The intrinsic foot muscles don't really support the medial arch of the foot with heel down as much as spread load.

[Gerrard Farrell]

During single leg stance recent research has shown that the intrinsic foot muscles are active and that the greater the load the more active they become. Kelly et al 2014

However, there seems to be a misconception around the idea that the intrinsic foot muscles somehow exert forces on the medial arch of the foot without involving the toes. This is simply not true since the plantar intrinsic foot muscles all act on the toes and generally act, at least in part , to plantar flex them around the MTPJ .

The intrinsic foot muscles and the extrinsic toe flexor muscles have a large number of points of origin but they do NOT insert into the heads of the metatarsals.

The intrinsic foot muscles will have little or no impact on every day foot mechanics if the toes plantarflex against nothing, or for example if a person stands on a board with their toes hanging over the end.

A rough analogy would be trying to lift a heavy load with a lever . If the end of the lever rests in quicksand ,force cannot be meaningfully applied to the load .

[Edmund Cramp]

Thanks for this Gerrard, I've always worked with data collection so that clinicians and researchers can do the analysis but it's very interesting now, having seen this topic, to walk around and monitor the effects (just how I feel, no devices involved) of using my toes and then, keeping them up so that my walking is heel to metatarsals not toes, while feeling how my body is manipulated. It's been many years but I remember working with someone at least 30 years ago who was doing fine-wire recordings from foot muscles to try and determine what problems his patient was having - my task back then was simply to help him be confident that the movement, force plate, and EMG data was accurate - it was.
And now, years later I still find it very interesting to just walk myself every morning and feel how my thoughts about things like this manipulate my walking. It was very helpful back in my early days of gait analysis when I was told, "Look at these graphs, now walk yourself to move in exactly the way these graphs are documenting" - doing that was very educational!

[Gerrard Farrell]

Hi Edmund

Thanks for taking an interest in this, I am afraid that when it comes to the foot several key mechanical aspects have been misunderstood and these misunderstandings are preventing us from finding solutions to conditions like plantar fasciitis.

The idea that the intrinsic foot muscles that span the arch from the heel to the toes, act to support the medial longitudinal arch began to gather steam after Luke Kelly's paper in 2014.

He and his fellow researchers found that if you electrically activate the abductor hallucis muscle then a loaded foot will shorten and the navicular bone will rise indicating increased arch height. This was interpreted by Kelly, and subsequently by many others, as evidence that the intrinsic foot muscles support the arch. I don't think this is an accurate interpretation of the experimental results and I believe the error is an important one . Here is why .

The abductor hallucis muscle has a number of sites of origin and attaches to the base of the proximal pharynx of the big toe or to the sesamoid apparatus but it does not attach to the metatarsal head .Thus, it's primary function is to plantarflex and abduct the hallux .

When a foot is loaded, as it was in Kelly's experiment, the foot becomes flattened by the load, and the plantar ligaments and fascia are themselves put under load . If the abductor hallucis is activated this causes the toe to plantarflex and it pushes down into the ground . Thus the load on the foot is now being shared by the planta fascia, plantar ligaments and the ABDH as it presses the great toe down . Thus it is more accurate to say that the ABDH helps spread the load on the foot rather than it supports the arch. If load is being applied through the toe then the plantar fascia and plantar ligaments will be under less compressive load and the arch height will rise.

I get the impression that the Kelly paper was heavily influenced by the short foot exercise popularized by Janda and this has caused confusion . If you look at the schematic drawing below Kelly and his associate researchers have a proximal phalanx whose base has become dorsiflexed on the 1st metatarsal head by contraction of the abductor hallucis and this is not what happens.

2014 KELLY.jpg
In any event, if the intrinsic foot muscles are to contribute to load sharing across the foot during standing working tasks the toes must have something under them on which the can press, not a yielding toe spring.

[Gerrard Farrell]

The intrinsic and extrinsic toe flexors to do not directly act to pull the met heads towards the heel as Janda said . In fact the Janda short foot exercise is a bit of an "academic tar pit" which has led many good researchers astray.

If the Janda short foot exercise is performed without downward pressure on the toes then the intrinsics are NOT engaged but instead the tibialis posterior ,tibialis anterior and peroneals are responsible for arch movement .

Here is a youtube video which illustrates the point . Note that the met heads are being pulled towards the heel ,lifting the arch, but the toes are free to wiggle . Janda was wrong .

https://youtu.be/iy1Qxt2mnsE

[Gerrard Farrell]

So here is a request for some information . If you stand in single leg stance, does being barefoot or in modern footwear ( trainers ets ) change where the center of pressure is located under the foot ?

To answer this question you might need a couple of consenting volunteers, a force plate, and research know- how .The answer might help many thousands of factory workers and the like who suffer from chronic foot pain.

I suspect that modern shoes mean the center of pressure is located further from the heel in the shod condition and more proximally in the barefoot condition and that this will impact the long term health of the plantar fascia. However, there is no proof of this that I am aware of, and nobody seems to have looked .

So if anyone out there has access to a force plate ........

[Edmund Cramp]

I think that this has the potential for very interesting research with a wide range of subjects, another possible factor would be the degree of exercise that the volunteers are performing every day, something that I think could affect how the subjects walk over, or stand on, the force plate. I wonder if we would see different results from someone who runs every day, versus someone who spends an hour on an elliptical workout every day - both seen by subjects just as “exercise” but with significantly different foot balance and leg movement exercise.

The perfect environment for this study would be a 3D gait lab with force plates so that you can collect both the force and moments together with the subjects stance - it would be a very interesting study with data collected from a range of people - subjects wearing different types of shoes, while others comfortably bare-footed. Another factor would be the subjects age, I can remember walking much better 60 years ago (LOL).

I wonder if this study could receive support and funding from a few shoe companies to support a significantly large range of subjects?

[Gerrard Farrell]

Hi Edmund,

Thanks for taking an interest .

In my previous post I wrote -" I suspect that modern shoes mean the center of pressure is located further from the heel in the shod condition and more proximally in the barefoot condition and that this will impact the long term health of the plantar fascia. However, there is no proof of this that I am aware of, and nobody seems to have looked ."

I did not make it clear that I was taking about the COP only with regard to standing and not waking /running etc . The work Kelly did in 2014 related only to a set up that tried to mimic single leg stance.

Plantar fasciitis is a common complaint for workers standing on assembly lines all day or for surgeons in theatre. When we stand for a prolonged period we tend to put our weight on one leg for a time and then transfer it across to the other leg. Thus standing on an assembly line will often see worker in something approaching a single leg stance in which the toes flexors are activated . My theory is that shoes with toe springs reduce toe flexor activity/effectiveness and so the COG will be more distal in individuals in modern shoes . This will tend to load the plantar fascia .

Moving to a shoe with no toe spring might well allow the toe flexors to work more effectively giving a more proximal COG and less load on the PF . Over time shoes without toe springs may be better for standing occupations with regard to PF health .

[Edmund Cramp]

Thanks Gerrard, There's a study about this available here - https://pubmed.ncbi.nlm.nih.gov/32943665/ ... it looks very helpful, I've found your postings to be very interesting, making me think and play with my foot contacts during my daily walks. Having read many of Dan Lieberman's books about our evolution and its' effects on us now, always makes my daily walk observations interesting, watching and feeling my feet contact and stance changes on the pavement and the grass.
I had made the comment that doing a study in a clinical gait lab would be helpful but thinking about it while walking this morning has made me think that the actually "testing" environment can have a significant effect on what we see - a gait lab is a nice quiet environment usually but I remembered setting up a lab about 20 years ago and the surgeon doing a test data collection by running through the lab - so fast that he ran into the wall at the end of the data collection volume and his hand made a hole in the wall! Luckily only some bruising but his running resulted in totally different data then we were expecting to see. We repeated a study with a PT mimicking a CP patient and everyone was confident with the system performance once she had walked normally the second time.

[Gerrard Farrell]

Whilst toe springs likely inhibit toe flexor function and this may be important for COP location during standing tasks, the stiff sole of many modern shoes may also be a contributor to toe flexor weakness. If you bend a modern running shoe in the region of the MTPJ it will spring back into position with considerable force . The toes need not develop force if the shoe is doing it for them.

Some shoes might even be seen as exoskeletons for the foot.