|
Post by dubiousgolfer on May 17, 2020 20:36:45 GMT -5
|
|
|
Post by dubiousgolfer on May 18, 2020 6:36:56 GMT -5
I've now read it a few times and all it's given me is a headache!!
I really do not see the point in doing this type of research but this is what I've learned.
1. Clubhead speed is dependent on hand speed (force applied by the hands) and hand path (ie. distance moved) - already knew this! 2. Adding a wrist torque has a small influence on clubhead speed- already knew this! 3. Increasing 'Angular distance' has a small influence on clubhead speed - didn't know 4. His research results seem to show discrepancies with Nesbit's previous research results (methodology differences)- we already had doubts about Nesbit's previous work energy research using his model with spherically segmented joints.
Didn't include the influence on clubhead speed by the shape of the hand path.
DG
|
|
|
Post by imperfectgolfer on May 18, 2020 11:28:24 GMT -5
I think that Sasho's paper is typical of the non-useful golf research that is performed by golf researchers because it does not provide "evidence" as to how a golfer could increase his clubhead speed with practical "real life" suggestions. Sasho talked about the value of increasing dynamic X-factor and increasing lag as a means to increase clubhead speed in his Andrew Rice-video, but he downplays the value of those ideas in his paper when he writes-: "While these studies have provided important insights into the associations between various biomechanical variables and clubhead speed, it could be argued that a firmer understanding of the more direct causes of clubhead speed generation, from a deterministic standpoint, would be of value. In other words, delaying wrist release or increasing x-factor stretch does not guarantee an increase in clubhead speed. This is because these variables do not have a direct mechanical relationship with clubhead speed."
I agree with these statements by Sasho, and it makes more sense to study how a golfer directly applies force/torque to the club handle. However, Sasho's study is not based on direct measurements of forces/torques being applied to the club handle and it is a theoretical exercise based on inverse dynamics calculations. These calculations have a set of assumptions - that a linear force can be applied to the club handle that will pull/push the club handle down the hand arc path and that a hand couple force can also be applied to increase the angular rotation of the clubshaft (representing the release of PA#2). I personally find the assumption that the release of PA#2 is primarily due to a hand couple phenomenon problematic and I would like to see Sasho explain why the release of PA#2 is not primarily due to the laws of physics (that explains the release of PA#2 happening in a double pendulum swing model eg. Iron Byron golf robot). Sasho frames the problem of how best to generate clubhead speed as follows-:"Further, there has also been no research into how the sources of work on the club account for the variability in clubhead speed within a population of golfers. For example, it is possible that golfers with disparate clubhead speeds perform similar levels of angular work on the club and that differences arise due to varying amounts of linear work. Further, if linear work is the differentiating factor, then how important is the magnitude of force applied along the hand path versus the length of the hand path? Having an understanding of the relative importance of each factor would be beneficial to golf instructors trying to improve clubhead speed." I certainly agree that it would be useful for a golfer to know how to apply a linear force to the club handle as the hands descend down the hand arc path, but Sasho's paper does not answer that question. Sasho's study concluded that-: "The results of the regression of clubhead speed with the three sources of external work considered in this study demonstrated that the work done on the club by the golfer predicted virtually all of the variability in clubhead speed (R2 = .99) (Table 2). The linear work component alone predicted 90% of the variability in clubhead speed and had the largest unique contribution (sr2 = .58). Angular work predicted an additional 9% of variability, which was signifcant (p < .001), while gravitational work had no predictive ability (Table 2). It is worth noting that when the work done over the entire swig is used, there are no meaningful changes as linear work predicts 89% of the variability in clubhead speed while angular work predicts 9.7%." This conclusion does not surprise me because it is seemingly the same as stating that most of the clubhead speed in a "real life" pro golfer's golf swing is due to the release of PA#4 and far less is due to the release of PA#2. That conclusion is self-evident to me - based on my study of TGM mechanics and golf biomechanics.
However, what is the best method of releasing PA#4 with maximum efficiency? Sasho's study does not address that question.
Consider some biomechnaical factors that could potentially cause the release of PA#4. Body pivot motions (eg. speed of pelvic and upper torso rotation) that move the left shoulder socket are potentially a major factor. Left shoulder girdle muscles could also potentially play a role in increasing the efficiency of the release of PA#4, as could an active right arm adduction manuever where the right palm can apply a push-pressure against PP#1 thereby helping to move the left hand faster down the hand arc path. Sasho's study did not address these issues, and he seemingly only measured the "average" linear force being applied along the length of the hand arc path. Sasho stated the following in his paper-: "The average force applied in the direction of travel of the hand path was by far the biggest discriminator in separating individuals with different levels of clubhead speed, as it predicted 92% of the variability. From a practical standpoint, knowing that a higher level of average force most likely explains differences in clubhead speed does not suggest a clear path for an instructor, or golfer, trying to increase clubhead speed. The reason is that a higher average force could be the result of several diverse factors such as swing coordination, level of exertion, and the force generating capabilities of the primary muscles involved". Note that Sasho even concedes that measuring the "average" force does not suggest a clear path for a golf instructor, who wants to teach a student golfer how/when to apply a force to the club handle via the hands, and his list of potential factors (swing coordination, level of exertion, and the force-generating capabilities of unspecified muscles) that could affect the application of that linear force are extremely vague from a golf instructional perspective. Sasho concluded that increasing the length of the hand arc path could potentially increase clubhead speed (Duh!), but he was very vague about how best to increase the length of the hand arc path. Sasho wrote-: "Hand path length can be increased by having one or more joints increase their range of motion in the backswing. For example, rotating the pelvis more in the backswing, perhaps by allowing the lead heel to lift off of the ground, would give the muscles in the legs more potential to add energy into the system. Similarly, adding torso rotation would increase hand path length and allow the larger muscles that longitudinally rotate the upper body to do more work". It is interesting that Sasho believes that increasing the degree of pelvic rotation during the backswing could be beneficial because it "allows the leg muscles to potentially add energy into the system". Isn't that type of thinking (in bold) very vague from a biomechanical perspective - compared to my much deeper thinking regarding how best to increase swing power via a pelvic rotary motion?
One of the most interesting comments expressed in Sasho's paper were the following-: "It was determined that for any given golfer, the amount of linear work was multiple times that of the angular work done on the club, while gravity contributed on average 2% to the total amount of work done during the downswing. Participant 42, a scratch golfer with a clubhead speed of 117 ± 1.3 mph, had the highest angular work value of 79 ± 4 J. Nesbit (2005) reported that a scratch golfer with a similar clubhead speed (116 mph) completed far more angular work at approximately 140 J (see his Figure 9). All of Nesbit’s reported angular work values are at least 40 J higher than the highest value in this study. The highest amount of angular work reported by Nesbit was 148 J by a 13 handicap male with 103.7 mph of clubhead speed, and a linear work amount of 140 J (linear/angular work = 0.95). There were 20 participants in this study within ± 3 mph of 103.7; yet, their angular work values ranged from 20 J to 60 J. Given the similar nature of the participants between studies it seems likely that these large discrepancies in angular work were due to differences in methodology?
The bold-highlighted statements are very interesting to me - because it implies that the theoretical calculations of the linear work versus angular work being exerted by a golfer will depend on the methodology used to make these calculations. If true, why should we give greater credence to SMK's theoretical calculations versus SN's theoretical caculations? Also, why should we give credence to either SMK's or Nesbit's theoretical calculations seeing that we do not really know whether they are scientifically legitimate and 100% applicable to what happens in the "real life" golf swing of a skilled pro golfer?
It is also interesting that Sasho made the following comments in his paper regarding this issue of Nesbit's calculations versus SMK's calculations-: "Second, in this study, the total work done on the club by the golfer predicted 99% of the variability in clubhead speed, which makes sense since gravitational work contributed little and was similar between participants. To the contrary, Nesbit (2005) reported that the total work only predicted 43.1% of the variability in clubhead speed (see his Table 4). It seems likely that only methodological differences (e.g., data processing) could account for the 56.9% of unexplained variance. As one example, the speed of the hands (mid grip point) is central to the work calculations. Nesbit (2005), states that unlike previous researchers (Cochran & Stobbs, 1968; Vaughan, 1981), he did not report a significant reduction in hand speed prior to impact. In fact, according to Nesbit’s Table 3, the median peak hand speed occurred exactly at impact (meaning hand speed peaked after impact for half his participants). Vaughan (1981) showed hand speed peaking 60 ms before impact. Osis & Stefanyshyn (2012), showed a graph of hand speed peaking ~80 ms before impact and dropping by ~25 % at impact. On average in this study, hand speed peaked approximately 70 ms before impact and dropped by ~23 % at impact. The black line in top middle image of Figure 5 shows the approximate position of the shaft at 70 ms prior to impact. Collectively, this suggests an issue with how Nesbit processed the positional data (perhaps over smoothing), which would influence all subsequent calculations (e.g., angular velocity, force, work)". It is very worrying to me that Nesbit's study showed that hand speed reached maximum speed at impact and Sasho implies that it represents a flaw in Nesbit's positional data. However, could it be possible that Nesbit's study participants were mainly TGM hitters while MacKenzie's study participants were all TGM swingers?
Sasho concludes his paper with the following comments-: "This study has provided novel insights into the understanding of how amateur golfers deliver energy to the driver and what differentiates golfers with varying levels of clubhead speed. Individual golfers do multiple times more linear work, relative to angular work, during the golf swing and linear work also accounts for the vast majority of differences in clubhead speed between golfers. Methods of training that increase the average force applied in the direction of the hand path during the down swing have the greatest probability in generating increases in clubhead speed".
Sasho thinks that it is a novel insight to conclude that golfers mainly generate clubhead speed by linear work - via a linear force being applied to the club handle down the hand arc path. Duh! I think that such a "belief" is self-evidently true! Did Sasho really harbor a different opinion before he performed this study? Did Sasho really believe that the release of PA#4 is not the main swing power source in a pro golfer's driver swing action? I also think that what "real world" golfers mainly want to better understand is how best to release PA#4 from a biomechanical perspective and Sasho's paper provides no insights regarding that issue?
Jeff.
|
|
|
Post by dubiousgolfer on May 18, 2020 16:29:44 GMT -5
I found this section below particularly difficult to understand but I think he's saying that he didn't include the MOF caused by the 'Net Force' in his work-energy approach. As far as I am aware, the MOF is responsible for Release (ie. also explained by D'Alembert principle) not the 'Couple'.
------------------------------------------------
The golf swing is frequently referred to as a ‘rotational’ skill, which is understandable considering many segments – the club in particular - rotate through large ranges of motion, while the golfer’s center of mass typically only translates a few inches. As such, it may seem unintuitive that linear work was found to far exceed angular work in this study. Although not part of this study’s analysis, it is worth noting that the angular impulse, due to the total torque (TA) applied in the plane of the swing during the downswing, predicted 91 % of the variability in the clubhead speed. So, from an impulse-momentum perspective angular kinetics have a very high predictive ability.
Two key factors result in the work-energy approach softening the importance of angular kinetics relative to the impulse-momentum approach. The first is that only CA contributes to angular work, while TA (CA + MA) contributes to angular impulse. The second is that only an angular impulse can generate angular momentum, while both linear and angular work can contribute to angular kinetic energy. During the backswing, angular work performed on the club can far outpace the change in angular kinetic energy (Figures 4A and 4B). Similar, the linear work done, and change in linear kinetic energy will not be equivalent throughout the swing (Figures 4C and 4D); yet, the total work done will equal the change in energy (Figures 4E and 4F).
Consider a golf club fixed to a pivot - like a planar pendulum - about an axis through the grip end. Two forces act on the club: A contact force at the motionless pivot point and gravity at the translating center of mass. From a work-energy perspective gravity does all the work, and more specifically, all the work done by gravity is linear. Yet, that linear work manifests itself in both linear and rotational kinetic energy in the club. The force at the fixed pivot does no work on the club. From an impulse-momentum perspective, the combined linear impulses of gravity and the force at the pivot equals the change in linear momentum, while the angular impulse – due to the moment of force from the force at the pivot – equals the change in angular momentum. To be explicit, from a work-energy perspective gravity is responsible for all change in angular kinetic energy of a pendulum, while from an impulse-momentum perspective, the force at the pivot is responsible for all change in angular momentum. One benefit of explaining the mechanical sources of clubhead speed using work-energy versus impulse-momentum is that you can avoid the paradoxical thought of increasing clubhead speed by increasing the length of time of the downswing. Consider Figure 2A, participant 42 attained the highest clubhead speed with a downswing time that was shortest in duration. More time allows for more impulse, yet higher average kinetics will decrease downswing time. -------------------------------------------
His pendulum analogy is so completely unintuitive. The force at the pivot causes a MOF on the pendulum (ie. a torque) that changes its angular momentum (ie. makes it rotate quicker) but is not responsible for its increase in rotational kinetic energy. Doesn't make any sense to me at all !
DG
|
|
|
Post by imperfectgolfer on May 18, 2020 17:43:07 GMT -5
Here are some further opinions (that Sasho expressed in his paper), which deserve further discussion. Sasho wrote-: "Having the couple become negative over the final 30 ms of the downswing is likely not advantageous, and although the golfer would theoretically benefit from maintaining its positive direction, it does not seem to be easily accomplished. The ability of a golfer to apply wrist joint torques and trail elbow extension torque would be key to maintaining a positive couple, which is challenging considering these joints have angular velocities over 600 °/s (potentially over 1000°/s) during the fnal 30 ms of the downswing for a mid-handicap golfer (Zheng, Barrentine, Fleisig, & Andrews, 2008). Koike, Iida, Shiraki, & Ae (2006) instrumented the grip of a golf club and were able to report individual hand forces and couples from the swing of a professional golfer. The results support the findings from this study, in that the individual hand forces produced a negative couple in the plane of the swing late in the down swing. Later in the downswing the lead hand couple also became negative, while the trail hand couple hovered just above zero prior to impact. It is important to note that a negative couple does not mean that the club’s angular acceleration becomes negative about the instantaneous axis. Every participant in this study continued to increase the angular velocity of the club after the couple became negative. The torque due to the couple is only part of the total torque applied to the club by the golfer. The net force applied to the grip will also generate a moment of force (MA, Eq. 3) when the line of action of this force does not pass through the center of mass of the club. This moment of force has a strong tendency to be positive late in the downswing and was responsible for the club’s continual increase in angular velocity about the instantaneous axis until impact. Note that Sasho is seemingly implying that there are two forces operant that can induce a club-releasing action (PA#2 releasing action) - a positive hand couple force and a moment of force (coming from the net force applied to the grip when the line of action of this force does not pass through the center of mass of the club). How does Sasho apportion how much of the club-releasing force comes from the hand couple, and how much comes from this moment of force, in his inverse dynamics model?
Also, how does he apportion those two forces in a "real life" golf swing's club-releasing action?
Here is Jamie Sadlowski's driver swing. The hand arc path (in red) is "straightish" between point 1 and point 2, and it will therefore not produce a powerful "moment of force" that can induce the release of the club. However, the hand arc path becomes much more tightly circular between point 2 and point 3 and that can potentially produce a large "moment of force" that can induce the release of the club. However, Sasho seemingly believes that Jamie is also using a hand couple force to manually induce the release of the club (= PA#2 release action) during that same time period. How can a "real life" golfer (like Jamie Sadlowski) synchronize these two forces so that they act in perfect unison, in order to produce an ultra-smooth release of the club? I have watched the club release phenomenon in many amateur golfers, who produce a jerky and inefficient release of the club, and I strongly suspect that they are causing the problem because they are trying to manually release the club using a hand couple action that is superimposed on a club-releasing action that is already in play (due to the law of the double pendulum, which happens when the line of action of the net force applied at the grip does not pass through the COM of the club thereby generating a "moment of force"). DG - seeing that David Tutelman still responds to your e-mail questions, please consider asking him these questions. Jeff.
|
|
|
Post by dubiousgolfer on May 18, 2020 18:19:00 GMT -5
Dr Mann DT is not answering my emails anymore. However there is something on his website relating to 'assisting' the release with an active wrist torque. -------------------------------------------- www.tutelman.com/golf/swing/handhit.php#shaftbendOne interesting observation: Jorgensen found that "late wrist torque" should be applied to a "standard swing" beginning "seven hundredths of a second" (70msec) before impact, and continuing through impact. That corresponds almost exactly to the point of maximum acceleration. So his conclusion might be restated, "As long as inertial acceleration is increasing, don't mess with it. Once it starts to fall off, you might help it along with wrist torque." That actually makes sense! ----------------------------------------- DT has his own view on JS's clubhead speed and mentions the below on his website: ------------------------------------------------ For those who feel that Long Drive competitions change the rules, physics included, here's Jamie Sadlowski just before impact. (Jamie won the ReMax World Championship the past two years running, and won handily.) Yes, his shaft is clearly bent forward, telling us he gets his distance from his huge body turn in the backswing, inhuman wrist cock, and holding that wrist cock very late into his downswing -- and not from forearm or hand strength driving the clubhead through the ball.
Likewise for Tiger Woods, as if there were any doubt-------------------------------------------- DG PS. I just get the feeling that both Sasho and DT have not considered hand path shape . One suggesting an active wrist torque while the other 'holding the lag' (not sure whether DT means active negative wrist torque to keep the lead wrist cocked - surely not).
|
|
|
Post by imperfectgolfer on May 18, 2020 19:06:50 GMT -5
DG, You quoted DT as stating the following-: " One interesting observation: Jorgensen found that "late wrist torque" should be applied to a "standard swing" beginning "seven hundredths of a second" (70msec) before impact, and continuing through impact. That corresponds almost exactly to the point of maximum acceleration. So his conclusion might be restated, "As long as inertial acceleration is increasing, don't mess with it. Once it starts to fall off, you might help it along with wrist torque." That actually makes sense!" That comment about a "late wrist torque" surely means a positive wrist torque. However, both DT and Sasho have claimed that the wrist torque (hand couple torque) should become negative well before impact. Doesn't that claim about a "late torque" contradict DT's latest thinking as expressed in his more recent article - www.tutelman.com/golf/swing/nesbitKwon1.php Jeff.
|
|
|
Post by dubiousgolfer on May 18, 2020 19:51:49 GMT -5
Dr Mann
Yes , that does look like a contradiction by DT.
Jorgensens book was published in 1993 before 'TruTemper Labshaft tool' experiments which was conducted in 1994 (showing forward shaft bend) but DT's comments was in 2010.
Wonder where exactly the club is at 70 msecs before impact (is it before P5.5)? But even so , there is no way to keep applying that wrist torque all the way to impact when there is forward shaft bend. Jorgensen said if you applied it slightly earlier or later , it would cause a decrease in clubhead speed but if timed perfectly it would only cause 0.7% increase in clubhead speed (using his swing model).
I cannot imagine JS using a virtually impossible timing technique like that .
Did Sasho actually state/say that JS was applying an active wrist torque (I've tried googling for any remarks he made on JS's swing but can't find anything)?
DG
|
|
|
Post by imperfectgolfer on May 18, 2020 21:48:44 GMT -5
It is my understanding that the 70 millisecond time point before impact is roughly at P5.5 (point 3 in Jamie Sadlowski's hand arc path).
I have no idea what Sasho really believes regarding Jamie Sadlowski's golf swing action, and he is seemingly determined not to answer any questions posed by me.
Jeff.
|
|
|
Post by dubiousgolfer on May 21, 2020 19:52:43 GMT -5
Thought I'd add this recent video that SMK has posted regarding Jacobs 3D concepts and his book . What a mess! Incredible confusion about definitions and conventions being used for alpha/beta/gamma torques.
DG
|
|
|
Post by imperfectgolfer on May 22, 2020 9:30:05 GMT -5
I have zero expertise when it comes to the mathematical equations that are the basis of inverse dynamics, and I can therefore not comment on the validity of any mathematics-based approach. However, I cannot fathom why using inverse dynamics to estimate the operant forces/torques has any relevance to teaching a "real life" golf swing action, where a golf instructor has to explain to a student-golfer how to practically apply force/torques to the club handle using biomechanical actions. Neither Nesbit or SMK have described how best to move the body/arms biomechanically in order to optimize the performance of a full golf swing action. The only biomechanically-based videos that I have seen produced by Nesbit/SMK is where SMK describes his opinions on how to perform a pelvic motion - using an early extension maneuver where he gets onto his toes in order to maintain his balance. I personally dislike his pelvic motion technique, even though it is reasonable to consider it an optional approach.
Jeff.
|
|
|
Post by dubiousgolfer on Jun 10, 2020 18:10:58 GMT -5
Another interesting point that I have noted below from SMK's article:
"From a practical standpoint, it is important to consider that the couple applied to the grip by the golfer is not controlled independently of the net force applied by the golfer. In other words, there is not a series of actions that would allow the golfer to change the applied couple without also changing their net force during an actual golf swing"
This is very vague and unless SMK can explain to a golf instructor how the hand couple and linear force are dependent on each other , it is meaningless. For example , is the magnitude of the instantaneous 'in plane' hand couple dependent on the instantaneous magnitude and direction (ie. 'mid-hand point' path) of the linear force?
DG
|
|
|
Post by imperfectgolfer on Jun 10, 2020 22:09:55 GMT -5
Another interesting point that I have noted below from SMK's article: "From a practical standpoint, it is important to consider that the couple applied to the grip by the golfer is not controlled independently of the net force applied by the golfer. In other words, there is not a series of actions that would allow the golfer to change the applied couple without also changing their net force during an actual golf swing"This is very vague and unless SMK can explain to a golf instructor how the hand couple and linear force are dependent on each other , it is meaningless. For example , is the magnitude of the instantaneous 'in plane' hand couple dependent on the instantaneous magnitude and direction (ie. 'mid-hand point' path) of the linear force? DG I now can understand how it is possible. I will explain it in the near future in the thread on a major transformation of my thinking. Jeff.
|
|