Mandrin... so sorry I didn't respond to your earlier post....we've been on a top secret research trip and we hunkered down without Internet access for several days.....
I did an awful job asking my original question - you did a great job thoroughly answering what you thought I was asking.
I was struck by a comment you made a while back....that we see in 2D as we make our way through everyday life. That being said, is looking at a 3D avatar of a golfer an improvement over video or is the avatar subject to all the vagaries of 2D....?
Also, I would love to get your basic thoughts on 2D versus 3D modeling of the golf swing and the
corresponding pros and cons of both. I see this being a fairly big issue moving forward.
As far as fishing or trying to write a chapter in a book - not quite. I'm just trying to learn from the best at all times.
Michael,
Take what I post with a grain of salt, since I am not the one who knows all, I am simply trying to answer your questions.
I can't quite connect with your remark -
“I was struck by a comment you made a while back....that we see in 2D as we make our way through everyday life".
but it explains perhaps the nature of your questions. You have to further explain to me what you think I have said in an earlier post.
Multi-body systems, such as humans, have a very complex behaviour when driven by internal and/or external forces/torques. If one is interested in studying the motion as they are generated by known external forces/torques, one uses an approach called 'forward dynamics'. Here basically forces/torques are the input and motion as the output. If one is interested in the internal forces/torques when motion and external forces are known then one uses a process known as 'inverse dynamics'. Hence basically motion is input and forces/torques are the output.
There are presently several sophisticated multi-body software packages available but scientists seems to agree that 3 degrees of freedom is a practical limit to meaningful forward dynamics mathematical modeling. Nevertheless, the great advantage of even simple mathematical forward dynamics modeling is that one is able to play around with it and study various trends which is difficult or impossible with 'inverse dynamics'.
'Inverse dynamics' has been used extensively for human motion such walking, sprinting, jumping, rowing and kicking, etc., but seemingly, up to at least 2004, has not been applied to sports such as batting, puck shooting and golfing due to the indeterminacy caused by the two arms and the implement (bat, stick or club) forming a closed kinematic chain. (1)*
Using 'inverse dynamics' allows one to develop and use complex multi segment models as the very complex time histories of the joint forces are not the input but actually the desired output of the process. Recently Prof. Nesbit, used a sophisticated 3D model of a golfer consisting of 15 segments. Also a model for the golf club consisting of 15 segments. Getting indeed rather sophisticated. He uses some mixed form of forward/inverse dynamics.
The complexity however of a sophisticated inverse dynamics approach does not come without some price to pay. The whole process of gathering motion data, low pass filtering, processing and interpretation is a rather complicated affair and validation becomes indeed a very important aspect of it all to try to establish some confidence in the output generated.
Some rather puzzling finding by Dr. Nesbit concerns hand speed through the impact zone, measuring for his test subject golfers, almost constant hand speed, contradicting what everybody can witness for himself on TV, from slow motion impact video clips of pros. Also prof. Grober measures hands slowing down through impact.
Seeing the impressive complexity of the model used by Dr. Nesbit and comparing it with the relatively simple double or triple pendulum 2D mathematical models it is rather paradoxical that it really does not produce all that much new information over the information produced by these relatively very simple 2D models..
From the abstract of (2)* -
“The study highlighted the importance of the wrists in generating clubhead velocity and orienting the club face. The trajectory of the hands and the ability to do work were the factors most closely to skill level.”
However, the importance of the wrist joints in generating clubhead speed and the trajectory of the hands can be very conveniently studied also with simple 2D math models. In effect in a more recent paper, Dr. Nesbit, dealing with hand path, also uses a simple 2D model. (3)*
Dr. Nesbit is the probably the first researcher using complex 3D modeling to study the golf swing. Hence he is breaking new grounds. It would be very interesting to see other independent studies of equal complexity being done in the future to have the possibility to compare. Even the research efforts, using very simple 2D models, frequently did not quite agree. Progress in science is slow.
Michael, when looking for immediate practical information as an instructor there is not a whole bunch of useful information coming out of modeling. But slowly with time the continuing scientific research efforts will form a solid frame on which to build, e.g., kinetic chain action. It also allows to discard existing pseudo science in golf.
There is a growing awareness, due to biomechanical research, of the surprising large forces occurring in various parts of the body and this is increasingly becoming an integral part of golf instruction. There is likely going to be a somewhat more holistic approach to golf instruction, integrating optimum swing techniques, striving for longevity (reducing risks of injury), and mental aspects.
(1)'Research methods in biomechanics'. G Robertson et al.
(2)'A three dimensional kineamatic and kinetic study of the golf swing'. S Nesbit
(3)'Kinematic analyses of the golf swing hub path and its role in golfer/club kinetic transfers'. S Nesbit et al.
on how we view video, still pictures, and 3D avatars as it relates to golf instruction....
