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Chimpanzee Feet Allow Scientists a New Grasp on Human Foot Evolution

Discussion in 'General Issues and Discussion Forum' started by NewsBot, Feb 14, 2017.

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  1. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
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    News Release:
    Chimpanzee Feet Allow Scientists a New Grasp on Human Foot Evolution
    FEBRUARY 8, 2017
     
  2. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
    1
    Chimpanzee and human midfoot motion during bipedal walking and the evolution of the longitudinal arch of the foot.
    Nicholas B. Holowka, Matthew C. O'Neill, Nathan E. Thompson, Brigitte Demes.
    Journal of Human Evolution, 2017; 104: 23
     
  3. Rob Kidd

    Rob Kidd Well-Known Member

    MMMmmmm. Apples and oranges, me thinks. What seems to be being reported is that (while they do not use the term), a substantial midtarsal break occurs in chimpanzee feet during midstance - that does not occur in normal human feet. That is, to a first approximation the midtarsal oblique axis undergoes a substantial "pronation" in chimpanzees. The human foot is noted to undergo a greater range of motion - but in the other direction - ie midtarsal oblique axis supination - presumably as a result of the windlass effect. While I suspect an actual quantification & comparison of the amount of movement has not been undertaken before, they are not the same thing. Unless of course, that I have missed the point. Huge amounts of this sort of work came out of Rob Crompton's lab in Liverpool during the first decade of this century.
     
  4. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
    1
    Chimpanzee ankle and foot joint kinematics: Arboreal versus terrestrial locomotion.
    Holowka NB et al
    Am J Phys Anthropol. 2017 Jun 8. doi: 10.1002/ajpa.23262.
     
  5. scotfoot

    scotfoot Well-Known Member

    So why would a non divergent first ray and the development of a medial longitudinal arch be of benefit to an obligate biped ?

    Perhaps one of a number of reasons might be because pronation of the foot would allow a more liner progression of the COM during gait with less lateral movement since a pronating foot allows the weight bearing tibial head to move towards the medial sagittal plane .

    Any thoughts ?
     
  6. Rob Kidd

    Rob Kidd Well-Known Member

    There no simple answer to your question above, Scotfoot, but there are some guiding principles, such as reducing bending stresses and the evolution of the windlass. I have attached some light reading for you; when you haave digested, we may continue this discussion. Please bear in mind that these were written approaching 20 years ago, Rob
     

    Attached Files:

  7. scotfoot

    scotfoot Well-Known Member

    Hi Rob ,
    I read the papers you referenced ,above ,and in the process of comparing the Chimpanzee rearfoot to that of a human I think I have an idea of one of the ways in which the intrinsic foot muscles contribute to balance .
    The question I asked myself was what type of balance system can take the apparently difficult to balance , tall ,top heavy ,human phenotype and use this shape to advantage ?

    Well , first consider balancing a pencil on your finger . Its very difficult .
    Easier to balance is a long broom handle due to inertia . Easier still is the act of balancing a complete broom on your finger /palm with the broom head in the air and the end of the broom on your hand .
    So can the head of the tibia balance in this way on the talus/calcaneal unit ? I think the answer may be yes , at least for postural stability in the medio lateral direction .

    Previously , Luke Kelly (1) has shown that the intrinsic foot muscles can control foot posture including the condition of the medial longitudinal arch and ,in my opinion ,this could lead to inversion and eversion of the calcaneus, and then via the talus ,to a movement of the tibal head relative to the COG .

    Another paper has shown that the vestibular apparatus has a direct link to some of the intrinsic foot muscles showing the have a key role in balance . (2)

    A third paper (3) indicates that in the absence of strong intrinsics the extrinsics seem take on more of role in postural stability an so enlarge .

    So what I am saying overall is that the intrinsics handle small medio lateral perturbations via calcaneal positioning and with larger perturbations the extrinsics kick in to assist .

    This theory places the intrinsics right at the heart of human balance .

    What do you think ?





    Paper 1 Recruitment of the plantar intrinsic foot muscles with increasing ...

    https://www.researchgate.net/.../51593348_Recruitment_of_the_plantar_intrinsic_foot...22 Dec 2017 - Full-text (PDF) | The aim of this study was to determine the difference in activation patterns of the plantar intrinsic foot muscles during two quiet standing tasks with increasing postural difficulty. We hypothesised that activation of these muscles would increase with increasing postural demand...






    Paper 2
    vestibular modulation of the abductor hallucis and the ... - Scholars' Bank

    https://scholarsbank.uoregon.edu/xmlui/bitstream/.../Final Thesis-Wallace.pdf?...1
    by J Wallace - ‎2016 - ‎Related articles
    explore the vestibular system. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and to elucidate any changes in the association between the vestibular stimulation and electromyography (EMG) responses in response to changes in head position, visual cues, and ...

    Paper 3
    Foot muscle morphology is related to center of pressure sway and ...

    https://www.ncbi.nlm.nih.gov/pubmed/28575753
    by X Zhang - ‎2017 - ‎Related articles
    Gait Posture. 2017 Sep;57:52-56. doi: 10.1016/j.gaitpost.2017.05.027. Epub 2017 May 25. Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing. Zhang X(1), Schütte KH(2), Vanwanseele B(3). Author information: (1)Human Movement Biomechanics Research ...
     
  8. scotfoot

    scotfoot Well-Known Member

    With regard to the above it would appear that babies can hold their bodies in an upright position long before they can balance on their feet . Included below is a link to a video of a man balancing babies on the palm of his hand with the babies holding themselves straight whilst the man moves his hand to keep them balanced . A bit like the head of the tibia balancing on the taloncalcaneal complex with the intrinsics keeping things in balance .

    Note -in the video the authors point out that the activities shown in the video should not be tried at home !

    Video
    Icelandic swim instructor teaches babies to stand on their own ...

    upload_2018-1-13_11-14-37.jpeg ▶ 1:45

    20 Jul 2017 - Uploaded by Business Insider UK
    Snorri Magnusson is Iceland's "Baby Whisperer." The swimming instructor teaches babies as young ...
     
  9. scotfoot

    scotfoot Well-Known Member

    Look at figure 6 in the paper below . Again, Luke Kelly .

    Intrinsic foot muscles have the capacity to control deformation of the ...

    rsif.royalsocietypublishing.org/content/11/93/20131188
    by LA Kelly - ‎2014 - ‎Cited by 50 - ‎Related articles
    29 Jan 2014 - We test the hypotheses that activation of the three largest plantar intrinsic foot muscles, abductor hallucis, flexor digitorum and quadratus plantae is associated with muscle stretch in response to external load on the foot and that activation of these muscles (via electrical stimulation) will generate sufficient ...
     
  10. scotfoot

    scotfoot Well-Known Member

    Further to the above , an extremely interesting paper was very recently published , Koyama et al 2017 (below) , which looked at fatiguing the muscles of the foot and the effect this has on postural sway . They found that the exercises reduced some aspects of postural sway .
    The authors stated -

    "This study revealed that fatiguing foot muscle exercises decreased foot muscle strength and altered postural sway during standing. Interestingly, the fatiguing foot muscle exercises decreased the COP range and velocity while standing compared with the pre-fatigue conditions. The decreased foot muscle strength after the exercises was not associated with changed postural sway during standing after the exercises ".

    What makes this paper so interesting is that the exercises used in the study would have fatigued the extrinsic foot muscles but not the intrinsics ( calf raises and toe curls do not target the intrinsics and a toe grip dynamometer measures extrinsic toe flexor strength )

    Contrary to the interpretation of the authors I believe this paper may show better postural stability with less extrinsic foot muscle input and greater reliance on the intrinsics .

    Paper
    Altered postural sway following fatiguing foot muscle exercises - PLOS

    journals.plos.org/plosone/article?id=10.1371/journal.pone.0189184
    by K Koyama - ‎2017
    7 Dec 2017 - The activities of the intrinsic and extrinsic plantar muscles contribute to postural stability during upright standing, especially in the single-leg standing [9]. Foot muscle strength is considered to be one of the important essentials that provides postural control while standing [10]; however, the relationship between foot muscle ...
     
  11. Rob Kidd

    Rob Kidd Well-Known Member

    Frankly Scottfoot, I would not get toooooo bogged down in the individual function of the intrinsic muscles. I am a fair age now - nearly 63, but what I have learned in my rather extended life is that much early work was very good,in spite of empirical equipment. A classic example is Vern Inmans work - most of his stuff he made himself, at least, so I am told. You should read the 1964 paper of Mann and Inman - phasic muscle actions of the intrinsic foot muscles. It is now 30 years since I read it but my memory says that the summary was that collectively (not individually) they work harder and longer in flat foot. The truth of the matter to me - stand by to be slammed, Kidd, is that the intrinsic muscles have little apart from a collective arch supportive function. That is, to assign a specific contractile function to a foot intrinsic muscles in Homo sapiens is simplistic at best. So: back to the arch - and you made comment earlier about why lose the divergent first ray and opposing first toe.

    1) the posterior component. Raising of the subtalar axis to ~45' (forgive me 42=~45; 45=1/2 of 90), gives us a torque conversion that is vital for the bipedal habit. The act of raising the axis also raised the anterior aspect of the calcaneus, and Bingo, we have the posterior portion of the arch. Now, the windlass is critical in efficient bipedal ambulation. For that one needs all toes in direct alignment with their metatarsals. This couples with a (relatively) huge torsion of the talar head gives you the anterior portion of the arch. Let us not dwell on talar head torsion now - 'cept to say that it aids in M/T jt ROM reduction. This is critical to the propulsive phase of gait, coupled with windlass.

    Of course this is simplistic - there are bipedal mods all over the foot - but there are the critical ones, at least in my opinion.

    Many mistakes were made in the interpretation of the fossil record. In our publication of the OH8 foot in 1996, we mistakenly suggested that the first ray was still divergent with a well developed calcaneus (IE Mortons hypothetic prehuman foot)- at this stage the medial cuneiform had yet to be subjected to multivariate study; A later paper on little foot (StW573) examined both its medial cuneiform and that of OH8 - and both clearly had a non-divergent first ray. It is now clear that the loss of a divergent first ray is an early adaptation, hindfoot changes taking place later (Australopitheis sediba, Science, Bernie Zipfel, ex-pod, was first author, I was third, I think). This is of course a HOX gene issue - that deals with disto-proximal changes.

    At some point - variable I am sure, the calcaneo-cuboid joint became very stable with a huge decrease in its ROM, essentially due to a pronounce process calcaneus- this had certainly occurred in OH8 by its suggested date of 1.8MA. However it had not in the sediba foot, which dates a little earlier at 1.9MA - Mosaisim is the norm - OH8 was East African, sediba was South African - one must expect mosaic evolution. This of course is caudo-cranial, and is down to sonic hedgehog genes

    What has yet to be unearthed from the fossil record is something that demonstrates the third and final body plane/genetic control - that of the Wnt systems (and their upstream and downstream qualifiers); these control dorso ventral changes. Before you jump on me, I know that these are particularly poorly understood.

    A sad, or is it an exciting part of palaeoanthropology, is that frequently it throws up more questions than answers. Thus one has to be incredibly careful in the manner in which to phrase your opinions. And the first rule of science is this: if you are wrong, for Gods sake be the first to say so! If one reads the Little foot paper, one will find a huge mea-culpa with regards to the first ray status. I have attached the relevant papers in case to need some light reading to send you to sleep.

    With regard to the sediba paper in Science, my contribution was largely the big number crunches which produced the canonical variates analysis of the talus and calcaneus - and thus their bivariate plots. To show you how little is needed sometimes to do quality science, this was all done while living in a motorhome in the Northern Territory with no mains power.

    Not sure if this helps - but it has ruled my life for thirty years.

    Rob
     

    Attached Files:

  12. scotfoot

    scotfoot Well-Known Member

    Rob
    At present Dr Karen Mickle and colleagues are working on a paper entitled "Evaluating a foot strengthening exercise program to improve foot function in adults with diabetes " . Knowing what little I know about getting a research project up and running , I can only wonder at the tenacity required to get this one past the powers and that be .
    But I will say this . If Mickle can show a significant improvement in the intrinsics of the exercise group then the wide ranging functions of these muscles will be more evident .
    If this trial is successful then eventually we might see improvements in patients balance ,gait ,the lymphatic system of the foot ,venous drainage ,blood flow into the foot , a reduction in foot ulcers ,less infection ,and reduced levels of foot pain through more normal plantar pressure distribution .
    Can't wait !
    With regard to my/the theory that I put before you , it may not be correct . However I feel it fits the known facts , and ,on balance ,I think it might well have merit .

    Regards
    Gerry
     
  13. efuller

    efuller MVP

    Gerry, you postulated several theories in this thread. I disagreed with most of them and agreed with Rob's analysis of your theories.

    To understand balance you should read David Winter's works on the subject. Postural sway is as you described as trying to balance a pencil on the tip of your finger. You have to move your finger (center of pressure) relative to the center of mass of the pencil to maintain the pencil vertically. Postural sway in bipedal stance, and monopedal stance, is using foot muscles to shift the center of pressure under the foot so that center of mass is accelerated back toward the base of support. The center of pressure is an upward force acting on the body at the bottom of the feet and gravity is a force acting at the center of mass pulling the body downward. When those two forces are directly aligned there will be no rotational acceleration. (At an instant in time there may be constant angular velocity) When they are offset, there will be a force couple that will cause an angular acceleration of the whole body. the center of pressure has to be moved by contraction of the muscles to change the acceleration back toward the center of support. Winter showed that center of pressure moves a lot farther than center of mass which supports the above. So, to understand balance you have to look at how the muscles move center of pressure. The extrinsics are much better at doing this because they create moments at the ankle and subtalar joint. The intrinsics cannot affect the ankle joint and are much weaker than the extinsics at the subtalar joint. The intrinsics are not important for maintenance of upright posture.
     
  14. scotfoot

    scotfoot Well-Known Member

    Hi Eric
    There is ample evidence that the intrinsic foot muscles can invert /evert the calcaneus and thus affect balance . Please see post #9
    Regards
    Gerry
     
  15. efuller

    efuller MVP

    The article in that post does not address change in positions of the foot.
     
  16. efuller

    efuller MVP

    It's not that the intrinsics can cause inversion, its what is the best muscle to cause inversion. The extrinsics are much better at it.
     
  17. scotfoot

    scotfoot Well-Known Member

    Eric you said "It's not that the intrinsics can cause inversion, its what is the best muscle to cause inversion". But in the paper produced by Kelly ,post #9 it was the intrinsics which caused inversion .
    It has long been proposed that the intrinsics and extrinsics both contribute to balance but by different modalities . In my opinion you have neatly described in post #13 the way which the extrinsics make their contribution . The intrinsics make their contribution in the way I have outlined although it is not in the text books . Yet !
     
  18. scotfoot

    scotfoot Well-Known Member

    Practical implications of the balancing effects of the intrinsic action on "talocalcaneal stack " ? With regard to acquired pes planus (flat feet ) , a medial arch support will restore the vertical component of the talocalcaneal stack allowing ,amongst other things , a better intrinsic /calcaneus balancing mechanism leading to better fine control of postural stability and stronger intrinsics . That is what seems to happen in these cases .
     
  19. efuller

    efuller MVP

    The paper showed that after stimulation of the intrinsics there was supination. However, the experimental protocol could not rule out that the extrinsics were contracting at the same time.

    In order for the muscles to contribute to balance they would have to be able to shift the center of pressure in both directions. For the AP direction the distance that intrinsics are able to shift the location of center of pressure is much smaller than the extrinsics.

    What is your theory on how the intrinsic foot muscles contribute to balance?
     
  20. scotfoot

    scotfoot Well-Known Member

    "What is your theory on how the intrinsic foot muscles contribute to balance?"

    Answer . As outlined in the posts above .

    Eric ,in post number #13 you wrote " The intrinsics are not important for maintenance of upright posture." Were you playing devils advocate or is this what you truly believe ?
     
  21. scotfoot

    scotfoot Well-Known Member

    A paper (1) was recently published which looked at the role of two of the intrinsic foot muscles and balance .Here is the conclusion .

    "The findings of this study demonstrate that the vestibular system is able to modulate activity in the abductor hallucis and abductor digiti minimi during standing. This experiment extends the previously reported operational bandwidth of coherent frequencies in the MG (0-20 Hz) (Dakin et al. 2007; Dalton et al. 2014) to intrinsic foot muscles. Elevated cortical demand and lack of visual input increase the corrective response to a vestibular error signal at predominantly lower frequencies, indicating that there are likely different origins of the short- and medium-latency responses. The abductor hallucis and the abductor digiti minimi are likely important contributors to upright standing balance control and they are capable of dynamic vestibular responses which can be modulated by other sensory feedback as well as by cortical activity. "

    (1)
    vestibular modulation of the abductor hallucis and the ... - Scholars' Bank

    https://scholarsbank.uoregon.edu/xmlui/bitstream/.../Final Thesis-Wallace.pdf?...1
    by J Wallace - ‎2016 - ‎Related articles
    explore the vestibular system. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and to elucidate any changes in the association between the vestibular stimulation and electromyography (EMG) responses in response to changes in head position, visual cues, and ...
     
  22. efuller

    efuller MVP

    Which post?

    This is what I truly believe.
     
  23. efuller

    efuller MVP

    The link to the article no longer works.

    To show that the intrinsics are important for balance you would have to show that they contract in response to a perturbation in upright posture. The article appears to show that.

    Additionally, you would have to show that the contraction of the muscles create a mechanical response that is appropriate for the perturbation. For example, if you were standing and someone pushed you from behind, you would tend to fall forward. In response, the subject could contract their soleus muscle and this contraction would shift the center of pressure forward and tend to move the body (center of mass) back over the center of base of support after a push from behind. Conversely, if the push came from in front, the appropriate muscular response is contraction of the anterior tibial muscles to shift the center of pressure postieriorlly.

    Gerry, by what mechanical mechanism are you saying that force produced in the intrinsic muscles help maintain balance?
     
  24. scotfoot

    scotfoot Well-Known Member

    Eric in post #7 I outlined what type of mechanism I had in mind as follows -

    " So what I am saying overall is that the intrinsics handle small medio lateral perturbations via calcaneal positioning and with larger perturbations the extrinsics kick in to assist ."
    So antero posterior perturbations and responses of the type you mention , above , have never really been under discussion .

    Again from post #7 I wrote -

    " So can the head of the tibia balance in this way on the talus/calcaneal unit ? I think the answer may be yes , at least for postural stability in the medio lateral direction .
    Previously , Luke Kelly (1) has shown that the intrinsic foot muscles can control foot posture including the condition of the medial longitudinal arch and ,in my opinion ,this could lead to inversion and eversion of the calcaneus, and then via the talus ,to a movement of the tibal head relative to the COG ."

    How ? Bodyweight causing calcaneal eversion in frontal plane and abductor halluces contraction ,calcaneal inversion .The tibial head can therefore be moved relative to COG to maintain balance .

    Eric , if you think that the intrinsic toe flexors (these are intrinsic foot muscles) play no role in balance are you also saying the the toes play no role in balance ?
     
  25. efuller

    efuller MVP

    Gerry, do you agree that a-p balance is an important part of balance?


    When you say tibial head are you referring to the inferior surface of the tibia?

    I will agree with you that the intrinsics can cause supination, however I question whether they are the most metabolically efficient muscle to use to cause supination. Supination will tend to cause a lateral shift in the location of center of pressure. In one legged standing the ability to create a supination moment is important for maintaining balance.

    Maintaining balance requires the ability to shift the center of pressure both medially and laterally. So, the intrinsic muscles are going to need some help in maintaining balance.

    Most people, given the choice, will choose to balance on two feet and not one foot. In bipedal standing the body has additional mechanisms for medial lateral balance. Flexioin of hip or knee will unweight one side shifting the center of pressure to the left or right.



    The toes play a role in balance when there has been a large perturbation forward and you need to shift the center of pressure anterior to the metatarsal heads. So the toe flexors could give the Achilles tendon a longer lever to shift the center of pressure anteriorly. The long toe flexor has minimal leverage at the ankle joint and the intrinsic flexors have no effect at the ankle joint and you need plantar flexion moment at the ankle joint to shift the center of pressure anteriorly. So, for normal quiet standing the toes play no role in balance.

    In gait, center of pressure under the foot is much less important than where the swing leg is placed for maintaining balance.

    Gerry, what mechanical effect do you think the toes contribute toward maintaining balance?
     
  26. scotfoot

    scotfoot Well-Known Member

    Q
    "Gerry, do you agree that a-p balance is an important part of balance? "
    A
    Yes . Never in dispute

    Q
    "Gerry, what mechanical effect do you think the toes contribute toward maintaining balance? "
    A
    "The toes play a role in balance when there has been a large perturbation forward and you need to shift the center of pressure anterior to the metatarsal heads" Such a perturbation might occur just before a narrowly averted ,disastrous, fall .

    Yes not head . Distal epiphysis ?
     
  27. scotfoot

    scotfoot Well-Known Member

    So I feel that my 3 week old theory still stands .
    A divergent first ray helped with mediolateral balance in early bipeds . As they became committed to terrestrial bipedalism the first ray lined up with the rest of the foot and the "talocalcaneal stack" allowed the intrinsic muscles to continue to help maintain mediolateral balance .
    Maybe part of the story anyway .
     
  28. Rob Kidd

    Rob Kidd Well-Known Member

    This notion is not supported by the available fossil record (sparce though it may be). First remember that the genetics of change lie coincidently with body planes. And then remember that proximo-distal changes are controlled by HOX genes, cranio-caudal (~medio-lateral) by Sonic Hedgehog, and dorso-ventral by Wnt systems (and are still poorly understood) The available fossil record agrees that changes took place in a disto-proximal direction. That is, the forefoot became human-like first, and the hind-foot later. Thus, a foot with no mechanism for torque conversion as yet, does have a non-divergent first ray, and a first toe in apposition. The foot of A. sediba certainly fills this description, and at only 1.9MA old [(Science 333, 1417 (2011) Bernhard Zipfel, Jeremy M. DeSilva, Robert S. Kidd, Kristian J. Carlson, Steven E. Churchill & Lee R. Berger]. This foot also had a mobile midtarsal joint, as evidence by a lack of a facet for a process calcaneus.

    Having said all that, always be ready for and expect a) normal biological variation, and mosaic evolution. By way of example of this, the OH8 foot from East Africa, slightly younger than sediba (1.8MA) does have a very pronounced process calcaneus and thus is on its way to M/T reduction in ROM. Sadly its calcaneal tuber is missing and thus it is foolhardy to speculate as to whether torque conversion was there or not.

    Rob
     
  29. scotfoot

    scotfoot Well-Known Member

    The main thrust of theory is that the intrinsics make an important contribution to balance and that this is via the TC stack . That the intrinsics contribute to balance is so strongly supported by the evidence that I would say it was fact .

    "A divergent first ray helped with mediolateral balance in early bipeds . As they became committed to terrestrial bipedalism the first ray lined up with the rest of the foot and the "talocalcaneal stack" allowed the intrinsic muscles to continue to help maintain mediolateral balance "

    from post #27 above can fairly be called a tag on notion .
     
  30. Rob Kidd

    Rob Kidd Well-Known Member

    You keep using the word theory. I guess I have to ask this: what hypothesis (hypotheses) have you proposed to test your theory? Let us please remember the scientific meaning of the word "theory".
     
  31. scotfoot

    scotfoot Well-Known Member

    ". I guess I have to ask this: what hypothesis (hypotheses) have you proposed to test your theory?"
    As you are aware the theory is still in nappies . Let's not demand that a neonate runs for the bus .

    Ps Post #11" The truth of the matter to me - stand by to be slammed, Kidd, is that the intrinsic muscles have little apart from a collective arch supportive function. That is, to assign a specific contractile function to a foot intrinsic muscles in Homo sapiens is simplistic at best." Possibly the worst sentence you have ever written .
     
  32. efuller

    efuller MVP

    Could you define what you mean by TC stack and how does TC stack contribute to balance?

    Gerry, when I asked you how the intrinsic muscles contributed to balance you agreed with me how they could. But the mechanism that I proposed was a minor contribution to balance. To claim that the intrinsics are important to balance you would have to show that a person who did not have use of their intrinsics could not balance. There are other mechanisms by which a person balances and in my opinion, some of those other mechanisms are much more important than the intrinsics. Specifically, the extrinsics can shift the center of pressure medially, laterally, anteriorly and posteriorly. The intrinsics can only shift the center of pressure laterally. Foot placement is also important for balance. Watch someone "standing" on stilts. They are in constant motion and adjust their balance by changing "foot" placement.
     
  33. Rob Kidd

    Rob Kidd Well-Known Member

    Perhaps you would like to produce evidence that demonstrates that "the worst sentence I have ever written" is false....................
     
  34. scotfoot

    scotfoot Well-Known Member

    Morning .
    Rob , I of course meant sentences but if you include the reference to Mann and Inman 1964 ,which you seem to have preferred over Luke Kelly's work ,then we could extended "worst ever " to the entire paragraph .
    Post # 7 contains links to 3 papers but I suspect you may not have read them .
    Here is a quote from Kelly's modern day paper -

    Abstract
    The aim of this study was to determine the difference in activation patterns of the plantar intrinsic foot muscles during two quiet standing tasks with increasing postural difficulty. We hypothesised that activation of these muscles would increase with increasing postural demand and be correlated with postural sway. Intra-muscular electromyographic (EMG) activity was recorded from abductor hallucis, flexor digitorum brevis and quadratus plantae in 10 healthy participants while performing two balance tasks of graded difficulty (double leg stance and single leg stance). These two standing postures were used to appraise any relationship between postural sway and intrinsic foot muscle activity. Single leg stance compared to double leg stance resulted in greater mean centre of pressure speed (0.24 m s(-1) versus 0.06 m s(-1), respectively, P ≤ 0.05) and greater mean EMG amplitude for abductor hallucis (P ≥ 0.001, ES=0.83), flexor digitorum brevis (P ≤ 0.001, ES=0.79) and quadratus plantae (P ≤ 0.05, ES=0.4). EMG amplitude waveforms for all muscles were moderate to strongly correlated to centre of pressure (CoP) medio-lateral waveforms (all r ≥ 0.4), with muscle activity amplitude increasing with medial deviations of the CoP. Intra-muscular EMG waveforms were all strongly correlated with each other (all r ≥ 0.85). Activation of the plantar intrinsic foot muscles increases with increasing postural demand. These muscles are clearly important in postural control and are recruited in a highly co-ordinated manner to stabilise the foot and maintain balance in the medio-lateral direction, particularly during single leg stance.


    You might also find the paper below informative with regard to grouping the intrinsics together in one ,single function ,mass . The paper helps demonstrate how "simplistic" this notion is .



    The architecture and contraction time of the intrinsic foot muscles
    Tosovic D1, Ghebremedhin E, Glen C, Gorelick M, Mark Brown J.
    Author information

    Abstract


    Although critical for effective human locomotion and posture, little data exists regarding the segmentation, architecture and contraction time of the human intrinsic foot muscles. To address this issue, the Abductor Hallucis (AH), Abductor Digiti Minimi (ADM), Flexor Digitorum Brevis (FDB) and Extensor Digitorum Brevis (EDB) were investigated utilizing a cadaveric dissection and a non-invasive whole muscle mechanomyographic (wMMG) technique. The segmental structure and architecture of formaldehyde-fixed foot specimens were determined in nine cadavers aged 60-80 years. The wMMG technique was used to determine the contraction time (Tc) of individual muscle segments, within each intrinsic foot muscle, in 12 volunteers of both genders aged between 19 and 24 years. While the pattern of segmentation and segmental -architecture (e.g. fibre length) and -Tc of individual muscle segments within the same muscle were similar, they varied between muscles. Also, the average whole muscle Tc of FDB was significantly (p < 0.05) shorter (faster) (Tc = 58 ms) than in all other foot muscles investigated (ADM Tc = 72 ms, EDB Tc = 72 ms and ABH Tc = 69 ms). The results suggest that the architecture and contraction time of the FDB reflect its unique direct contribution, through toe flexion, to postural stability and the rapid development of ground reaction forces during forceful activities such as running and jumping.

    Eric , TC stack is simply a phrase I coined to represent the talus on top of the calcaneus .

    Also you said " Gerry, when I asked you how the intrinsic muscles contributed to balance you agreed with me how they could. But the mechanism that I proposed was a minor contribution to balance."

    What I actually said was " "The toes play a role in balance when there has been a large perturbation forward and you need to shift the center of pressure anterior to the metatarsal heads" Such a perturbation might occur just before a narrowly averted ,disastrous, fall ."

    How can averting a disastrous fall be a minor contribution to balance ?

    Gerry
     
  35. efuller

    efuller MVP

    Gerry, I also asked how TC stack contributes to balance. Podiatrists usually discuss STJ supination that will tend to decrease the talocalaneal angle in the transverse plane, or increase the "TC stack". In normal standing you won't see enough motion of the STJ to significantly change the stack. However an increased supination moment at the STJ may cause the lateral shift in the center of pressure. Is this the mechanism that you are talking about with TC stack?

    I also said in the previous post that the extrinsic muscles can shift center of pressure in all directions. The intrinsics can only shift the center of pressure in one direction. This would make the intrinsics a minor contributor to balance.

    The vast majority of balancing won't have a major perturbation that will get anywhere near a fall. There are even fewer instances where there is a push from behind and the foot can't be picked up and a step taken to maintain balance. So, yes the intrinsics are important for balance when you are standing at the edge of a cliff, or subway platform, and someone pushes you from behind. A very rare occurrence.

    We may be arguing the same set of facts from different viewpoints. The intrinsics are less important than the extrinsics, but they can still aid in balance. Calling the intrinsics important for balance rankles my sensibilities in that it obscures the mechanics of balance.
     
  36. scotfoot

    scotfoot Well-Known Member

    Eric you said
    "Calling the intrinsics important for balance rankles my sensibilities in that it obscures the mechanics of balance."
    But that the intrinsics are important for balance is exactly what the evidence shows .
    I'm sorry that the facts rankle your sensibilities but you are just going to have to adapt .

    At present I feel that my theory of how the intrinsics make an important contribution to balance is simply acting as a distraction so there is little point in discussing it further .

    Things are changing and the importance of the podiatrist is just going to increase with time and improved understanding .

    Gerry
     
  37. Rob Kidd

    Rob Kidd Well-Known Member

    But the evidence doesn't show. The papers you revealed above demonstrated change (in the larger) 4 intrinsics in response to medio-lateral foot disposition. That is, arch support, unless I have missed the point. It says nothing about the other 14/15.
     
  38. efuller

    efuller MVP

    The studies that you quoted show that the intrinsics are active during balancing tasks. That does not mean that they are more important than the extrinsics. (Those studies did not even exclude the possibility that the extrinsics were responsible for center of pressure changes that were seen.) The intrinsics can only change the location of center of pressure in one direction and the extrinsics, with combined activity, can change it in all directions. This is why I think the extrinsics are more important than the intrinsics. I will adapt when the evidence is there to show that I should adapt. Don't lash out at the critics, address their arguments.

    It has been good to have this discussion because I have changed how I think about the intrinsics. I can see that the intrinsic muscles do contribute something. It's just not a lot.
     
  39. scotfoot

    scotfoot Well-Known Member

    Sorry if you feel that I lashed out at you Eric. It's not a personal thing since hitherto most people think exactly the same way about the intrinsics as you do .
    Rob , are you saying that a building whose foundations collapse will not have trouble remaining upright ?

    Recently Kevin Kirby said this -

    "It is time for the podiatric profession to take notice of this important recent foot muscle research in our podiatric medical schools, podiatric residency programs and podiatric seminars so we can stay current in our foot biomechanics knowledge, and continue to be considered the foot function experts within our medical communities. "

    Wise words that seem to have gone largely unheeded .

    The full article can be found here -
    Plantar Intrinsics: Important Or Useless Muscles Of The Foot ...

    https://www.podiatrytoday.com/plantar-intrinsics-important-or-useless-muscles-foot
    23 Nov 2016 - Kevin A. Kirby, DPM. We often think the plantar intrinsic muscles of the foot are relatively unimportant muscles of the foot and lower extremity. Researchers have largely ignored these muscles over the past century. With that in mind, the plantar intrinsics have just recently been getting much more attention ...
     
  40. efuller

    efuller MVP

    I was referring to your comments to Rob.

    Gerry, you weren't implying that I wasn't taking notice of the results of this paper.

    We should think critically about claims made in both new and old research. The statement from the article that the intrinsic muscles of the foot are important for balance is not necessarily supported by the data in the study. I think a better phrasing would be they contribute to balance. When they use the word important it may lead readers to think that they are more important than they are. The extrinsics are more important than the intrinsics for balance because the extrinsics can shift the center of pressure in all directions and the intrinsics in just one.

    Gerry, I am saying that you appear to be overstating the importance of the intrinsic muscles.
     
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