It seems to me that if you want to reduce load on the PF by strengthening the intrinsic and extrinsic toe flexor muscles you must also ensure that the patient is generally wearing shoes that have no or very little toe spring.
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Toe springs negate the positive work that the toe flexor muscles can do as a standing subject shifts weight from one foot to the other during standing tasks.
Modern shoe design weakens the toe flexor muscles indicating that these are used less in the shod condition ( what else could it mean ?) . This means that something else must be taking the load during standing tasks and that something is probably the plantar fascia.
Strengthening the foot's musculature is probably meaningless unless that musculature can function properly and that means altering shoes design . Not cushioning ,not medial arch support but definitely toe springs.
Sure, toe springs may feel more comfortable to walk with, but if they contribute to PF then that should be considered when treating the condition.
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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 the 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.
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.
Last edited: Dec 10, 2022 -
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 .
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The reason that the toe will try to plantar flex is not the downward pull of the attachment from the sesamoids on to the base of the proximal phalanx, but the force couple created by proximal pull and the forward push from the metatarsal head.
In a shoe with a rocker tip (similar to toe spring) the center of pressure under the foot stays proximal longer and this reduces the bending moment on the foot. So the muscle can redistribute internal loads within the tension structures even with a flexible rocker tip and the rocker tip can reduce the external load. -
Sure, the abductor hallucis will apply force to the head of the first met head via the base of the proximal phalanx ( not sure that my typo was that funny but whatever floats your boat ) and this will tend to raise the arch. However, the sesamoid apparatus will minimis this .That is, the sesamoids act to increase flexion forces and reduce "arch raising" forces.
You could say that the anatomy of the abductor hallucis and associated sesamoids is specifically designed to reduce the arch shortening properties of the muscle and increase its ability to generate flexion forces around the MTPJ .
In any event you surely can't run an experiment on the effects that the abductor hallucis has on the arch whist ignoring the forces generated under the toes.
Did you look at the video Eric ? How do you explain what we see ? -
Not withstanding the above, I believe it is more accurate to say that Kelly et al 2014 shows that the intrinsic foot muscles help to share load across the whole foot with increasing postural demand . Thus the intrinsic that span the arch don't so much support the medial longitudinal arch but take load away from it and spread it across a longer "whole foot" medial arch. ( The extrinsic toe flexors will add greatly to this effect).
I believe it is highly likely that toe springs impede this intrinsic load spreading mechanism and for workers on an assembly line for example, this means that when they move their body weight from one foot to another during standing ,the plantar fascia is subjected to increased load .
Thus a treatment that clinicians might consider for PF associated with standing all day might be toe flexor strengthening/activation exercises and footwear with no toe spring . Cushioning and arch support might help also.
The toe flexors fulfill a function in the foot that nothing else in the foot can help with . They have a critical and unique role in foot biomechanics. This is true of the intrinsic and extrinsic toe muscles . -
Eric , below is a diagram of the foot . Look at the figure on the right hand side .
The system can be viewed as a wheel barrow type set up with the calcaneus the wheel , the tibia/fibia the load and the rest of the foot the long handles of the barrow .
When you lift the handles of a wheelbarrow you shift the COG closer to the pivot point or wheel . So it is with the foot .
If you lift the met heads by planter flexing the toes then you move the COG more towards the pivot point represented by the calcaneus . This reduces the load on the arch of the foot and allows it to be less compressed and lift.
This is what Kelly et al 2014 demonstrates . Does this make sense to you ?
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In what situation are you talking about the muscles inserted into the toes are lifting the metatarsal heads off of the ground?
The center of pressure, of ground reaction force, moves forward with contraction of the gastroc and soleus muscles. As the center of pressure moves forward tension in the fascia increases. -
For example if the QP is stimulated in a foot under load then Kelly found in his experiments -
"Our second experiment demonstrated that electrically induced contractions of individual intrinsic foot muscles (AH, FDB and QP), over and beyond their natural activity, can attenuate and even reverse LA arch deformation."
What is happening is that contraction of QP pushes the toes into the ground causing the COG or center of pressure to move towards the calcaneus resulting in less stress on the PF . You could say that the knee and ankle joints become more "stacked" ,or more pressure through the heel whilst retaining balance.
I am speculating that modern shoes ,which produce weaker feet , see less active intrinsic activity during single leg stance than the unshod condition, meaning a more distally placed COP and greater day long load in the PF . Further, it is most likely the toe spring element of modern shoes that causes the problem .
This thread relates to standing and not gait . -
If you look at the foot as beam, or tied arch, you can understand how contraction of the intrinsic muscles could decrease strain in the plantar fascia. When a beam is supported at its ends and there is a weight in the middle, an external bending moment on the beam is created. To resist this bending there is tension on the bottom and compression at the top. In the foot there is redundancy in which structures can have tension to resist bending moment. For a given load, if you increase tension in one structure (muscles), you don't need as much tension in another structure (plantar fascia). This is a plausible method by which muscle strengthening could help plantar fasciitis.
You can't have a thread that talks about plantar fasciitis and only talks about standing and not gait. Hicks showed long ago that with increase in Achilles tendon tension, there is an increase in plantar fascial tension. If plantar fasciitis is caused by increased tension, it probably happens at some other time than standing in static stance.
With increased Achilles tension, there is increased bending moment on the foot. Increased bending moment on the foot will increase tension in the plantar fascia. The further anterior the center of pressure, the greater the bending moment on the foot. There are studies that show that a rocker tip shoe slows the progression of the center of pressure. A rocker tip shoe will have toe spring. Not all shoes with toe spring have a rocker tip. There is a plausible explanation of why a shoe with a toe spring would be good for plantar fasciitis. -
Kelly found that when the intrinsic foot muscles that span the foot contract the center of pressure shifts posteriorly not anteriorly.
I find that if I stand and contract my toe flexors my COG moves posteriorly as done the line of gravity through my foot as does the COP since I can feel greater pressure under my heel .
If you try to press your toes down by leaning forwards you would have a COP that moves anteriorly but that is not what I am discussing.
Do you think Kelly would have gotten the same results in 2014 if the feet being tested rested on a board that extended from heel to the ball of the foot only and the toes where free to plantarflex with no resistance? -
Last edited: Dec 22, 2022 -
Luke A Kelly 1, Andrew G Cresswell, Sebastien Racinais, Rodney Whiteley, Glen Lichtwark
Affiliations expand
- PMID: 24478287
- PMCID: PMC3928948
- DOI: 10.1098/rsif.2013.1188
- PMID: 24478287
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There has to be equilibrium about the STJ and ankle joints with changes in body position. When you lean forward, your center of mass moves forward relative to the ankle joint. That means gravity acting on the center of mass and ground reaction force through the ankle joint will tend to rotate the body forward unless something stops it. Contraction of the gastroc and soleus muscles will stop that forward rotation. When you lean forward, you subconsciously contract muscles to maintain balance.
Abductor hallucis will shorten when the toe is plantarflexed and when the arch is raised. One question is there is still significant force generated in the muscle belly if both of those motions have occurred. If the muscle is strong enough to bend a shoe with a toe spring, then there will still be tension in the muscle. If the shoe is too stiff for the toe to bend the shoe, the situation would be similar to when the toe is on the ground. I still think the rationale you gave on the avoidance of toe spring when treating plantar fasciitis is wrong.
Another question is whether the amount of change in the tension in the plantar fascia from contraction of the intrinsic muscles is big enough to matter. What did that paper you mentioned on arena a ways back say. The intrinsic muscles only contribute about 3 percent. There are other factors beyond the intrinsic muscles that affect tension in the plantar fascia. -
In general, toe flexor activity may well allow a balance position in single leg stance which sees more weight on the heel thus reducing stain on the foot. IMO this requires urgent investigation.
Do toe springs encourage reduce toe flexor contributions during standing /gait? Research strongly suggests that some aspect of modern footwear does . Which aspect(s) do you think it is? -
Hi, im facing extreme pain (mostly when i go to bed to sleep) for the last 15 days in both my feet and legs, the pain is mostly 80% on the sole of the foot starting in the smaller finger and ending in the heel and 20% starting below the calf going to the foot. Initially i thought it was cold feet but nothing worked, not sock, blankets, nothing. Today i think or feel that is a nerve or a tendon, its like a burning sensation. At the beginning the doctors thought several things like thyroid and they did a lot of test, everything its normal, the only pending test is a electromyographic study. Im starting to think its plantar fascitis, it started 15 days ago when I did a huge effort for 15 continuous days (a work situation), the pain started 1 hour after I woke up but I did had to work for 12 more hours, more than 20.000 steps more daily after the pain starts, I did this crazy effort for 15 days. Can you give me and advice? Help me to figure it out what can it be? How to solve it?
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Eric ,
If modern shoes mean less activity in the toe flexor muscles, what does that mean for the overall roles of the flexor hallucis longus and flexor hallucis longus and how would that impact strain within the Achilles tendon?
Toe flexor strength increases by 57% in more minimal shoes after 6 months of use in everyday activities and this presumably means a lot more input from the long toe flexors during gait which would assist the Achilles in plantarflexing the foot.
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Plantar Fasciitis is a symptom, not a primary aetiology. That is why addressing PF with connective tissue stretching exercises can be very frustrating. Yes, stretching these tissues can/will attenuate your symptoms, but the symptoms will return with a vengeance when/if you stop you stretching routine, even for just a day.
A better approach would be to isolate the primary aetiology of PF and treat that pathology directly. Doing so, the symptoms of PF abate without stretching several times a day.
Two of the most common causes of PF are:
- RFS (Rothbarts Foot Structure)
- PreClinical Clubfoot Deformity
Hope this helps. -
It is very unlikely that the decrease in tension is from shifting the location of the center of pressure. The loads on the plantar fascia are much higher in walking or running compared to static stance. In walking and running the motions that are required require large amounts of force in the Achilles tendon. With ankle plantar flexion and heel lift the center of pressure is shifted anterior. This would negate any affect on center of pressure changes from the intrinsic muscles.
If pathology of the plantar fascia is caused by increase tension, then you should not be looking at static stance.
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Only muscles that cross the ankle joint can create a moment at the ankle joint. A muscles ability to assist in ankle plantar flexion is dependent on the lever arm of the muscle at the ankle joint. The muscles of the Achilles tendon have a very large lever arm and are much stronger than the other flexors. Flexor hallucis longus has a some lever arm at the ankle, less than the Achilles and it is a much weaker muscle. Flexor digitorum longus has essentially no lever arm at the ankle joint. Flexor hallucis brevis does not cross the ankle joint and cannot aid in ankle plantar flexion. -
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Another finding that is relevant here from the muscle activation studies is that with a half body weight load the intrinsic muscles were not contracting. Just because a muscle is stronger does not mean that it is active. -
I enjoy our conversations Eric and apparently so do others . However, my purpose is not persuade you or Brian Rothbart that foot strengthening is a good idea and it's certainly not to directly sell foot exercise devices. My targets are the researchers. -
In patients with Hip Drive Pronation, these 3 muscles demonstrate remarkable resiliency in preventing ILA collapse. -
Gravity drive pronation , Hip drive pronation
Terms not used in mainstream biomechanics.
A growing body of search indicates that foot strengthening may be an effective treatment for flat feet. What exercises do you prescribe?
Placing a 3mm wedge under the 1st MTPJ will have a mechanical effect. It makes sense to me that mechanical ( anatomical) abnormalities e.g. RF as you call it , might benefit from mechanical interventions such as your orthotics, and sensory deficits , e.g. neuropathy ,might benefit from proprioceptive interventions such as vibrating insoles.
If RF benefits from proprioceptive intervention then would vibrating insoles not be a better solution than your orthotics ? -
Any theory on why intrinsic muscles are used less would have to account for why individuals choose to use them less. A shoe cannot prevent the use of the muscles. You can still use the muscles even if the foot is "immobilized" in a shoe. This would be true especially true, in high load situations like running or jumping where the intrinsic muscles could add to foot rigidity and reduce strain on passive structures. -
I later termed the abnormal pronation resulting from the structural deformation observed in RFS - Gravity Drive Pronation (2002).
Regarding Vibrating Insoles, I have had no clinical experience using this type of insole, to comment.
- Inman Verne. The joints of the ankle. II. Biomechanics of the subtalar joint. Baltimore: Williams & Wilkins, 1976.
- Rothbart BA, 2002. Medial Column Foot Systems: An Innovative Tool for Improving Posture. Journal of Bodywork and Movement Therapies (6)1:37-46
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Brian, please read what's written. "Terms" does not mean "concepts". Some of the concepts and conditions you have coined phrases for were know of well before you you qualified, DPM.
Mechanical problems teach towards mechanical solutions. -
Kindly refresh my memory: what other concepts or conditions I coined phrases for, that were known "well before I qualified, DPM"
My research was discovering the link between gravity and pronation/supination of the STJ and I coined that term Gravity Drive Pronation. Two of the most common foot deformations that function in Gravity Drive Pronation are RFS and PCFD -
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Also, Brian, you may be misquoting Inman. My recollection was that Inman described the motion and did not mention causation. Can you provide the quote from Inman where he talks about causation of motion? Or did you just make that up?
Looking at post #27 one could conclude that hip drive and gravity drive pronation are not terms commonly used in biomechanics.
Someone using the term gravity drive pronation should be able to explain how gravity creates the moments that cause the motion. We've been through this before on the thread where Brian advocated for not using moments when talking about motion. The science of the study of motion uses moments. -
May I suggest you read these two papers and then ask any remaining questions (if any) or any clarification you require.
- Rothbart BA, Esterbrook L, 1988. Excessive Pronation: A Major Biomechanical Determinant in the Development of Chondromalacia and Pelvic Lists. Journal Manipulative Physiologic Therapeutics 11(5): 373-379.
- Rothbart BA, 2002. Medial Column Foot Systems: An Innovative Tool for Improving Posture. Journal of Bodywork and Movement Therapies (6)1:37-46
Hip Drive Pronation is a term I coined to describe Verne Inman's research. -
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Several years later, Inman (1981) linked the transverse plane rotations of the pelvic girdle to the internal and external shank rotations.
In 1988 combining my research on foot kinetics and drawing on Inman’s earlier research (1976, 1981), I linked pelvic girdle oscillations to STJ pronation and supination. In 2008 I coined the term Hip Directed (Drive) Pronation when referring to this link.
- Inman VT 1976. The Joints of the Ankle. Chapter 11 Biomechanics of the Subtalar Joint, Pg.66, Figure 11.14. Williams and Wilkins Baltimore
- Inman VT 1981. Human Walking. 1. Introduction. Baltimore: Williams and Wilkins.
- Rothbart BA 2008. Vertical Facial Dimensions Linked to Abnormal Foot Motion. Journal American Podiatric Medical Association, 98(3):01-08, May.
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I discussed this very point in a paper I published in 2011. Take a read. If you have any questions or need clarification, start a new thread and we can discuss this in detail.
- Rothbart BA 2011. Twisting Foot and Musculoskeletal Pain: Root's Biomechanical Model vs Rothbarts Neurophysiological Model. Positive Health, Issue 186, September.
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Brian is still stuck in 1976. There is a reason that hip drive pronation is not a commonly used term in biomechanics. See the 11+ year old discussion.Last edited: Jan 11, 2023 -
Out of interest Brian, what aspect of the modern shoe do you think causes disuse atrophy of the toe flexor muscles?
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Research Interest Score 161.5 (which is higher than 73% of ResearchGate members)
Citations 212
h-index 7
And over 18,000 reads!
Hardly indicative of someone stuck in 1976.
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