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Windlass test

Discussion in 'Biomechanics, Sports and Foot orthoses' started by phil s, Aug 6, 2011.

  1. efuller

    efuller MVP

     
  2. Dennis:

    Here is the difference between you and Eric: when Eric writes here on Podiatry Arena, I never have a problem understanding what he writes since he uses scientific principles to explain himself. However, Dennis, I honestly can't follow your logic. You don't use scientific principles or you apply scientific principles incorrectly in your discussions. To me, I believe the difference comes from the fact that Eric has done considerable reading outside of the confines of podiatry to understand mechanics from an engineering aspect, where, from what I have seen from your writings, you have done little to increase your knowledge outside of the narrow confines of traditional podiatric (i.e. Root et al) biomechanics.

    To me there is no contest between you and Eric. Eric is much more intelligent and much more intellectually honest than you. In addition, Eric is one of the smartest podiatrists that I have ever had the pleasure of being associated with. However, in your case, since you seem to only publish on the internet on your website, and don't seem to have even a good grasp of basic physics principles, I can't take you seriously.

    Honestly, I don't know why Eric wastes his time discussing these topics with you since you won't answer his questions time after time. If you want to be taken seriously here on Podiatry Arena, get off your soapbox, stop taking things so personally, learn some physics, learn some biomechanics, and then you will hopefully get some respect from the rest of us.
     
  3. drsha

    drsha Banned

     
  4. :morning::morning::morning:
     
  5. drsha

    drsha Banned

    I am editing Eric’s quote and adding my responses/reactions/replies to it.

    Maybe that can start a dialogue for melding theories or negotiating the broad spectrum of biomechanics.

    If not, I would hope we can come to a place where we can live on the same planet.

    QUOTE=efuller;221721]
    Dennis
     
  6. efuller

    efuller MVP

    Dennis, we may be on the same planet, but you are in a different universe.

    I'll reply to a couple of your points. You really need to figure out how to use the quote system so that your words can be separated from my words. You need a "[some name]" at the beginning and a "
     
  7. drsha

    drsha Banned

     
  8. efuller

    efuller MVP

    I don't know what you know Dennis. Someone who knew nothing of physics could have made the criticism that you did.


    At the bottom of each post there is a button that says quote. When you click that button you get the reply window with the entire text of the post, excluding text that was quoted, with embedded code at the beginning and end. At the end you will see the word "quote" surrounded by square parentheses. At the beginning of the quoted text there is another pair of square parentheses that surround the word quote and have some other text that includes the name of he poster being quoted. Copy the code including the open and close square parentheses. Paste that code at the beginning of the portion of text you want to respond to and then copy and paste the square parentheses around the word quote and paste that at the end of the text that you want to respond to. When this post is submitted, the surrounded text will will have a quote box around it with the original posters name at the beginning. If you don't want the person's name you can just paste square parentheses at the beginning and end the text you want surround with a box.

     
  9. David Wedemeyer

    David Wedemeyer Well-Known Member

    :wacko:
     
  10. Craig Nevin

    Craig Nevin Guest

    I wrote the thesis which is now free on the internet (Google Craig Nevin Thesis) and find a free copy. The simple experiment has profound consequences as laid out in detail in the thesis, and hence the difficulties the establishment had with the author. The simple question is how does the bipedal foot/leg/body move around a weight-bearing stationary big toe.

    The kinematic answer (which I call the kinematic projected transformation of the coordinate frame of reference) changes everything.
     
  11. Craig Nevin

    Craig Nevin Guest

    I wrote the thesis which is now free on the internet. (Google Craig Nevin Thesis) and find a free copy. The simple experiment has profound consequences as laid out in the thesis, and hence the difficulties the establishment had with the author. It was the university that did not want it in the public domain.
     
  12. Craig Nevin

    Craig Nevin Guest

    The measurements can all be found in the thesis "Initiation and control of gait from first principles" by Craig Nevin
     
  13. Craig Nevin

    Craig Nevin Guest

    I wrote the thesis which is now free on the internet (Google Craig Nevin Thesis) and find a free copy. The simple experiment has profound consequences as laid out in the thesis, and hence the difficulties the establishment had with the author.
     
  14. scotfoot

    scotfoot Well-Known Member

    Interesting . But gait initiation without arms ? ( Sorry if I am wrong Craig , but on first quick review I cannot find arms mentioned in your text ) .
    Picture the positions adopted by a group of 800m runners poised at the start of a race . Their arms are pre position in the optimum places for rapid gait initiation .

    Gerry
     
  15. Craig Nevin

    Craig Nevin Guest

    The thesis presents a free-body model of the forefeet of 54 subjects initiating gait from quiet standing (see fig 6-1 page 81, and fig 7-1 page 110). The subjects all had both arms, otherwise this abnormality would have been mentioned in footnote 6-3 page 81. (Incidentally it is VERY important to consider that the all the cadavers who supplied the data for the MTP-1 kinematic motion data in Chapter 4, and published in Nevin, (1997) also had both arms attached).

    The further scenario--which presents runners poised to initiate a 800m race -- also has everyone with only one foot flat on the ground, with the other foot poised on the dorsiflexed forefoot, with the arms AND heel raised as well, but ALSO with and the big toe windlass mechanism poised for instant activation. This race posture was not studied experimentally. The gait studied here in the thesis has both heels starting on the ground (figures 1-1, and 6-1 and A-1 and B-1). The immediately swinging the arms from the alternative poised position presented by Gerry, would ensure that the type of "gait initiated" in the 800m race is "running". (At least one would hope the eager subjects were running before the fifth step). The thesis is developed from first principles, which includes the (presumed) principle that we first need to learn to walk before we can run.

    A rudimentary set of arms are anyway depicted in Figure 7-9, (which you were unlikely to see in a "quick review" of the thesis using a computer search for "arms" that only scores a hit in footnote 7-18 -- once again this unexpectedly occurs in a footnote, not in an arm-note 7-18. There are indeed no arm-notes in the thesis whatsoever except for the last line of page 62 :).

    Albeit that both "arms" in Fig 7-9 are poised downward for the quiet standing experiment depicted in Fig 6-1. Raising one of these arms would assist in immediately applying additional extra (upper body generated) counter-rotating torsional stress into the first metatarsal bone as depicted in Figures 7-9 and Figure 5-1 on page 70. Further comment is supplied in the thesis paragraph immediately preceding Fig.5-1, which, (incidental to the principle premise on the thesis on page 2), refers directly to the single foot running mode of bipedal gait. The upper body torque thus replaces the opposing torsional stresses from the metatarsals of the second foot, which although present in walking, is missing in running. (The foot is not missing, but is not on the ground applying forces).

    Thank you for consulting the thesis which can be downloaded from academia.edu for free.
     
    Last edited by a moderator: Nov 16, 2019
  16. scotfoot

    scotfoot Well-Known Member

    I believe that the arms have an important role to play in gait and that vertical acceleration of the pelvis , produced around a grounded foot inputs energy into the arms and swinging leg , to help produce body segment co ordination .

    The point of my post might more generally be written as - How do you know which part of the body moves first ,to initiate gait , if you are using only force plates as your measurement tools . Would you not need some means of telling if ,for example ,the shoulders move before the hallux .

    Actually ,I believe that your paper contains a very interesting insight into the way in which the foot provides a rigid lever for toe off , and that involves ground reaction toque . In that regard you may have been ahead of your time .
     
  17. Craig Nevin

    Craig Nevin Guest

    Just take some time and read my thesis from the beginning. Take it slowly. there are references there on stopping and starting. Also note that Newton himself said that his "principle" (which in his words cited, is a combination of his first second and third laws) are totally insufficient to explain how motion starts. Newton himself did not even try to explain what you are asking here.

    Does is start in the brain? Decelebrated cats walk just fine, apparently.
    As i say take your time to read my thesis thoroughly. (It is a long journey! But I wrote it twenty years ago and have never seen any need to alter anything. )

    But whatever initiates gait, we know the following preconditions exist.
    Two feet on the ground, with static equilibrium in force.

    Your statement contains several errors (due to haste and lack of preparation for my bombshell post).

    Firstly, nowhere in the thesis is a "rigid lever" mentioned
    Secondly, I am using pressure plates, not force plates as my measurement tools.
    A pressure plate has plenty of sensors to measure exactly which part of the foot the forces are changing under.
    A force plate has only four sensors, and although technically a pressure plate, it cannot measure directly the forces at various locations under the foot. The force plate sensors are also not measuring the foot anyway, but the response of the rigid plate (artificial 2D rigid lever?) interposed between the foot and the sensors.
    Thirdly, the data shows conclusively (i.e. statistically irrefutably) that it is the physical lifting (dorsiflexing) of the great toe that is the first significant mechanical event to be detected directly on the ground. Remembering that the whole gait process is mediated by these forces.

    This is a podiatry arena and I will leave it to the neuroscientist to explain that fact away, in terms of their own models. But it is an experimentally established fact that the big toe that lifts first! (Which is the actual reason I am posting it in this forum, under this topic).

    Thanks for your reply, much appreciated !
     
  18. scotfoot

    scotfoot Well-Known Member

    "Secondly, I am using pressure plates, not force plates as my measurement tools.
    A pressure plate has plenty of sensors to measure exactly which part of the foot the forces are changing under.
    A force plate has only four sensors, and although technically a pressure plate, it cannot measure directly the forces at various locations under the foot. The force plate sensors are also not measuring the foot anyway, but the response of the rigid plate (artificial 2D rigid lever?) interposed between the foot and the sensors."

    Yes, I know the difference , and it was a slip .

    "Firstly, nowhere in the thesis is a "rigid lever" mentioned " .

    I felt it was implied . If not that is a pity since I believe ground reaction torque has a great deal to do with turning the foot into a "rigid lever " (a commonly used term in foot biomechanics ) to facilitate push off .



    "As i say take your time to read my thesis thoroughly. (It is a long journey! But I wrote it twenty years ago and have never seen any need to alter anything. )"

    Yes , I appreciate that is a long document and that it will take some time to fully digest . That is why I wrote " Sorry if I am wrong Craig , but on first quick review " in my first post . Lets just say I was getting a feel for things before delving properly .


    I will get back to you .

    Cheers

    Gerry
     
  19. Craig Nevin

    Craig Nevin Guest

    Before leaving the topic, i would like to cite what one examiner (who sensibly choose to remain anonymous) wrote:

    [B5] The author stresses the fact that in gait the foot does not function as a simple static lever.
    [B6] I think this insight is not new, but it is certainly worthwhile to pay more attention to inter bony kinematics and kinetics during stance phase in gait.
    [B20] Gait initiation is an interesting paradigm because push off function of the foot can be taught to be more prominent.

    Before leaving the topic, i would like to cite what one examiner wrote:
    Before leaving the topic, i would like to cite what one examiner wrote:
    I cite this examiner, because he blandly states the same "common" biomechanical position as you did/do here. But, just as you claim that you knew about the difference between a force plate and a pressure plate (and got it wrong in terms of what the thesis actually states, and what you actually initially said). This impromptu error (blunder) was excused by you as a 'slip'. Fair enough, but biomechanical 'slips' of this type, cannot now be continued to appear scientifically relevant with regard to your next statement, i.e. the one that reads, "I felt it was implied....to facilitate push off".

    The reason for this it that this common said / felt / implied / believed / pity / position, labeled [D20] above, is actually completely disproved for the first step of gait by the objective data presented in the thesis chapter 6. Needless to say, that talking such complete BS (big slip ups) is a commonly accepted biomechanical practice, as can be verified by the fact that the thesis author never anywhere mentions a lever (other than a torque lever-arm) anywhere in the thesis, let alone a 'static lever' or 'rigid lever'. Despite the complete absence of this terminology anywhere in the thesis, examiner B claims that the thesis author 'stresses the fact', when in actual fact, the thesis makes no mention of any lever, whether static, rigid or otherwise, anywhere in the thesis except in section 7.5.2. Unbelievable in rational scientific discussions, but quite common is biomechanics circles, apparently. (Admonishment and chastisement complete. Wear the shoe if it fits, or get blisters if it does not :). Now to move on...

    So Gerry (and any flies on the firewall listening in) read the thesis at your leisure, and I will check back here from time to time to see if anyone here has decided, purely on the basis of the scientific evidence presented, that they should definitely no longer be teaching the implied prominence of push off during gait initiation.

    Ps. Deleting this post or thread won't actually work... the thesis and this post will always be out there, somewhere... lurking on the internet... And just like the subjects studied, it is not going to "push off" by itself either.
     
  20. Craig Nevin

    Craig Nevin Guest

    Complete data on metatarsal function (especially raw cadaver data) that informs my 1997 publication and chapters 2 & 4 of my 2001 thesis can be found here:
    https://open.uct.ac.za/handle/11427/27048
    So in reality do actually know exactly what I am talking about. (period)
     
  21. scotfoot

    scotfoot Well-Known Member

    What on earth ....?
     
  22. the problem with pressure mats and in shoe pressure measurement systems is that they can only measure the vertical component of ground reaction force (GRF), or when placed on a non-horizontal surface, the component of the GRF that is normal to each pressure sensel in the array. During gait the net GRF vector almost always contains anterior-posterior and medio-lateral components. That’s why you need a force plate as oppose to a pressure mat to accurately define the GRF vector.
     
  23. Craig Nevin

    Craig Nevin Guest

    First a pressure mat does not measure the GRF. It measure separate components of force applied to specific anatomical loactions. If you wish to you can add these up to calculate a GRF. The floor based pressure sensor measures the applied forces directly at their anatomical locations. therefore there is no moment arm to apply a shear torque in the horizontal direction.

    On the other hand (I hate that saying):
    The force plate sensors are all displaced from the point of interest in the vertical z direction. Also, because of the low spatial density of 4 force plate sensor per foot plate, there are torques in the x and y directions about each sensor as well. But all these factors need to be taken into account to arrive at a single value (referred to here as the GRF force plate output), and given that the applied load distribution is not actually known priori, numerous assumptions are needed estimate what that applied load actually was in the first place. Remember that a single force plate is really just a stiff pressure plate. and any criticism of pressure plates applied equally to force plates ! The reason that the force plate measures anterior-posterior and medio-lateral components is simply because of the thickness of the plate, which is extrinsic to the anatomical foot ground interface.

    The only information "lost" in a pressure plate is the direction of the GRF vector.
    The information "lost" in the force plate is the actual locations of the foot pressures acting on the plate itself.
    and lo and behold, one actually needs to know the magnitudes and distributions of the actual foot forces acting on the plate, to be able to accurately determine the GRF torques.

    Now to compare the two systems.
    First with a force plate you can (apparently) accurately define [sic] the GRF vector. Major snag though, is this force does not actually impact on any specific part of the foot ! That is why the poster refers to it as a 'definition' rather than a measurement.
    Biomechanics using force plates thus becomes an issue of applied maths, that requires 'definitions" and "input data" to arrive at abstract notions such as accurate (but anatomically irrelevant? ) GRFs.

    Anyone who even raise the issue of in shoe pressure sensors (which have no inertial frame of reference) is basically talking out of the wrong end of their gastro-intestinal tract.

    OK I am out of this arena
     
  24. See ya. Can’t imagine for a minute why they failed you.
     
  25. Darn. And I thought we were going to have a good discussion on how pressure plates have no way of measuring the direction of the GRF vector and thus no way of more accurately determining the joint moments occuring during weightbearing activities.

    https://www.japmaonline.org/doi/abs/10.7547/1000518

    But, in case you didn't read it Dr. Spooner, the author has repeatedly made this claim:

    "I wrote the thesis which is now free on the internet (Google Craig Nevin Thesis) and find a free copy. The simple experiment has profound consequences as laid out in the thesis, and hence the difficulties the establishment had with the author."

    Or perhaps, the reviewers had difficulties with the thesis?

    Maybe, the author should start by spellchecking the article he has repeatedly recommended us reading here on PA:

    "The design and cadaveric assessment of a new artifial first metatarsophalangeal joint replacement for the great toe"

    https://open.uct.ac.za/handle/11427/27048
     
  26. Craig Nevin

    Craig Nevin Guest

    Notice that the spelling error you cite above is due to a transcription error made by the library staff 23 years after the dissertation was published.

    Also the thesis that was failed by four examiners who toiled for thirteen months and three days before coming to the conclusion that it should be failed outright, was actually nominated for thesis of the years in 2011 by dissertation.com.
    Also the data in chapter 6 was presented in orally in A808 on the 13 July 2001. (The A prefix stands for 'Awards session')
    http://www.isb2001.ethz.ch/Old/program/awards.html

    Specifically the foot biomechanics award, which reads

    To recognise outstanding research related to foot biomechanics
    Selection Process: Abstracts are ranked by independent scientists; top ranked abstracts have to be personally presented in final round


    https://isbweb.org/images/conf/2001/HTML/index_Longabstracts.html

    This reply is for the information of objective scientists,
    Clearly there are two camps here, those who think my research can be classified by a single spelling error (that I did not even make, in a thesis I did not even fail), and those other independent scientists who think it is exceptionally good. I present the data so that everyone can come to their own conclusions. The 31 000 odd members of this group can't all be complete and utter idiots.

    I have asked the admin to terminate my membership here, as I am not overtly inspired by the scientific comments of the likes of Kevin Kirby et al.
    But admin haven't done anything about it yet.
     
  27. scotfoot

    scotfoot Well-Known Member

    "I wrote the thesis which is now free on the internet (Google Craig Nevin Thesis) and find a free copy. The simple experiment has profound consequences as laid out in detail in the thesis, and hence the difficulties the establishment had with the author. The simple question is how does the bipedal foot/leg/body move around a weight-bearing stationary big toe. "

    " nominated for thesis of the years in 2011 by dissertation.com."


    Ok , so your thesis has been in the public domain for how long , since 2011? Has it had any "profound consequences" on anything ?Has it changed anything ?

     
  28. scotfoot

    scotfoot Well-Known Member


    What stationary big toe ? Watch the video . Note also the impact absorbing "initial windlass phase" . As far as I am aware Hicks did not mention two phases or highlight the way in which kinetic energy is more evenly controlled during foot strike thanks to a pre dorsiflexed great toe . The bit to look at is 60 seconds in , when the runner is unshod .

     
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