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Gerrard Farrell
02-11-2017, 08:19 AM
Try as I might I cannot trace any paper that has studied , as its principle theme, the role of the toes of the human foot in interacting with the ground to provide traction (in the sense of grip ) . It does not seem possible that this has never been studied before but , as far as I am aware , that is the case . The role of toes in propulsion , particularly with regard to their length , yes . Spreading the toes during swimming to improve traction in water , yes . But traction (grip ) on land , no .
So if the role of the toes in helping to provide traction in the unshod condition has never been properly looked at before , does that mean it doesn't matter ,and is it even less relevant in the shod condition ?
As a starting point in attempting to answer these questions the following might be helpful .

I have found that most people greatly underestimate how much of the foot is actually taken up by their toes and 3 photographs /slides can make a big impression .

Photo 1 This is simply a photograph of the dorsal aspect of a subjects foot .

Photo 2 This shows the same foot with the toes in a curled position . Dots made with a suitable skin safe pen (eye liner pencil or such) are placed on the now easily identifiable MTFJ (explained to the audience as where the toes meet the rest of the foot similar to the knuckles of the hand ) and a photograph is taken of the foot with the dots in position .

Photo 3 This shows the foot with the toes back in the non curled position but with a line drawn across the foot and through the dots on the MTFJ (a join the dots type of thing ) . It can then be explained to an audience that the part of the foot distal to the line is toes and associated interproximal tissue . The reaction to the sequence of images is always the same . " Your kidding ,all of that is toes " ?

In the unshod condition the role of the toes to give traction (grip) is crucial .
In fact I would go so far as to say that in the unshod condition, toes were as important to our ancestors as flight feathers are to bird or a tail fin is to a fish . Regardless of how powerful an animal is ,or the medium through which it moves, the end point of muscular effort must be force delivered through a structure which provides good traction ( in the senses of grip ) between the animal and the medium.
Along this theme , when you walk barefoot on a sandy beach ( provided of course its safe for you to do so ) you feel your toes splaying apart as you walk improving traction ,pressure distribution and function . I believe that this type of activity ,even if undertaken only at a walking pace whilst out with the dog , might be of benefit .
So where does footwear come into this ? As follows .

If I were an experimental biologist/podiatrist/anthropologist (which I am not ) with a keen interest in the foot I would feel compelled to link the structure of the forefoot with one of its primary roles ,traction .

Also , if I were a manufacturer of glove like footwear (which I am not ) I would see that a minimal shoe which allows the toes to spread out when walking on cold wet sand but still allows the foot to stay warm and protected from injury ,would give me a unique selling point . I would , therefore , fund the experimental biologist to see if moving on a sandy substrate , wearing my glove like footwear , might improve foot health .

The experimental biologist /podiatrist , might start his/her research by looking at a comparison between the forefeet of unshod beach and shod indoor , volleyball players.

Any thoughts ?

Gerry

kzelik28
02-11-2017, 09:54 AM
I completely agree that the toes are important for walking and other modes of locomotion. I am uncertain about the statement that "the role of the toes to give traction (grip) is crucial.” At least when walking on a flat, rigid surface... the max traction force (under the foot) is dictated by the friction coefficient multiplied by the normal force on the ground. It would seem to me that the toes might indeed increase this normal force some via toe flexor muscle contractions, and thereby increase max traction. However, given the strength of the toe flexor muscles and the length of the toes, it is not clear to me that this would produce much additional normal force on the ground (compared to the force due to body weight), such that the toes would substantially increase traction (except maybe for a very brief instance of time immediately prior to toe-off, but in this case most of the body weight is supported by the leading leg anyhow).


I suppose two follow-up questions initially come to mind: (1) By what physical means would flexing ones toes increase traction (on flat, rigid surfaces)? (2) Are there other reasons (e.g., sensory, or related to forefoot rigidity) that flexing the toes might be beneficial? If the walking surface were soft/deformable (e.g., sand), then it would certainly be feasible for the toes to "dig in" to help prevent the foot from sliding, as this would provide an additional means (other than friction) to support shear loads.

Gerrard Farrell
02-11-2017, 01:38 PM
Hi Karl ,
Thanks for taking the time to reply .
My initial post is meant to relate primarily to the structures of the foot and the way in which they have evolved to provide traction , on the types of natural yielding substrates which might have been encountered during the evolutionary process .
Surely on a yielding substrate , and with regard to traction ,the interaction between the substrate and the standing foot is about more than just friction .After all, on a yielding soil imprints are created and within these imprints we find ridges and depressions .
During gait on a flat yielding substrate the toes do not provide traction by grasping the soil underfoot ( as fingers might flex around and grasp a branch ) but rather they remain straight and flex around the metarsophalangeal joints (MTFJ) so that as the COM moves forwards the toe flexors act to push the toes into the soil providing grip .
The pedunculated shape of the toes and the grip system provided by the toe nails and associated pulpal tissues also likely contribute to traction since it easier to pull a knife through butter than a spoon .
The toes do not "dig in" but rather are pressed , flat , into the soil and on a sandy substrate this likely activates the toe adductors although this has never been studied .
So what differences might be found between our two groups of volley ball players . Well the musculature in the forefoot area ,the toe adductors and abductors ,might be very different and the cortical aspect of the metatarsals would also likely be different (thicker in the unshod group ).

One last point and that is that when running flat out the print left by a human foot is much the same as a digitigrade animal would leave since only the forefoot comes into contact with the ground . A central pad surrounded by a number of other points of contact ,5 ,with soil compressed between these contacts . When our ancestors were running from predators the last thing they would need would be a friction dependent traction system on a wet slippy soil .

Regards
Gerry

Gerrard Farrell
02-15-2017, 03:31 PM
What I was driving at then , in the first post , was that very little seems to be known about the exact roles that the toe abductors and adductors play in balance and gait in the unshod condition . If we are to understand and prevent /treat patholgies in the forefoot area then an understanding of what role/s each anatomical element has evolved to play during locomotion would be of great value .
An elegant example of this ,concerning a revised understanding of how toenails function ,which in turn has led to a new corrective technique , can be found be found at the link below (link 1)

With regard to the passage in your post -
" I am uncertain about the statement that "the role of the toes to give traction (grip) is crucial.” At least when walking on a flat, rigid surface..." -

You might be interested in the following .It relates to grip ,torque ,flat rigid surfaces and the unshod condition .

First I found myself a suitable surface such as linoleum . Next I took off my shoes and socks and stood next to a wall for support . Then , taking most of my weight initially on the right foot which was kept flat on the ground ,I put my left foot into toe off position so that only the ball of the foot and the toes were in contact with the ground . Then I carefully transferred some weight onto the left foot and finally,with the ball of the foot and toes under some pressure , rotated the foot outwards producing torque . I found that the toes played an important part in resisting the outward rotation and that they also began to become spaced out from each other possibly engaging the adductors .( please note that I am not suggesting that anyone copy the above exercise sequence or injury may result )
So perhaps the toes can significantly aid grip on a flat rigid surface ?

Regards
Gerry

Link 1 A Novel Nonsurgical Treatment for Pincer Nail That ... - NCBI - NIH (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4350317/)

https://www.ncbi.nlm.nih.gov › NCBI › Literature › PubMed Central (PMC)
by H Sano - ‎2015 - ‎Cited by 1 (https://scholar.google.co.uk/scholar?espv=2&um=1&ie=UTF-8&lr&cites=3843535113570299455) - ‎Related articles (https://scholar.google.co.uk/scholar?espv=2&um=1&ie=UTF-8&lr&q=related:Py4ZZtL6VjWjhM:scholar.google.com/)
6 Mar 2015 - Hitomi Sano, MD, PhD corresponding author ... This is the first report to show that pincer nail can be treated by a nonsurgical method that ...

Gerrard Farrell
03-02-2017, 01:12 PM
"First I found myself a suitable surface such as linoleum . Next I took off my shoes and socks and stood next to a wall for support . Then , taking most of my weight initially on the right foot which was kept flat on the ground ,I put my left foot into toe off position so that only the ball of the foot and the toes were in contact with the ground . Then I carefully transferred some weight onto the left foot and finally,with the ball of the foot and toes under some pressure , rotated the foot outwards producing torque . I found that the toes played an important part in resisting the outward rotation and that they also began to become spaced out from each other possibly engaging the adductors .( please note that I am not suggesting that anyone copy the above exercise sequence or injury may result )
So perhaps the toes can significantly aid grip on a flat rigid surface ? "

A final point related to the above quote , taken from my last post , might be of interest .

Several studies have looked at the control of angular momentum through the coordination of body segment movement during walking . I feel that it is likely that in the unshod condition ,where walking or running produces excessive torque , the subsequent outward rotation of the foot will necessitate increased eccentric activity in the toe adductors , such as the transverse head of the adductor hallucis , to control toe separation . It is also plausible that stretch receptors in these muscles will send proprioceptive afferents which might then help produce adjustments to body segment movements ,such as arm swing , to counterbalance the torque being produced in the leg and foot and so produce more efficient movement with less internal , torque related , joint strain .

Gerry