This is Kwon's part 2 video on torques being generated by vertical GRFs and their reputed effect on clubhead speed at impact.
In this post I am going to dissect this Kwon video where he shows the different vertical GRF patterns produced by two tour-caliber golfers and I am going to specifically analyse his assertion that Player A's vertical GRF pattern is causally responsible for him producing a higher clubhead speed at impact than Player B.
Here is my personal interpretation of Kwon's description of the two patterns - please feel free to correct me if you think that I have misunderstood or misrepresented Kwon's opinions.
Here is a capture image of Player A's vertical GRF pattern, which Kwon suggests is the optimum pattern for maximising clubhead speed. (Player A is my designation and Kwon refers to him as Player M)
The top right hand graph represents the torques generated by the vertical GRFs that can produce a rotation around the golfer's COM.
The middle right hand graph represents the magnitude of the vertical GRFs - the blue graph is the trail foot's vertical GRF, the green graph is the lead foot's vertical GRF and the red graph represents the combined vertical GRF.
The bottom right hand graph represents the magnitude of the moment arm around the body's COM.
The thin vertical black line represents the time point when this image is captured, which is also reflected by the avatar on the left hand side of this image. In this image, Player A is at the ~P2.6 time point. The black arrow represent the size and direction of the vertical GRF (which is mainly due to the trail foot because the lead foot is not being pressure-loaded at that time point). Note that the trail foot's vertical GRF (blue graph) is at its maximum value at P2.6+ and its magnitude is large enough to cause the combined GRF to be greater than the body weight. In other words, Kwon wants a golfer to quickly increase the vertical GRF under his trail foot by his mid-backswing with enough force to cause the combined GRF to be greater than the body weight. Note that the black arrow is pointing straight upwards, and that it is large in magnitude. Note that the black arrow is situated to the right of the body's COM (red dot) and that will promote a clockwise rotation of the body around the COM in the frontal plane axis.
Player A at the P3.8 - P4 time point.
This is the time point when the vertical GRF under the trail foot has decreased to a value so that it is equal in magnitude to the vertical GRF being generated under the lead foot, which is just starting to increase in magnitude.
Note that the trail foot's vertical GRF (blue graph) remained very large from P2.6 to ~P3.5 but it is now decreasing rapidly in magnitude. What is presumably happening is that the golfer is producing a horizontal GRF under his trail foot that allows him to generate a push force off his trail foot that is directed in a targetwards direction. Note that as the trail foot 's vertical GRF decreases in magnitude, the combined vertical GRF (red graph) drops below the level of the golfer's body weight, and Kwon refers to this time period as the "unweighting phase".
Note that the combined vertical GRF (central black arrow) is moderately large in size, but tilted to the right (presumably due to the golfer pushing off his trail foot in a targetwards direction). Now, although the combined vertical GRF (central black arrow) is not large in magnitude, the moment arm is now at its maximum length (see lower right red graph), and that allows the golfer to potentially produce a large counterclockwise torque around his body's COM (see upper red graph). The thin black horizontal dotted line is the tour average when it comes to torque development, and Player A is producing a torque that is slightly larger than the tour average at this time point.
I think that it is important to note that a large amount of torque is being generated (that can potentially cause the body to rotate counterclockwise around the body's COM) even though Player A has not significantly started to increase the vertical GRF under his lead foot. It is also important to note that Player A's pelvis and upper torso is not yet seemingly rotating counterclockwise in that avatar's image, despite the presence of the large torque being generated around the body's' COM in the frontal plane.
Player A at the ~P5.25 time point.
This is the time point when the lead foot is generating its maximum vertical GRF (green graph in middle image). However, the torque arm is now very small in magnitude because the combined vertical GRF (central black arrow) is very close to the body's COM, which explains why the torque being generated (top red graph) is very small in magnitude. Also, note that most of the torque being generated between P4 => P5.2 is due to the lead foot's vertical GRF (note that the green graph in the upper image is superimposed on the red graph) during the P4 => P5.2 time period.
What I can conclude from this image is that Kwon wants a golfer to rapidly increase the vertical GRF under his lead foot during his early downswing so that it reaches its maximum magnitude at ~P5.2 and that action will potentially produce the large torque needed to continue to rotate the torso counterclockwise around its COM. By contrast, in the later backswing as the golfer starts to transition to the early downswing, most of the torque needed is being generated by pushing off the trail foot in a targetwards direction as the body is being unweighted (re-centering phase) and it is mainly due to the large moment arm's magnitude (because the combined vertical GRF is not as large at this time point).
What Kwon never discusses is the role of muscular forces (due to the muscular contraction of pelvic girdle muscles and abdominal oblique muscles and selective back muscles) in causing the pelvis and upper torso to rotate counterclockwise during the early downswing between P4 => P5.2. Kwon also never explains how an optimised torso rotation around its COM in the frontal plane (due to his recommended optimum pattern generation of vertical GRFs) causes the golfer to produce a force/torque at the level of the club handle that can produce linear work and angular work with respect to moving the club handle down the hand arc path between P4 => P5.5. Kwon seemingly presumes that if a golfer optimises his vertical GRF using his recommended optimum pattern that it will automatically translate to increasing the force/torque being exerted by the lead hand on the club handle between P4 => P5.5, but he never presents any evidence to support that opinion. I will discuss this important issue later, but I will first discuss Player B's vertical GRF pattern.
Here is a capture image of Player B's vertical GRF pattern, which Kwon suggests is a very sub-optimum pattern for maximising clubhead speed. (Player B is my designation and Kwon refers to him as Player L)
Note that his lead foot's vertical GRF is equal to his trail foot's vertical GRF at address. Kwon actually prefers that a golfer have a higher vertical GRF under the lead foot at address so that a golfer can push the pelvis clockwise and create a more active pelvis/torso rotation during the backswing loading process. Kwon thinks that Player B's backsing action is too "quiet".
This capture image above is at the P2.6 position where the vertical GRF under the trail foot is at its maximum value. However, the maximum value is small and it does not cause the combined vertical GRF (red graph) to be greater than the body weight. That means that Player B will not have an "unweighting phase" in the P2.6 => P4 time period (note that the red graph in the middle graphs remains flat in the later backswing).
Player B at the ~P4.2 position.
This is the time point when the torque being generated by the combined vertical GRFs (red graph in top graphs) is at its maximum. Note that the maximum torque being generated is less than the tour average (dotted black horizontal line). Kwon claims that it is due to the fact that the vertical GRF being generated under the trail foot (see black arrow at the trail foot) is too large relative to the vertical GRF being generated under the lead foot (see black arrow at the lead foot) and that cancels out some of the counterclockwise rotary torque being generated by the lead foot - because the trail foot's black arrow is to the right side of the COM and it will promote a clockwise (and not a counterclockwise) rotation of the torso around the COM.
Player B at the P5.4 position.
At this time point, the combined torque (red graph in the top graphs) is becoming negative (and it is happening sooner than Player A's torque graph). Note that the central black arrow is just to the right of the body's COM and it is generating a clockwise torque around the body's COM, and not a counterclockwise torque. What is causing that scenario is the fact that the vertical GRFs under both feet are roughly equal (see black arrows at the lead foot and trail foot) and they cause the combined GRF (central black arrow) to be vertical and very close to the body's COM. Also, note that this golfer maintains a lot of pressure (vertical GRF) over his trail foot in his early downswing (see blue graph in the middle graphs) and he does not markedly increase the pressure (vertical GRF) under his lead foot (see green graph in the middle graphs) - as seen in Player A's comparable graphs. In fact, his two graphs seem to be partially reflective of a reverse foot golfer in the sense that he does not markedly increase the pressure under the lead foot in the early-mid downswing as seen in Player A and he actually maintains more pressure under his trail foot than his lead foot in his early-mid downswing, and he also maintains that same pattern all the way to impact.
Okay. Let's accept that player B's vertical GRF generation pattern is sub-optimal in terms of producing a counterclockwise rotation of the torso around the body's COM in the frontal plane in the early-mid downswing. What does that mean in terms of the speed of pelvic and upper torso rotation between P4 => P5.5? Kwon does not discuss that issue and he presents no data on the speed of rotation of the pelvis and/or upper torso between P4 => P5.5.
What about the speed of release of PA#4? Does Player A release PA#4 (lead arm) more actively so that he produces more linear work at the level of the club handle by P5.5 and therefore a greater degree of clubhead speed at that time point?
Here is Sasho MacKenzie's graph on the amount of linear work being exerted on the club handle by ~P5.5/P6 as a result of the lead hand pulling the club handle down the hand arc path in a pro golfer.
The orange curved path represents the hand arc path, and a golfer produces linear work by pulling the club handle down the hand arc path from P4 => P6. Although the peak pulling force peaks at ~P6.2, most of the pulling force has already been generated by P5.5/P6 and it is secondary to the release of PA#4 (release of the lead arm). According to Sasho, the amount of linear work being generated during the release of PA#4 is proportional to i) the length of the hand arc path and ii) the average speed of lead hand motion down the hand path. In this pro golfer, the clubhead speed has already reached 99.3mph due to the release of PA#4 and it happens prior to the release of PA#2.
So, does player A release PA#4 more efficiently than Player B and thereby generate a faster clubhead speed by P5.5 than Player B (secondary to the fact that according to Kwon he has a more optimal vertical GRF pattern that is potentially more conducive to generating a larger counterclockwise rotary torque around his body's COM in the frontal plane axis)?
Here is Kwon's image showing the two players at the P4 time point.
Player A (= Player M) is the blue avatar and his graphs are in red.
Player B (= Player L) is the green avatar and his graphs are in green.
The top graphs are the torques being generated by the vertical GRFs and the bottom graphs show their clubhead speed at every moment of the backswing and downswing.
To the degree that these avatar images are accurately reflective of reality, it would seem that they both rotate their pelvis and upper torso clockwise by roughly the same amount by P4 (although Player B has a much slower backswing action from a time perspective and it takes him longer to get from P1 => P4), and their lead hand position is similar at P4. Note that Player A is producing more torque than Player B at this time point. Also, note that Player A has more pressure-loading of his trail foot than Player B, but his combined black arrow is tilted more leftwards presumably because he is pushing his pelvis/torso targetwards in a re-centering manner during his "unweighting" phase.
Here are Kwon's images of the two players at the P4.5 time point.
Note that Player A is significantly pressure-loading his lead foot and that his frontal GRF torque value has reached its maximum value. Also, note that Player A's combined GRF (central black arrow) is larger than Player B's combined GRF (central black arrow) and that it is located closer to his lead foot. Note that Player B still has more pressure-loading of his trail foot relative to his lead foot, and his combined vertical GRF force (central black arrow) is more centrally located and it is also smaller in magnitude.
So, which of these two golfers is going to be able to i) rotate his pelvis and upper torso faster between P4.25 => P5.5, ii) release PA#4 faster by P5.5 and iii) have a faster clubhead speed by P5.5 due to the lead hand creating more linear work by pulling the club handle faster down the hand arc path (which is going to be roughly of similar length between P4.25 => P5.5)? According to Kwon, Player A is going to do better because he has a more optimum vertical GRF pattern that can produce higher torque values around the body's COM in the frontal plane. However, Kwon is not taking into account the fact that Player B is in a better position to use the muscular contraction of his trail sided lateral pelvic rotator muscles to rotate his pelvis counterclockwise because he has much better pressure-loading of his trail foot during his early downswing between P4 => P4.5, and his pelvis can also rotate more easily counterclockwise away from his pressure-loaded trail leg during the hip-squaring phase because his lead foot is still significantly unweighted.
Here are Kwon's images of the two players at the P5.5 position.
Note that the two players have rotated their pelvis and upper torso by roughly the same amount by P5.5. Note that they have retained roughly the same degree of clubhead lag. Note that Player B has his lead arm angled more vertically downwards, which suggests that he may be releasing PA#4 slightly faster than Player A, but the difference is very small. Most importantly, note that they have an identical clubhead speed at P5.5, which suggests that they are both producing the same amount of linear pulling force (and linear work) with respect to the club handle during their early-mid downswing action between P4.25 => P5.5.
So, why does Player A have a slightly faster clubhead speed at impact. I could imagine that Kwon would argue that it is the end-product of a better vertical GRF torque generation pattern that happens in the early-mid downswing. However, my pertinent question would then be why does it not manifest during the PA#4 release phase that happens between P4 => ~P6.2, and why does it only manifest in the very late stages of the PA#2 release phase just before impact? Secondly, how can Kwon rationally conclude that the difference is not solely due to the fact that Player A can just release PA#2 slightly more efficiently than Player B despite the fact that they both seem to release PA#4 with equal efficiency?
What does it mean to assert that an individual pro golfer can release PA#2 more efficiently than another pro golfer?
Here are capture images of the kinematic sequences of Rory McIlroy and JB Holmes.
Note that they both generate roughly the same clubhead speeds at impact even though Rory McIlroy can release PA#4 faster and get his lead arm speed to be faster than JB Holmes' lead arm speed in his mid-downswing, thereby creating a faster clubhead speed at ~P5.5. However, JB Holmes makes up for that fact by being able to release his clubshaft faster during the PA#2 release phase in his later downswing.
Here are the clubshaft release (PA#2 release) acceleration speeds between Rory McIlroy and J B Holmes that happen in the mid-late downswing.
Note that JB Holmes can accelerate his clubshaft at 247 rads/sec/sec between P6 => P7 while Rory can only accelerate his clubshaft by 149 rads/sec/sec during that same time period, and that enables JB Holmes to reach the same final clubhead speed at impact even though he was generating less clubhead speed in the early-mid downswing. I would like to see Kwon explain what biomechanical/mechanical phenomenon makes that possible, and I would also like to see how Kwon can rationally conclude that this same super-efficient PA#2 release phenomenon is definitely not in play in Player A's golf swing action that makes him able to get a faster clubhead speed at impact than Player B (despite them having similar clubhead speeds at P5.5).
What especially bothers me about Kwon's approach of comparing two individual tour-caliber pro golfers clubhead speed at impact and linking it to a single potentially causative factor (= pattern of generation of vertical GRFs that can potentially produce a counterclockwise rotation of the body's torso around its COM in the frontal plane) is the fact that he has not ensured that confounding variables (other biomechanical/mechanical factors that can potentially cause an increase in clubhead speed at impact) are equally balanced between the two individual golfers. I think that potential major confounding variables are the muscular strength and efficiency of muscular contraction of the golfer's pelvic girdle musculature and core musculature which can potentially increase the speed of pelvic and upper torso rotation in the early-mid downswing, and the strength and efficiency of muscular contraction of the shoulder girdle muscles which can potentially increase the speed of the downward phase of the release of PA#4 during the early-mid downswing.
Consider a comparative example. Let's presume that I select an individual pro golfer from the top 10 PGA tour drivers who have the highest driver clubhead speed at impact and another pro golfer from the bottom 10 PGA tour drivers who have the slowest driver clubhead speeds at impact.
Here is the link to the 2021 stats -
www.pgatour.com/content/pgatour/stats/stat.317.y2021.htmlLet's presume that I choose to compare Bryson DeChambeau (who has an average driving distance of 314 yards) to Brendon Todd (who has an average driving distance of 273 yards). What is causing that large difference? If I measured their vertical GRF patterns and noted that Bryson Dechambeau manifested a pattern that resembles Player A's pattern while Brendon Todd manifested a pattern that resembles Player B's pattern, would you really believe that it explains why there is such a large disparity in their driving distance? Would you really not consider the possibility that the strength and efficiency of muscular contraction of Bryson Dechambeau's pelvic girdle musculature, core musculature and shoulder girdle musculature combined with the relative efficiency of their kinematic sequencing could actually be the major causative factor that is casually responsible for their different clubhead speeds at impact?
I think that it is extremely difficult to isolate what is the largest major factor causing a difference in driver clubhead speeds at impact when comparing two individual tour pro golfers because it is impossible to ensure that there is not a major imbalance in many confounding variables. I think that it would require a large scientific study sample size of ~100 tour pro golfers (50 tour pro golfers with the highest driver clubhead speeds at impact and 50 tour pro golfers with the slowest driver clubhead speeds at impact) where the golf researcher thoroughly studied all the potential causative factors that could potentially increase the speed of release of PA#4 and PA#2 in their study.
I think that what Kwon is really doing by comparing player A to player B in that video is unscientific and more reflective of the behaviour of a swing ideologue, who has a pet theory about golf swing biomechanics/mechanics that he wants to promote. I am used to seeing that type of "swing ideologue" behaviour in golf instructors like Brian Manzella and Michael Jacobs, but I never imagined that Kwon would behave in a similar manner.
Jeff.