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Hydraulically discrete fascicles in skeletal muscle

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Jan 4, 2016.

  1. scotfoot

    scotfoot Well-Known Member


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    The following is purely speculative

    It has been shown experimentally that transverse compression of skeletal muscle can ,under some circumstances ,cause the force generated by the muscle during contraction to be reduced (1) .
    It seems reasonable to think that if the more superficial parts of a muscle such as the pectoralis major contract to apply a force then the deeper fibers of the muscle will be subject to transversal loading .
    For me this raises the question of whether the transversal loading of the deeper fibers by the more superficial reduces the contribution that the deeper fibers make to the overall force production of the muscle or if the anatomy of skeletal muscle muscle allows the deeper fibers to function fully without a reduction in force production .

    Skeletal muscle consists of fibers covered by a thin membrane called the endomysium . Fibers are further arranged into bundles or fascicles which are covered by a relatively thick membrane called the perimysium which is generally regarded as a structure which shapes and organizes the muscle fibers and also allows the transmission of lateral contractile movements .
    If the perimysium is sufficiently impermeable then might it be possible that each fascicle is able to function as a hydraulically discrete unit with little or no reduction in force production regardless of the transversal forces generated by more superficial parts of the muscle .

    The following analogy may help to explain the idea -

    -Imagine a fish tank 20 cm long, 4cm wide and 30 cm high.
    Next imagine you place 10 small eels of about 20cm in length in the tank and add some water so that it just covers the eels .Each eel represents a single muscle fiber and these are free to move around although for the sake of the analogy lets assume the eels maintain a length wise orientation along the tank .

    Now imagine adding a 10kg weight lowered on top of the eels . The weight would be a good fit for the tank with just enough room at the sides for water to flow easily between the tank and the weight .

    The weight will bear down on the eels ,squeezing away the water around them and pinning the eels flat . This represents the effects of transverse compression on the deeper fibers of a large skeletal muscle with curved fibers (2) during contraction of that muscle .

    So does the anatomy of skeletal muscle provide any means by which the deeper fibers of a muscle can function normally under transverse load ? Possibly .

    Firstly take our eel, water, tank system but this time place the eels and the water in a latex bag ,seal the bag and place it in the tank .

    Next lower the weight down on top of the bag full of eels and this time the eels are not crushed but instead are free to move around in the pressurized water . The latex bag represents the perimysium .
    The idea is that so long as a skeletal muscle fascicle is bounded on all sides by other fascicles a hydraulically discrete unit capable of elastic deformation can exist which would allow the muscle fibers within the fascicle to contribute fully to the contraction of the muscle .

    This idea may already have been described but I can't find anything along these lines in the literature .

    Any thoughts ?

    Gerry

    Gerrard Farrell

    Glasgow


    1 Comput Methods Biomech Biomed Engin. 2014;17(3):217-29. doi: 10.1080/10255842.2012.675056. Epub 2012 Apr 19.
    Work partitioning of transversally loaded muscle: experimentation and simulation.
    Siebert T1, Till O, Blickhan R.

    2
    J Appl Physiol Respir Environ Exerc Physiol. 1984 Feb;56(2):287-95.
    Intramuscular fluid pressure during isometric contraction of human skeletal muscle.
    Sejersted OM, Hargens AR, Kardel KR, Blom P, Jensen O, Hermansen L.
     
  2. scotfoot

    scotfoot Well-Known Member

    This is a more fully explained version of the above -----

    Hydraulically discrete fascicles in skeletal muscle
    The following is purely speculative and relates to skeletal muscle and medial arch supports .

    It has been shown experimentally that transverse compression of skeletal muscle can ,under some circumstances ,cause the lateral force generated by the muscle during contraction to be reduced (1) .
    It seems reasonable to think that if the more superficial parts of a muscle such as the pectoralis major contract to apply a force then the deeper fibres of the muscle will be subject to transversal loading .
    For me this raises the question of whether the transversal loading of the deeper fibres by the more superficial reduces the contribution that the deeper fibres make to the overall force production of the muscle or if the anatomy of skeletal muscle allows the deeper fibres to function fully without a reduction in lateral force production .

    Skeletal muscle consists of fibres covered by a thin membrane called the endomysium . Fibres are further arranged into bundles or fascicles which are covered by a relatively thick membrane called the perimysium which is generally regarded as a structure which shapes and organizes the muscle fibres and also allows the transmission of lateral contractile movements .
    If the perimysium is sufficiently impermeable then might it be possible that each fascicle is able to function as a hydraulically discrete unit with little or no reduction in force production regardless of the transversal forces generated by more superficial parts of the muscle .

    The following simple analogy may help to explain the idea -

    -Imagine a fish tank 20 cm long, 4cm wide and 30 cm high.
    Next imagine you place 10 small eels of about 20cm in length in the tank and add some water so that it just covers the eels .Each eel represents a single muscle fibre and these are free to move around although for the sake of the analogy lets assume the eels maintain a length wise orientation along the tank .

    Now imagine adding a 10kg weight lowered on top of the eels . The weight would be a good fit for the tank with just enough room at the sides for water to flow easily between the tank and the weight .

    The weight will bear down on the eels ,squeezing away the water around them and pinning the eels flat . This represents the effects of transverse compression on the deeper fibres of a large skeletal muscle with curved fibres (2) during contraction of that muscle .

    So does the anatomy of skeletal muscle provide any means by which the deeper fibres of a muscle can function normally under transverse load ? Possibly .

    Firstly take our eel, water, tank system but this time place the eels and the water in a latex bag ,seal the bag and place it in the tank .

    Next lower the weight down on top of the bag full of eels and this time the eels are not crushed but instead are free to move around in the pressurized water . The latex bag represents the perimysium .
    The idea is that so long as a skeletal muscle fascicle is bounded on all sides by other fascicles,under similar pressure a hydraulically discrete unit capable of elastic deformation can exist which would allow the muscle fibres within the fascicle to contribute fully to the contraction of the muscle .

    ( Obviously the above analogy is a gross simplification of a far more complex situation.)

    A recent study (3) has shown that work partitioning of transversally loaded muscle can reduce the transverse load generated by the muscle and greatly reduce the rate of force production . However I feel that the experimental rig used by Siebert and his co workers does not accurately represent the type of transverse loading applied by the contacting superficial fibres of a muscle to the deeper layers of the muscle .

    Going back to the eels/water /tank/bag analogy lets now assume that the weight used to represent the pressure from superficial fibre contraction now has a distinct non compressible ridge running transversely across its base at its midline .

    Now when the weight is lowered onto our bag of eels (fascicles and muscle fibres ) the ridged area will press into the bag in its mid section bypassing the protective hydraulic system and applying direct pressure from above onto the eels reducing their ability to move . I believe this is what may be happening in the experiments conducted by Siebert . The? hydraulically discrete fascicle system ? proposed can only function if the fascicles are completely surrounded by fascicles at similar pressures .


    Change in muscle shape during concentric contraction


    When a muscle such as the pectoralis contracts to apply force it shortens and the muscle belly cross section increases . So how can this increase in muscle belly volume happen with as little work partitioning as possible . Again I feel the answer may lie in part in the ?Hydraulically discrete fascicle system ?.

    Back to balloons !

    If a long modelling type party balloon is filled with water and sealed then the pressure of the water will be the same at all points inside the balloon . However ,examination of the balloon will reveal the ends are under far less pressure than than the midsection since the ends have a reduced radius . This is explained by Laplace?s law .

    The ends of balloon can be pushed in fairly easily resulting in a slight increase in the area of the midsection .
    Perhaps then when a fascicle contracts the greatest movement is at the ends of the fascicle allowing force to be transferred to the tendon whilst reducing work partitioning and allowing a degree of muscle gearing (Pascal ) in the midsection .


    So what does all this have to do with footwear .
    Well as Sweeney et al (4) confirm orthoses with a medial arch support cause the plantar musculature to be compressed and so I believe the functioning of medial arch supports and the volume and contractile state of the plantar intrinsics are highly inter related .





    Any thoughts ?

    Gerry

    Gerrard Farrell

    Glasgow


    1 Comput Methods Biomech Biomed Engin. 2014;17(3):217-29. doi: 10.1080/10255842.2012.675056. Epub 2012 Apr 19.
    Work partitioning of transversally loaded muscle: experimentation and simulation.
    Siebert T1, Till O, Blickhan R.

    2
    J Appl Physiol Respir Environ Exerc Physiol. 1984 Feb;56(2):287-95.
    Intramuscular fluid pressure during isometric contraction of human skeletal muscle.
    Sejersted OM, Hargens AR, Kardel KR, Blom P, Jensen O, Hermansen L.

    3 Work partitioning of transversally loaded muscle ...

    www.ncbi.nlm.nih.gov/pubmed/22515574


    by T Siebert - ‎2014 - ‎Cited by 17 - ‎Related articles
    19 Apr 2012 - Work partitioning of transversally loaded muscle: experimentation and simulation. Siebert T(1), Till O, Blickhan R. Author information:
    4
    Effect of antipronation foot orthosis geometry on ...

    www.ncbi.nlm.nih.gov/pubmed/26465089
    by D Sweeney - ‎2015 - ‎Related articles
    Effect of antipronation foot orthosis geometry on compression of heel and arch soft tissues. Sweeney D, Nester C, Preece S, Mickle K. This study aimed to .
    Last edited by Gerrard Farrell; 02-13-2016 at 11:56 AM. Reason: typo
     
  3. scotfoot

    scotfoot Well-Known Member

    Dear admin
    With regard to the above
    If a long modelling type party balloon is filled with water and sealed then the pressure of the water will be the same at all points inside the balloon . However ,examination of the balloon will reveal the ends are under far less PRESSURE than than the midsection since the ends have a reduced radius . This is explained by Laplace?s law .

    SHOULD READ

    If a long modelling type party balloon is filled with water and sealed then the pressure of the water will be the same at all points inside the balloon . However ,examination of the balloon will reveal the ends are under far less TENSION than than the midsection since the ends have a reduced radius . This is explained by Laplace’s law .

    I would be grateful if you could change this and then delete this post .

    Cheers Gerry
     
  4. scotfoot

    scotfoot Well-Known Member

    Hi Simon
    . I would be interested to hear what you think about the my theory of hydraulically discrete fascicles . I feel that without this system larger animals ,with greater muscle mass would not be viable . This includes us .

    What say you ?

    Regards

    Gerry
     
  5. I say: how does the recruitment of motor units and the modulation of their firing frequency influence this idea? But would add that I'm no expert on muscle physiology nor micro structure.
     
  6. scotfoot

    scotfoot Well-Known Member

    Good question . As far as I can see the theory does not contradict any of the know facts about how muscles function but merely suggests a way in which the structures , know to be present ,may interact to prevent wasteful work partitioning .
    If present,the system would simply mean that to produce a given force fewer motor units at lower frequency are required .

    I have had some feedback from senior research physiologists both of whom regard the theory in general as " entirely plausible " .

    I believe the discrete fascicle system may allow the intrinsics of the foot to function even when they are under substantial compressive load .

    Regards

    Gerry
     
  7. You are probably better off asking Luke Kelly his opinion on this, he is also a member here. I just had an e-mail from Declan Sweeney about something else and have informed him that you are discussing his work here, so he may comment if he has anything to add.
     
    Last edited: Nov 18, 2016
  8. Here's a question: if transverse compressive load reduces the force produced by the muscle and orthoses with a medial arch support cause the plantar musculature to be compressed more as you suggest, then we should see increased recruitment at a higher frequency with foot orthoses in-situ, but do we? If so, this might explain the increase in muscle strength reported in concert with the wearing of foot orthoses. But back to the original question: do we?

    Except that now, with the foot orthoses in-situ, the plantar intrinsics should be required to provide a smaller component of force to maintain the same kinematic pathway because the foot orthoses are providing an external source of "arch support" forces, so the intrinsics don't have to provide such high forces anyway. This is the argument often put forward by those who pretend that foot orthoses "weaken muscles", even though the evidence tells us that they do not.

    However, physics tells me that with increased external compressive load in the medial longitudinal arch of the foot, the force component generated by the plantar intrinsics can be reduced and the same kinematic pathway can be maintained anyway, so why the need to have this mechanism that you propose? Moreover, if you follow the "belief" that we were "designed" to ambulate on softer surfaces, then such surfaces should increase the compressive load into the medial longitudinal arch in much the same way that foot orthoses do; so once again: why the need?

    Let's go back several evolutionary steps to the "origin of muscle fascicles"- what would be the evolutionary driver for your theory? I'm guessing neither evolution nor "God" had foot orthoses in mind when designing these structures since foot orthoses didn't exist back then...

    Out of interest Gerry, what is that you do for a living and why the obvious interest in the plantar anatomy of late?
     
    Last edited: Nov 18, 2016
  9. scotfoot

    scotfoot Well-Known Member

    I have already said elsewhere on the arena that I believed the mechanism by which medial arch supports may increase foot muscle strength is via work partitioning of the involved muscles . But would an arch support work as well if there were no intrinsic muscles between the fascia and the bony arch of the foot ? What would press on what ?

    Do orthotics work ? Of course they do . Do they weaken feet ? No ,they strengthen feet and perhaps by the a mechanism involving work partitioning .

    Evolutionary driver for my theory ? The idea is not that the intrinsic muscles are compressed only in the case of an orthotic with a medial arch support . It is that the are compressed as the bony arch of the foot lengthens and the fascia tightens during early stance whether an orthotic is present or not . If you like they are a bit like the meat in a sandwich helping to spread load within the structures of the foot . They can fulfill this cushioning function and still apply undiminished force at the points of insertion provided a discrete fascicle system exists . You may well not agree but do you see what I am trying to say ?
    As to the other points you have raised -

    I am a dentist by profession .

    I believe that the foot is greatly under researched and find anatomy and physiology fascinating .

    I would love to chat to Dr Luke Kelly and believe his Phd work may eventually be seen as seminal .

    Regards

    Gerry
     
  10. But you didn't answer the question: do we see increased recruitment at a higher frequency with foot orthoses in-situ?


    Not sure what you mean by "work as well"? We know that foot orthoses are employed in an intrinsic minus foot-type with success. Without the muscles, the plantar skin of the foot and it's hosiery would still press against the superior surface of the orthosis and the orthosis would press back with an equal and opposite force just as it does with the muscles present.

    Load sharing in isolation does not explain an increase in muscle strength as I suggested above. The key here is that same old question: do we see increased recruitment at a higher frequency with foot orthoses in-situ?

    My understanding of Luke's work is that during the first half of stance the intrinsics are working eccentrically modulating the loading rate of the plantar-fascia, storing elastic strain energy which is returned during the propulsive phase; as such I think elongation is of greater significance than compression. If cushioning was the primary purpose, it should be better achieved with a fat pad system similar to that observed beneath the heel. Indeed, of interest is how the fat pad in the medial longitudinal arch of the infant diminishes with increasing age and the onset of bipedal walking. Besides, I really don't think you're going to get an awful lot of compression in the medial longitudinal arch in a rectus foot-type ambulating on stiffer surfaces.

    You got bored of looking into peoples mouths? I think Lukes work has made an important contribution, but I think even he would agree that the seminal work in this field was carried out by Basmajian, Mann and Inman.
     
    Last edited: Nov 19, 2016
  11. scotfoot

    scotfoot Well-Known Member

    Hi Simon
    Effect of antipronation foot orthosis geometry on ...

    www.ncbi.nlm.nih.gov/pubmed/26465089
    by D Sweeney - ‎2015 - ‎Related articles
    Effect of antipronation foot orthosis geometry on compression of heel and arch soft tissues. Sweeney D, Nester C, Preece S, Mickle K. This study aimed to .

    With regards to the above perhaps when you next speak to Declan you could ask him if they looked at the disposition of the tissues on the medial aspect of the foot with the foot in a loaded and unloaded condition but without an orthotic device present . Such information is likely to exist only in anecdotal form but I would still be interested to hear .


    "But you didn't answer the question: do we see increased recruitment at a higher frequency with foot orthoses in-situ?" in answer to this could I refer you to the paper and comment below .

    Shoes alter the spring-like function of the human foot during running

    rsif.royalsocietypublishing.org/content/13/119/20160174.full.pdf
    by LA Kelly - ‎2016
    15 Jun 2016 - Luke A. Kelly, Glen A. Lichtwark, Dominic J. Farris and Andrew Cresswell. Centre for ... intrinsic foot muscles using intramuscular electromyography. In contrast ...



    Comment -
    Gerry • 5 months ago
    Interesting results.
    However, might another interpretation of the results be that the compression of the intrinsic muscles in the midfoot/medial areas of the contoured supportive running shoe leads to work partitioning and hence harder working intrinsics ?

    note for clarity - the comment was placed by me on a Royal Society blog site and relates to the paper by LA Kelly -2016 Shoes alter the spring-like function of the human foot during running
     
    Last edited: Nov 19, 2016
  12. Interesting, you can speak to Declan yourself via a private message here: he is listed as Deco, similarly with Luke. While the shoe versus no shoe is interesting and may offer some insight, a shoe is not a foot orthosis...

    Anyway, look forward to reading your research on this if and when it is published. Good luck.
     
  13. scotfoot

    scotfoot Well-Known Member

    Question ; If a group of individuals studying the energetics of the foot were to read this thread and be influenced by its contents , could it be referenced in any subsequent academic paper ? Actually , in general ,can blog site material be referenced ?
     
  14. scotfoot

    scotfoot Well-Known Member

    Question
    For the sake of argument let's assume that posts 1 and 2 constitute a grounded theory about muscle function . In the theory ,water filled balloons , coupled with the possibly , functionally significant impermeability of the connective tissue around muscle fascicles , are used in a thought experiment to explain aspects of muscle function related to the incompressible nature of fluids .

    Now , speaking hypothetically , let's say some time after posts 1 and 2 were published a group of scientists produced a paper on the role of the incompressible nature of fluids in muscle function that used a water filled balloon or the like , as part of an experimental set up .
    If I wanted inquire further about their paper how would I go about this ?
     
    Last edited: Aug 25, 2018
  15. scotfoot

    scotfoot Well-Known Member

    Wow . Just put - "incompressible fluid"" muscle function " - into google search engine . Nothing really before Feb 2016 but all the rage now .
     
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