Chimpanzee Feet Allow Scientists a New Grasp on Human Foot Evolution

You wrote "I was referring to your comments to Rob."
I slammed a paragraph that Rob wrote which contained the phrase " stand by to be slammed, Kidd" . To my mind Rob wrote a provocative paragraph , eyes wide open .Given the context I very much doubt he was offended .

Eric you also wrote -
"Gerry, I am saying that you appear to be overstating the importance of the intrinsic muscles."

Given the evidence I don't think so .
Here are some quotations from recent papers -
1 Tosovic

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.

2 Kelly

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

3 Kelly 2014

Our following experiment has shown that activation of the plantar intrinsic foot muscles under load produced significant alterations in metatarsal and calcaneus segment angles, which countered the deformation occurring owing to the initial load and ultimately increased LA stiffness. This active arch buttressing mechanism may have important implications for how forces are transmitted during locomotion and postural activities.

4 Wallace 2016

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. "

5 Zhang 2017

Our results showed that larger abductor hallucis correlated to smaller COP sway, while larger peroneus muscles correlated to larger COP sway during single-leg standing. Larger abductor hallucis also benefited open-loop dynamic stability, as well as supported a more efficient transfer from open-loop to closed loop control mechanisms. These results suggest that the morphology of foot muscles plays an important role in balance performance, and that strengthening the intrinsic foot muscles may be an effective way to improve balance.





Eric , you keep saying that the extrinsics are more important than the intrinsics . Who said it was a competition ?

 

You have my assurance that Rob was not offended; I just don't agree with you. It is not a question of following the literature, wherever it may take you. To me. all of the above may loosely be lumped together as arch support. I think that you are making too much of a simple issue. As always, I stand to be corrected. Rob

 

Morning Rob , morning Eric .
Please see the abstract below which relates to foot posture and therefore ,to an extent , the inversion eversion of the TC stack . Easier to balance on an intelligent /cooperating structure than a foot with all the responsiveness of a dead haddock .

Gerry
Contributions of foot muscles and plantar fascia morphology to foot posture
Angin, S, Mickle, KJ and Nester, CJ 201
Gait & Posture . (In Press)

Background: The plantar foot muscles and plantar fascia differ between different foot postures. However, how each individual plantar structure contribute to foot posture has not been explored. The purpose of this study was to investigate the associations between static foot posture and morphology of plantar foot muscles and plantar fascia and thus the contributions of these structures to static foot posture.
Methods: A total of 111 participants were recruited, 43 were classified as having pes planus and 68 as having normal foot posture using Foot Posture Index assessment tool. Images from the flexor digitorum longus (FDL), flexor hallucis longus (FHL), peroneus longus and brevis (PER), flexor hallucis brevis (FHB), flexor digitorum brevis (FDB) and abductor hallucis (AbH) muscles, and the calcaneal (PF1), middle (PF2) and metatarsal (PF3) regions of the plantar fascia were obtained using a Venue 40 ultrasound system with a 5–13 MHz transducer.
Results: In order of decreasing contribution, PF3>FHB>FHL>PER>FDB were all associated with FPI and able to explain 69% of the change in FPI scores. PF3 was the highest contributor explaining 52% of increases in FPI score. Decreased thickness was associated with increased FPI score. Smaller cross sectional area (CSA) in FHB and PER muscles explained 20% and 8% of increase in FPI score. Larger CSA of FDB and FHL muscles explained 4% and 14% increase in FPI score respectively.
Conclusion: The medial plantar structures and the plantar fascia appear to be the major contributors to static foot posture. Elucidating the individual contribution of multiple muscles of the foot could provide insight about their role in the foot posture.​

 

And that is exactly right - contributing to arch support. Let us not forget that the arch is a misnomer - it is actually best modeled on a half dome, with maximum height on the medial side. Thus. medial muscles (which are in fact the only ones tested), work to support it.

You may like to note that PF3 - the anterior regions of the plantar fascia was the greatest input, yet has no muscle input at all - well, apart from some very vague, very minor, accessory attachment by some groups of intrinsics.

 

So body weight gives foot pronation and TC eversion in single leg stance . Also the medial muscles can contract giving foot supination and TC inversion or relax giving eversion with a resultant change in the relative positions of the distal end of the tibia and COM . So small mediolateral balance adjustments . No ?

 

I suppose in theory contraction of abductor hallucis will aid arch shortening, and thus will produce a supination moment around the ST axis (if this takes place weightbearing) I do see that single stance or double stance makes any difference in this thought experiment. I have not data as to its power, in this respect, but intuition tells me that is is very weak - measurable even.

 

They are using correlational tools and it appears that they are inferring causation. "
Larger CSA of FDB and FHL muscles explained 4% and 14% increase in FPI score respectively." I could see "flatter" foot posture creating a need for increased FDB and FHL cross sectional area. If that was how it worked the FPI would explain the increased CSA of the muscles and not vice versa.

Gerry, what was your point about the dead haddock?

 

No. Are you familiar with Kevin Kirby's paper on rotational equilibrium. Are you familiar with my paper on center of pressure and the location of the STJ axis. The ground does not always cause pronation. For maintaining balance, it's not the distal end of the tibia that matters, it's the location of center of pressure under the foot relative to the center of mass. The small medial lateral adjustments of center of pressure under the foot are what are used in balance.

On the point the medial muscles can contract and cause supination and the muscles can relax and cause pronation. One of the earlier studies you noted said that at relatively small loads the muscles were not active. In this state, the muscles would not be able to relax further to cause pronation. So a more efficient explanation of balance would have the active contraction of muscles able to shift the center of pressure under the foot in all directions.

 

"So body weight gives foot pronation and TC eversion in single leg stance . Also the medial muscles can contract giving foot supination and TC inversion or relax giving eversion with a resultant change in the relative positions of the distal end of the tibia and COM . So small mediolateral balance adjustments . No ?"

It's possible the answer is no but ,on balance , I think the system outlined above may well exist .

Here is a question to which I cannot find a definitive answer and which has its root in the paper by Wallace 2016 , above . In a habitually unshod individual does forceful contraction of the abductor digiti produce any forces that would tend to cause foot eversion ?
Also " So a more efficient explanation of balance would have the active contraction of muscles able to shift the center of pressure under the foot in all directions."

What I am saying is that there is more than one balance system in play . The classical understanding of how we balance on our feet (with which I am familiar ) does not exclude the existence of a second , mediolaterally orientated ,intrinsic driven system capable of fine control .

 

If we are discussing balance, the key variable is shift of location of center of pressure. Yes, eversion will tend to cause a medial shift in the location of the center of pressure. So, muscles that create an eversion moment like peroneus brevis will shift the center of pressure more medial. The abductor digiti minimi's (is that the muscle that you are referring to?) affect is much more complex. It's a muscle that I haven't thought that much about. From a quick look online it's origin appears to be distal to the distal aspect of the bones of the subtalar joint. If this is true, the muscle would have no direct effect at the STJ. It's distal attachment may plantarflex and or abduct the fifth toe. If, the fifth toe plantar flexes, it is possible that this might shift the center of pressure distally. It also might not. Regardless the affect would be very small. It would seem that maximum contraction of the abductor digiti minimi might have the same or less affect as a 2% change in the activation of the Gastroc/Soleus, or peroneus brevis muscles.

In a previous post I said that we may be saying the same thing from different perspectives. I believe both the intrinsics and extrinsics can contribute to balance and that the extrinsics are more important than the intrinsics. Would you agree that is consistent with what you said directly above.

 

You said
"In a previous post I said that we may be saying the same thing from different perspectives. I believe both the intrinsics and extrinsics can contribute to balance and that the extrinsics are more important than the intrinsics. Would you agree that is consistent with what you said directly above"

I would agree that you can maintain balance using the extrinsics alone and that you can not maintain balance using the intrinsics alone . However ,you can do it best using both . (see Wallace 2016)

 

So for the purposes of keep the body balanced and avoiding falls we have a stepping strategy ,a hip strategy ,an ankle strategy , and , in my opinion an increasing likely "sub ankle " strategy which involves the intrinsic foot muscles and their effects on the calcaneus (inversion/eversion ) . This sub ankle strategy ,which can function independently of the extrinsic foot muscles , is likely only effective for fine mediolateral control and may be difficult skill to master initially .
Strengthening atrophied intrinsics may help this system regain former levels of efficiency .

 

Hi Eric and Rob ,
With regard to the thread above I thought you might be interested in this blog post about a recent scientific paper (below ) .

Here is quote from the paper discussed in the blog (Vestibular evolked responses indicate a functional role for the intrinsic foot muscles during standing balance ;Jonathan W.WallaceaBrandon G.RasmanbBrian H.Dalton) -

"The current findings indicate that the vestibular control of standing balance can be represented by the intrinsic foot muscles and implicate a postural role for these muscles in modulating quiet standing."

Blog
Is balancing in your feet? The contribution of foot muscles to postural ...


https://ispgr.org/is-balancing-in-your-feet-the-contribution-of-foot-muscles-to-postura...

 

Gerry,
You did see the following quote in the article?
"Even though the feet provide an excellent source of sensory information, it is uncertain whether foot muscles play an active functional role in maintaining quiet standing balance; or whether the activity of these muscles is simply a by-product of preserving rigidity of the feet for the plantar flexors to produce postural responses to keep the body upright. "

The above point is what I have been trying to say throughout this thread. The intrinsics are contributing to postural control by making the foot more rigid so that the extrinsics can shift center of pressure and affect balance. As I said earlier, the intrinsics may contribute a small percentage to balance.

 

I did see that sentence and it appears in the first paragraph of the article where the researcher /author lays out the rational behind the experiment . It is clear that , pre experiment , they saw things as you did/do .

The second paragraph lays out the method , results and conclusion . The post experiment conclusion is represented as "The current findings emphasize that foot muscles provide an active role in balance control during standing. "

So for the authors " it is uncertain whether foot muscles play an active functional role in maintaining quiet standing balance; or whether the activity of these muscles is simply a by-product of preserving rigidity of the feet for the plantar flexors to produce postural responses to keep the body upright. " is not their post experiment view .

They asked , the intrinsics , an active or passive role ? And answered active .

But have they changed your mind ?

Gerry

 

I find this topic quite interesting. But the other day I stumbled on a entirely different advice from another blogger. I need to review it of course. Thanks for posting. I would love to share it for Podiatrist south west Victoria

 

No, they have not changed my mind, because from the experimental setup described (it was not described very thoroughly) I don't see how they could make the distinction between making the foot more rigid or altering center of pressure. They only showed the muscles were active.

"The current findings emphasize that foot muscles provide an active role in balance control during standing. " Another interpretation of that quote is that "active role" is that either possibility (making rigid, altering center of pressure) is true. The muscles were active. You have to look at what the intrinsic muscles can mechanically do. Balance is a center of pressure and center of mass issue. The intrinsic muscles have a small effect compared to the extrinsic muscles in their ability to shift the location of center of pressure.

 

Eric ,
I believe the researchers explain what they mean by "active role" in the following quote from the paper abstract .

"The current findings indicate that the vestibular control of standing balance can be represented by the intrinsic foot muscles and implicate a postural role for these muscles in modulating quiet standing."

 

So a "postural role" means making the foot rigid. It sounds like we are in agreement that the intrinsics contribute only a small amount toward balance.

 

The authors attribute "control " and "modulation" to the intrinsics . I do not believe that the authors' intended meaning is that the intrinsic act simply to make the foot rigid . We are not in agreement .

Gerry

 

So you would be on shaky ground quoting an ambiguous statement supporting your ideas. Additionally, the experimental set up could not address the question of whether the intrinsics made the foot more rigid or the intrinsics shifted the center of pressure to help maintain balance. The results just showed that the muscles were active, not what they were doing when activated. With that experimental set up the authors could not make the claim for control and modulation as you interpreted above.

 

Eric
I don't think that the statement - " The current findings indicate that the vestibular control of standing balance can be represented by the intrinsic foot muscles and implicate a postural role for these muscles in modulating quiet standing." - is ambiguous at all .

The paper relies upon the perceived truth that muscles control by vestibular apparatus affects are directly involved in postural control .

It is may not be a game changing paper but more a confirmation of the earlier work of Wallace .

Do you remember this from post 41 ? It's a link to some of Luke Kelly's work .

2 Kelly

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

 

As I wrote in post 19, The experimental protocol does not preclude the extrinsic muscles from acting. The intrinsics were stimulated, but the extrinsics were not monitored for activity. Therefore you cannot assume that the motion seen was solely from the intrinsics. So, that study was not conclusive either. You have to look at mechanically what the muscle can do by its placement and what force it can develop. The extrinsics have much better leverage and placement to shift the center of pressure which Winter showed is what is required for maintaining balance. Yes, the intrinsics can aid in balance by making the foot more rigid.

 

I agree that the work done around the vestibular apparatus and activation of the intrinsics is indicative and not definitive and indeed Wallace uses the word indicative in the title of his paper .

I would contend however , that the work of Kelly and his colleagues (2012) is more persuasive .
Quote
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

Finally , it has recently been demonstrated (paper 1) that push off requires the participation of the intrinsics . If your ability to run or walk is impaired ,won't that affect balance ?

Quote
"In conclusion, we have shown that the PIMs actively contribute to stiffening of the MTP joint in late stance during walking and running, to assist propulsive push-off, and that the windlass mechanism cannot support this function without them."

Paper 1
The functional importance of human foot muscles for bipedal locomotion
Dominic James Farris, Luke A. Kelly, Andrew G. Cresswell, and Glen A. Lichtwark
PNAS January 17, 2019

 

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