Intrinsic foot muscles contribute to elastic energy storage and return in the human foot.
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Kelly LA, Farris DJ, Cresswell AG, Lichtwark GA
J Appl Physiol (1985). 2018 Nov 21
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The energetic function of the human foot and its muscles during accelerations and decelerations
Ross E. Smith , Glen A. Lichtwark, Luke A. Kelly
J Exp Biol (2021) 224 (13): jeb242263.
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Smith et al, above, is about center of mass work whilst jumping up and down .
However, the intrinsics may contribute more to center of mass movement when leaning forwards to accelerate .
Quote
"Therefore, the small size of intrinsic muscles appears to limit their capacity to contribute to center of mass work." , Yes but only within the limits of jumping up and down .
Using a nerve block then testing the effects on flat out horizontal acceleration is probably not a good idea . At all . -
From what I could see of the study design from reading the abstract, I would believe the 3% contribution of the intrinsic muscles for moving the center of mass. -
The majority of the IFM are toe flexors . If you lean forwards and start to accelerate in a sprint type action, the toes will move through a greater range of motion than jumping up and down, giving the intrinsic more opportunity to apply force and move the COM .
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Toes are dorsiflexed about twice as much during horizontal jumping ( a lot like sprinting low of a standing start) as they are during vertical jumping .
Goldmann et al found toe flexor strengthening improved horizontal jump but not vertical .
I haven't seen the whole Smith paper but likely the toe flexors of the participants were hopelessly weak compared to individuals used to moving about unshod . They might well have toe flexors of only 50% of "natural" levels .
In unshod individuals the figure of 3% contribution might easily be higher . -
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The tissues, from the MTPJ to the tip of the toes, is a substantial part of the foot and is powered by the intrinsics and extrinsics ,a substantial combined muscle mass . If you are leaping forwards, the COM passes over the toes and the dorsiflxed toes are in a position to contribute energy ,through plantarflexion , to the COM in its direction of travel .
Running along at a steady rate and sprinting from a standing start, probably make very different demands the toe flexors .
With the advantage of hindsight, it is difficult to study any body system that is woefully understrength, due to a lifetime of splint usage .
It is perfectly possibly that, over the course of a career, a foot health care professional will see patients 90% + of whom have feet only half as strong as their natural levels . Could help explain a few pathologies .Last edited: Aug 11, 2021 -
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Standing long jump used to be an Olympic event .It anecdotal, but there seems to be a bit of snappy plantar flexion going on here .
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Body positions are very different when you are coming out of the blocks and over the last 40m in a 100m race .
I don't think Stefanyshin and Nigg looked at the first few strides during acceleration or the standing long jump . In these two instances the toes are substantially plantarflexed .
Also the subjects studied by Stefanyshin and Nigg where likely habitually shod and may have had plantar flexor strength of only half the "natural" unshod norm .
If you watch the video in post #11 you can see marked dorsiflexion and rapid plantarflexion . -
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And the words of the prophet were written on the subway walls and echoed with the sound of salesmen.. Don’t know why you still bother, Eric.
Persistent spamming killed this forum. RIP Podiatry Arena -
"Your last word above, did you mean dorsiflexed?" Yes ,typo
"Muscles are weak from lack of use. The runners in those studies were trained runners. Are you saying that they were not using their intrinsic muscles when they were training in shoes?"
I am saying that shod runners seem to use their intrinsic foot muscles less than habitually unshod runners .
"I see shoes on the person in that video. How can you tell if there is plantar flexion of the toes in the shoes?" I thought they were socks ,but whatever the subject is wearing, it conforms pretty snuggly to the foot .
Spamming can take a number of forms . For example continually popping up with comments about the site being dead . -
So Smith et al concluded in part that
"Also, while the intrinsic muscles can modulate the energetic capacity of the foot, their removal accounted for only a 3% decrement in total center of mass work. Therefore, the small size of intrinsic muscles appears to limit their capacity to contribute to center of mass work. However, their role in contributing to ankle work capacity is likely important for the energetics of movement"
I have not seen the full paper but, by jumping and landing, I assume they mean vertical jumping . During most of the acceleration phase of the vertical jump the foot is flat on the ground and much of the force goes through the heel . Likely foot stiffness is not as important for this type of activity as it is for others .
For example, I have linked to a video ,below, that shows the early acceleration phase of a sprint . The heel does not touch the ground and foot stiffness will clearly be important here in generating GRF .
Recently, Welte et al demonstrated that with the heel up and the toes dorsiflexed the intrinsics contribute more to foot stiffness than the windlass mechanism .
I would expect that the intrinsic have a greater role to play in activities where the heel is less involved in generating GRF .
Another aspect of Smith et al which is not mentioned in the abstract is the possibility of the extrinsics doing some of the work of the intrinsics in their "absence" . The 3% might simply be "that which cannot be replaced by other systems "
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In the post above I said
"Welte et al demonstrated that with the heel up and the toes dorsiflexed the intrinsics contribute more to foot stiffness than the windlass mechanism ."
I should have said Farris et al 2020 https://doi.org/10.1098/rsif.2020.0208
From their paper
5. Conclusion
In summary, our results show that maintaining tension across the plantar aspect of the foot involves active muscular contraction of ankle plantar flexors and plantar intrinsic muscles. Therefore, the passive windlass mechanism is not the foot's source of rigidity for push-off against the ground during gait. In fact, within the foot, increasing push-off for changes in gait mechanics relies primarily on foot muscles and not winding of the plantar aponeurosis via the windlass mechanism.
Also , and controversially
"We conclude that active muscular contraction, not the passive windlass mechanism, is the foot's primary source of rigidity for push-off against the ground during bipedal walking."
( Note that they are not saying the PF does not contributed to foot stiffness, just that the windlass adds no additional stiffness .This aspect seems to have been misunderstood by some ) -
Having read Smith et al 2021 , jumps and landings were carried out on a single foot . This would mean that the majority of the COM would be done "heel down " with the foot flat on the floor in a mid stance type position .
During gait, mid stance is not associated with high levels of activity in the intrinsics , with these muscles coming more into play as the heel lifts .
However, in their experiments ,the authors found that the intrinsics are important both for the generation of foot power and ankle power regardless of the fact that the IFM are less involved in the experimental tasks than they would be during the first few steps of a sprint or a cutting maneuver (heel up ) .
It is surprising that the intrinsics make such a significant direct and indirect contribution to COM work in this study, especially when you considered that habitually shod subjects probably have very weak toe flexors/IFM compared to "natural " levels . -
The energetic function of the human foot and its muscles during accelerations and decelerations
Ross E. Smith , Glen A. Lichtwark, Luke A. Kelly
J Exp Biol (2021) 224 (13): jeb242263.
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From Smith et al, above -
" Also, while the intrinsic muscles can modulate the energetic capacity of the foot, their removal accounted for only a 3% decrement in total center of mass work. "
However, what Smith and his colleagues would not have been aware of at the time of writing up this research, is that the feet of their subjects likely only had toe flexor strength of between 50-60% of natural, unshod levels . This is important because this deficit can be reversed . -
Flexor digitorum brevis utilises elastic strain energy to contribute to both work generation and energy absorption at the foot
Ross E. Smith, Glen A. Lichtwark, Luke A. Kelly
J Exp Biol jeb.243792.
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When strengthening a muscle/tendon unit my understanding is that you would use resistance exercises over a period of a few months. So if you want to improve the efficiency of the way in which the flexor digitorum brevis contributes to energy absorption, or storage and return, during gait, this seems like the way to go.
I feel it is important to note that the study group in R Smith et al are probably average, habitually shod people with toe flexors a lot weaker than they naturally should be . Could be a lot of scope for improvement ! -
Further, how do Janda’s theories re: muscle length-tension relationships fit with this? As I recall, Janda suggested it was the muscle length that was key and not the strength, since strengthening exercises only elevate the length-tension curves upward and do not lead to optimal force production at the optimal point within range?Last edited: Mar 29, 2022 -
My understanding is that thicker tendons are stiffer and can handle more work/store and release more energy, than
thinner tendons .
It may be that strengthening the FDB's active contractile component does less for the muscle/tendon units ability to contribute towards gait than changing tendon thickness/stiffness .
I also understanding that you can thicken muscle tendons by resistance exercises over time, but that it takes months to get an effect rather than a few weeks ( neural changes ) or 2 weeks plus ( contractile component changes ) .
In short, and in the present context, I see strengthening exercises as a way of increasing tendon stiffness and strength once gained as a way of retaining that stiffness and higher level of function of the whole.
Most IFM research lasts less than 6-7 weeks and perhaps 3-4 months would be a better time frame to allow changes to occur in the tendons of these muscles, when studying some of the functions of the IFMs ( those discussed in the paper). -
2nd moment of area, for similar structures, obvs.
Your point seems to be that shoes with a toe-spring hold the muscles in a lengthened position and thus the muscles should become long and weak, adding sarcomeres in series. You may want to remind me of the references for shoes making the intrinsics weak since I recall reviewing a paper which compared barefoot to shod populations but didn’t take into account the considerable difference in activity levels between populations. Both myself and the other reviewer rejected that paper, but it was later published in another journal… anyway if the muscle is long and weak according to Janda, the length tension curve will move to the right as such strengthening exercises will only move the curve upwards and not back to the left in the length-tension curve. Thus, while the muscle may be stronger, it is still not developing optimal force at the right place nor time within the RoM. -
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Go back and look at what I wrote because I was editing it when you replied.-
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No , I've never said anything like that at all. In fact I have no idea what you mean .
Re toe springs, all my shoes have them, even my waders . -
Scientific Reports volume 11, Article number: 18648 (2021) Cite this article
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The human foot is uniquely adapted to bipedal locomotion and has a deformable arch of variable stiffness. Intrinsic foot muscles regulate arch deformation, making them important for foot function. In this study we explore the hypothesis that normal daily activity in minimal footwear, which provides little or no support, increases foot muscle strength. Western adults wore minimal footwear for a six-month period (the “intervention” group). Foot strength, i.e., maximum isometric plantarflexion strength at the metatarsophalangeal joints, and foot biometrics were measured before and after the intervention. An additional group was investigated to add further insight on the long-term effects of footwear, consisting of Western adults with an average 2.5 years of experience in minimal footwear (the “experienced” group). This study shows that foot strength increases by, on average, 57.4% (p < 0.001) after six months of daily activity in minimal footwear. The experienced group had similar foot strength as the post intervention group, suggesting that six months of regular minimal footwear use is sufficient to gain full strength, which may aid healthy balance and gait. -
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I think they looked at 2 groups . Group 1 were experienced with minimal footwear and group 2 were not . Group 1 had two flexor strength 60% higher than than group 2, the folk who did not use minimal footwear.
Then they took the group 2 people and gave them minimal shoes to use for daily tasks and 6 months later their toe flexor strength was the same as the group 1 people ,that is, it had improved by almost 60% .
Curtis et al used a similar format to a study I read a few years ago about female Japanese marathon runners with shin splints. Researchers looking at this problem compared toe flexor strength in the runners compared to non athletic nurses and found the nurses had stronger foot muscles .
The researchers then gave the runners a course of strengthening exercises to do and the shin splints got better .
How are you getting on with the toe pro?Last edited: Mar 31, 2022 -
re: Toe pro, I’ve found most patients are a bit put off by the price when I point out they can achieve similar with a rolled up towel. -
I find the paper convincing esp with such strong results .
Re Toe Pro . When you say "achieved similar" what do you mean? What is achieved? -
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You advocate strengthening exercises as part of the treatment plan for plantar heel pain?
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