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Intrinsic foot muscles contribute to elastic energy storage and return in the human foot

Discussion in 'Biomechanics, Sports and Foot orthoses' started by NewsBot, Nov 23, 2018.

  1. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
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    Intrinsic foot muscles contribute to elastic energy storage and return in the human foot.
    Kelly LA, Farris DJ, Cresswell AG, Lichtwark GA
    J Appl Physiol (1985). 2018 Nov 21
     
  2. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
    1
    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.
     
  3. scotfoot

    scotfoot Well-Known Member

    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 .
     
  4. efuller

    efuller MVP

    The ankle joint will contribute to center of mass movement both vertically and horizontally. Increasing the rigidity of the foot will increase the movement. There is just different resistance vertically versus horizontally. The horizontal resistance is the inertia of the mass of the body. Vertically, upward movement is resisted by the inertia of body mass plus the force of gravity acting on the body.

    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.
     
  5. scotfoot

    scotfoot Well-Known Member

    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 .
     
  6. efuller

    efuller MVP

    Why do you think the toes will move through a greater range of motion? How many more degrees would you get and is this important for changing 3% of the push?
     
  7. scotfoot

    scotfoot Well-Known Member

    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 .
     
  8. efuller

    efuller MVP

    Just because the toes are more dorsiflexed at the start does not mean that they will plantar flex. I don't recall the author, but there was a paper looking at power output of the toes and it mentioned very little power and they saw more negative power than positive in running. Positive power, or addition of energy, occurs when the motion is in the same direction as the moment. Power is negative when the moment, or torque is in the opposite direction of the motion.
     
  9. scotfoot

    scotfoot Well-Known Member

    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
  10. Here Eric https://pubmed.ncbi.nlm.nih.gov/9456374/
     
  11. scotfoot

    scotfoot Well-Known Member

    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 .

     
  12. efuller

    efuller MVP

    Theoretically possible does not necessarily mean that it happens. As the Stefanyshin and Nigg (thanks Simon) paper shows the toes don't actually plantar flex. The moment calculated in the inverse dynamic experiment shows that there is tension in the intrinsics and plantar tension contributes to the rigidity of the foot. So, there is a small contribution.


    Yes, the different demand is the amount of resistance. Jumping up and down the resistance to movement is inertia plus the downward pull of gravity. From a standing start, or a crouched start, the resistance is inertia of the body. Steady state running the resistance is wind resistance. However, both from a start and during steady state, there has to be some upward acceleration during stance because there will be downward acceleration during double float (both feet off of ground).
     
  13. scotfoot

    scotfoot Well-Known Member

    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 .
     
  14. efuller

    efuller MVP

    In a quick look at pictures of runners in starting blocks, they all seem to have their toe on the angled block, so the toes are not dorisiflexed very much in the block. Your last word above, did you mean dorsiflexed? If you meant plantar flexed, what evidence do you have that they actually planarflex against substantial resistance?


    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 see shoes on the person in that video. How can you tell if there is plantar flexion of the toes in the shoes?
     
  15. 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
     
  16. scotfoot

    scotfoot Well-Known Member

    "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 .
     
  17. scotfoot

    scotfoot Well-Known Member

    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 "

     
  18. scotfoot

    scotfoot Well-Known Member

    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 )
     
  19. scotfoot

    scotfoot Well-Known Member

    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 .
     
  20. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
    1
    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.
     
  21. scotfoot

    scotfoot Well-Known Member

    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 .
     
  22. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
    1
    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.
     
  23. scotfoot

    scotfoot Well-Known Member

    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 !
     
  24. What is the relationship between muscle “strength” and energy storage/ return? Since the area beneath the stress/ strain curve is the energy stored, how do strengthening exercises modify the stress/ strain curve?

    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
  25. scotfoot

    scotfoot Well-Known Member

    Smith et al seem to be focusing on the tendons of the FDB as the part of the muscle that does much of the useful work of the whole . I read the paper as the tendons stretch and store energy that is later returned in gait or else dissipated depending on energetic requirements, and the contractile, fascicle containing component of the muscle or muscle belly ,provides governance .

    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).
     
  26. Steel bars are stiffer than elastic bands of the same cross-sectional area, but which would you choose to store and return the elastic strain energy? Is there an optimal stiffness? Can a muscle/ tendon unit be too strong?

    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.
     
  27. scotfoot

    scotfoot Well-Known Member

    I am not sure I understand your point but I would prefer to have a foot as close to what nature intended as possible.
     
  28. The appeal to nature fallacy. But the foot doesn’t function in natural environments any more. Moreover, go walk barefoot in the wild and you’ll soon see why our ancestors invented shoes.

    Go back and look at what I wrote because I was editing it when you replied.
     
  29. scotfoot

    scotfoot Well-Known Member


    No , I've never said anything like that at all. In fact I have no idea what you mean .

    I'm not advocating going barefoot at all . Never have done. Keep the feet strong and wear supportive shoes, that's what I do .
    Re toe springs, all my shoes have them, even my waders .
     
  30. scotfoot

    scotfoot Well-Known Member

    Daily activity in minimal footwear increases foot strength

    Scientific Reports volume 11, Article number: 18648 (2021) Cite this article
    Abstract

    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.
     
  31. was there a control group that completed the same daily activity in non-minimalist shoes?
     
  32. scotfoot

    scotfoot Well-Known Member

    p< 0.001
     
  33. Just I couldn’t see any activity level for the control group in table 5?
     
  34. scotfoot

    scotfoot Well-Known Member

    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
  35. As I thought, so we can’t be sure that activity levels didn’t increase as a result of the subjects being involved in the trial.

    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.
     
  36. scotfoot

    scotfoot Well-Known Member

    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?
     
  37. The ability to perform the exercise as described by Rathleff as an adjunct to other therapies in the management of plantar heel pain
     
  38. scotfoot

    scotfoot Well-Known Member

    You advocate strengthening exercises as part of the treatment plan for plantar heel pain?
     
  39. Yep, and involved in a study…. Watch this space
     
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  40. scotfoot

    scotfoot Well-Known Member

    I just looked over the study again and find I have done the researchers a bit of a disservice in as much as I missed out the fact that they had a control group. The intervention group used minimal footwear only for everyday use and not for running type activities. At the end of the 6 month study the difference in toe flexor strengths between the intervention group and the control was large and is very unlikely to be explained by an increase in everyday activities.

    [​IMG]
     
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