Post by imperfectgolfer on Dec 30, 2012 11:26:23 GMT -5
About 18 months ago, I had a lot of back-and-forth email discussion with David Tutelman when I implied that he knew very little about golf swing biomechanics, and I have noted that he since written a number of articles on the subject. In particular, he has commented on the work of Sasho MacKenzie and Steven Nesbit.
See this article.
www.tutelman.com/golf/swing/models4.php
I think that it shows that DT is out of his depth when dealing with human biomechanics. DT is an engineer and he wants to reduce everything to some mathematical equation, but he doesn't understand TGM mechanics and golf swing biomechanics.
For example, he simply accepts Nesbit's claim that a lot of swing power comes from the right pelvis, and the right elbow, which I think is nonsensical. I don't think that the right pelvis exerts any useful power in a left hip clearing action. Secondly, this is what DT states regarding the right elbow-: "This bar chart seems to contradict MacKenzie's results -- that a significant amount of clubhead speed comes from left shoulder torque. (And, in so doing, it would contradict my general assertion that later models didn't contradict earlier models; they just refined them and addressed questions the earlier models did not.) But it needn't be a contradiction. We did discuss (and MacKenzie himself mentioned) the possibility of right arm extension adding to left shoulder torque. Nesbit and Serrano's results say that two thirds or more of MacKenzie's "left shoulder torque" is actually due to right arm extension. It also suggests that all swings contain more "C-Motion" (used to be called "Leecommotion") than you might think."
The idea that 2/3 of the "left shoulder torque" action is due to right elbow extension is wrongheaded because the right elbow only extends after P6 and in a swinger it is only helping to maintain the forward momentum of the left arm to a small degree. I don't know where he gets the 66% number!!!
DT also accepts at face value Nesbit's claims about the peak work effort of different body parts during the downswing. I think that Nesbit's claims are nonsensical because Nesbit doesn't really know what is active versus passive, and he doesn't know what active muscular work effort is really contributing to swing power. For example, Nesbit claims that the last two body parts to "fire" pre-impact are the right elbow and right wrist. I believe that Nesbit's claim is meaningless for a swinger who doesn't use any right wrist straightening action to power his swing action.
DT makes the following statement relating to the issue of wrist torque-: "We came to this conclusion based on total work at each of the joints. But the researchers also have the torque-vs-time graphs for each joint (not published in the paper). They must also support this conclusion, because Nesbit writes, "Just before impact the wrists momentarily approximate a “free hinge” configuration as the golfer merely holds on to the club as its momentum carries it to impact. By the time impact is reached, all torque components are in opposite directions because the wrists cannot keep up with the rotational speed of the club at this time in the downswing." That is consistent with my conclusions in my article on hitting with the hands. In a private communication, Sasho MacKenzie has also supported this point, citing the torque-speed relationship whereby the faster a joint is turning the less torque it can exert." This is where Nesbit, DT, SMK and I are in total agreement. One cannot get more CH speed by trying to apply any wrist torque immediately prior to impact (using an active slap hinge action - ala Martin Laird).
The craziest thing that DT states is the following in relation to the hand path-: "You can see that the scratch golfer has a relatively straight path (very little curvature) in the blue curve, and a lot more curvature in the red curve. The 18-handicapper is just the opposite -- much more curvature early in the downswing than near impact. Why does this matter? This is another way of delaying centrifugal release until very late in the downswing, and emphasizing it late for maximum clubhead speed. You don't have to use retarding wrist torque to keep the clubhead lag; just minimze the path curvature early and maximize the curvature late."
It is crazy to believe that the club CF-release phenomenon can be delayed to the red curve area (which is between P6.7 and P7). Any observant student of the golf swing can clearly discern that most pro golfers are using a random release action, which starts between P5.5 and P6. Also, any decrease in the hand radius between P6.7 and P7 can produce some parametric acceleration of the club, which can only contribute an additional 5% increase in CH speed. Many pro golfers do not even have any significant hand arc path radius shortening between P6.7 and P7.
DT finally concludes-: "It is worth noting that the final output of Nesbit's studies is a mathematical model that can be used for forward dynamics studies, even though it was derived from inverse dynamics methods. That is, it consists of a generalized full-body model of any human move (while holding a golf club in both hands), plus a set of about forty input torque curves that constitute a golf swing. Well, four such sets of input torque curves, one for each of the golfers studied. The difficulty of using the model as a forward dynamics model is the sheer number of inputs to consider: how to tweak each one, and how they interact when a real human makes a swing. For instance, changing the firing of some muscles will cause a human to fire other muscles just to maintain balance and stay upright."
He is correct to say that it would be very difficult to create a forward dynamics model of the golf swing using 40 input torque factors - especially when one doesn't have coherent understanding of TGM PA-release mechanics, and if one doesn't realize that a golfer can be a swinger or a hitter.
Jeff.
See this article.
www.tutelman.com/golf/swing/models4.php
I think that it shows that DT is out of his depth when dealing with human biomechanics. DT is an engineer and he wants to reduce everything to some mathematical equation, but he doesn't understand TGM mechanics and golf swing biomechanics.
For example, he simply accepts Nesbit's claim that a lot of swing power comes from the right pelvis, and the right elbow, which I think is nonsensical. I don't think that the right pelvis exerts any useful power in a left hip clearing action. Secondly, this is what DT states regarding the right elbow-: "This bar chart seems to contradict MacKenzie's results -- that a significant amount of clubhead speed comes from left shoulder torque. (And, in so doing, it would contradict my general assertion that later models didn't contradict earlier models; they just refined them and addressed questions the earlier models did not.) But it needn't be a contradiction. We did discuss (and MacKenzie himself mentioned) the possibility of right arm extension adding to left shoulder torque. Nesbit and Serrano's results say that two thirds or more of MacKenzie's "left shoulder torque" is actually due to right arm extension. It also suggests that all swings contain more "C-Motion" (used to be called "Leecommotion") than you might think."
The idea that 2/3 of the "left shoulder torque" action is due to right elbow extension is wrongheaded because the right elbow only extends after P6 and in a swinger it is only helping to maintain the forward momentum of the left arm to a small degree. I don't know where he gets the 66% number!!!
DT also accepts at face value Nesbit's claims about the peak work effort of different body parts during the downswing. I think that Nesbit's claims are nonsensical because Nesbit doesn't really know what is active versus passive, and he doesn't know what active muscular work effort is really contributing to swing power. For example, Nesbit claims that the last two body parts to "fire" pre-impact are the right elbow and right wrist. I believe that Nesbit's claim is meaningless for a swinger who doesn't use any right wrist straightening action to power his swing action.
DT makes the following statement relating to the issue of wrist torque-: "We came to this conclusion based on total work at each of the joints. But the researchers also have the torque-vs-time graphs for each joint (not published in the paper). They must also support this conclusion, because Nesbit writes, "Just before impact the wrists momentarily approximate a “free hinge” configuration as the golfer merely holds on to the club as its momentum carries it to impact. By the time impact is reached, all torque components are in opposite directions because the wrists cannot keep up with the rotational speed of the club at this time in the downswing." That is consistent with my conclusions in my article on hitting with the hands. In a private communication, Sasho MacKenzie has also supported this point, citing the torque-speed relationship whereby the faster a joint is turning the less torque it can exert." This is where Nesbit, DT, SMK and I are in total agreement. One cannot get more CH speed by trying to apply any wrist torque immediately prior to impact (using an active slap hinge action - ala Martin Laird).
The craziest thing that DT states is the following in relation to the hand path-: "You can see that the scratch golfer has a relatively straight path (very little curvature) in the blue curve, and a lot more curvature in the red curve. The 18-handicapper is just the opposite -- much more curvature early in the downswing than near impact. Why does this matter? This is another way of delaying centrifugal release until very late in the downswing, and emphasizing it late for maximum clubhead speed. You don't have to use retarding wrist torque to keep the clubhead lag; just minimze the path curvature early and maximize the curvature late."
It is crazy to believe that the club CF-release phenomenon can be delayed to the red curve area (which is between P6.7 and P7). Any observant student of the golf swing can clearly discern that most pro golfers are using a random release action, which starts between P5.5 and P6. Also, any decrease in the hand radius between P6.7 and P7 can produce some parametric acceleration of the club, which can only contribute an additional 5% increase in CH speed. Many pro golfers do not even have any significant hand arc path radius shortening between P6.7 and P7.
DT finally concludes-: "It is worth noting that the final output of Nesbit's studies is a mathematical model that can be used for forward dynamics studies, even though it was derived from inverse dynamics methods. That is, it consists of a generalized full-body model of any human move (while holding a golf club in both hands), plus a set of about forty input torque curves that constitute a golf swing. Well, four such sets of input torque curves, one for each of the golfers studied. The difficulty of using the model as a forward dynamics model is the sheer number of inputs to consider: how to tweak each one, and how they interact when a real human makes a swing. For instance, changing the firing of some muscles will cause a human to fire other muscles just to maintain balance and stay upright."
He is correct to say that it would be very difficult to create a forward dynamics model of the golf swing using 40 input torque factors - especially when one doesn't have coherent understanding of TGM PA-release mechanics, and if one doesn't realize that a golfer can be a swinger or a hitter.
Jeff.