backwards.

Here’s Sasho explaining COPV in our Golf Ground Mechanics Certification.

 

USE PRESSURE AS A BASELINE, NOT A MODEL

We don’t advocate for teaching a specific pressure trace.  Just like in the actual swing, each golfer has a trace that is unique to their swing.  In some ways, there is probably even more variance between what we see in a two dimensional swing and what we gather in ground mechanics data.  As Sasho says in the video, try to capture traces of students playing well.  If they later pick up a characteristic that hampers their swing, you can compare what they are doing differently.  Using date from BodiTrak as biofeedback, you can help them associate a feeling with a desired move.