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Mechanical control vs CNS stimulation

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Jun 8, 2010.

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    Hi Folks Ive been thinking again............

    Over the last few months we have been discussing leg stiffness and CNS control of knee, hip and ankle flexion and extension moments to control the leg stiffness. This change may or may not have an effect on other joint movement ie STJ pronation and supination moments which was the basis of the Does the tibia drive the foot or does the foot drive the tibia thread

    I´ve been doing some reading about Proprioception in another thread.

    Here websters online Dictionary take on Propriception

    If we put aside the foot type and "Proprioception" insole arguement as it´s been done to death.

    What go me thinking from the Websters info is that Proprioception can be learned. I also read the paper listed below which discusses nerve arrangement on the feet compaired to the hand. Which has got me thinking it there something to this....

    In the Leg stiffness thread we discussed CNS stimulation from different surface stiffness and it´s effects on leg stiffness through muscle contraction and thereafter joint motion.

    So ok if we use a device say a medial Skive we will look to by using an Orthotic reaction force (ORF) cause an extenal STJ supination moment, which may or may not cause STJ supination.

    Will we then be changing the bodies position in space, which would lead to a "Proprioception effect", which can be learned ? Therefore muscle work to hold the body in it´s new position, these muscle contraction lead to joint motion, different from before treatment, which leads to changes in joint motions ?

    Hope that makes sense, I´m bouncing some ideas around. Thinking out loud .
  2. Craig Payne

    Craig Payne Moderator

    Re: MMechanical control v´s CNS stimulation

    But, thats not proprioception - that could happen by an exteroceptive pathway.

    That was my big issue in previous threads on the propriceptive effects of orthotics .... what can an orthotic do in that regard ? ..... it can change loading on the plantar mechanoreceptors and that is some additional information the CNS can use to activate muscles etc ... but that is NOT proprioception, as this is happening by an exteroceptive pathway.

    That does not mean it actually happens and orthotics can and do work that way.

    We tested 3 inverted foot orthotics in 3 different sensory conditions (rough surface, normal surface, iced foot) and got exactly the same kinematic response for frontal plane calc movement .. ie the effect on rearfoot motion was all mechanical (we will publish it one day)
  3. Admin2

    Admin2 Administrator Staff Member

  4. Re: MMechanical control v´s CNS stimulation

    I guess thats why I put it "Proprioception effect", but exteroceptor pathway sounds good to me, look forward to reading the paper.

    Do you believe with enough "constant" change in information, a change caused by a stimulation of the exteroceptor pathway can cause a learned motion pathway. ie if stimulation occurs for long enough there are gait changes if we discuss orthosis.
  5. I don't think this neurological response to foot orthoses necessarily needs to be "learned" once the individual has learned to walk efficiently (probably by the age of 5). This is due to the fact that the individual's central nervous system (CNS) has already developed the capacity to alter the efferent output to their lower extremity muscles in a coordinated and efficient manner in order to keep the individual's center of mass balanced between their feet during standing and walking and allow the individual to remain upright.

    Therefore, when a foot orthosis is designed with a medial heel skive, for example, that creates an external subtalar joint (STJ) supination moment, that individual's CNS must "decide" whether to allow the STJ to supinate, how much it will allow it to supinate, or. instead will stabilize the STJ against supination motion or even make the STJ pronate in response to the medial heel skive. There is a common misconception among podiatrists that simply adding a varus or valgus wedge to an orthosis will cause the foot to invert or evert in the direction of the wedging, forgetting that the CNS has a huge controlling effect on this STJ motion/lack of motion, regardless of the shape of the wedge. These concepts need to be understood by all podiatrists.

    In order to clarify my thoughts further for, here is an excerpt from a Precision Intricast Newsletter I wrote on this same subject in October 2009:

  6. Thanks Kevin,

    In the example above when considering the Peroneals working to overcome the ORF of your device. If removed the CNS would adjust very quickly, the same as we have discussed in leg stiffness. When running over changed surface stiffness after the 1st contact with the surface and by the 2nd contact ( same side ) the CNS will have made adjustments to the leg stiffness required all things being equal according to research.

    From individual to individual there will be differences, but is there anyway appart from pain stimulation that we could use the CNS stimulation to our advantage ?

    Again, Appart from changing the foot-surface interface stiffness, (which we still don´t know how, when and why´s yet) for an individual ie what the person idea leg stiffness for the activity they are undertaking.

    I maybe going around and around in circles here and coming back to what drives what, but when considering Nigg preferred motion pathways, leg stiffness it´s really got me thinking.

    please note I´m not thinking about pushing on a place on the foot and calling it Proprioception, I´m more thinking about enhanced mechancial effects our device will have. I guess this more has to do with proximal changes from an orthotic rather than direct foot joint mechanical changes ie Peroneal contraction rather than direct STJ supination from Kevin´s post. or to put it another way muscle control of Joint ie internal moments rather than external moments from a device.
  7. The 'propriocepsis' discussion is in my opinion just a part of the discussion of neuromodular treatment through the plantar foot. Fact is that contraction of the intrinsic footmuscles is active when a foot is loaded. These muscles, all in the length of the foot, give a 'force closure' (the opposite of form closure)of the foot bones, supported by the plantar ligaments, which we find only with human.
    In my opinion is the contraction of these intrinsic muscles influenced by plantar facilitation of the footsole (baroreceptors), spine and alfa motor fibres. The gamma system (propriocepsis) is then a preset system, which constantly and rapidly adepts. In fact we have to talk about an alfa/gamma co-activation. So when we talk about these kind of insoles, we talk about exteroceptive insoles
    To read more about it and find some literature, please visit my website http://www.drbody.nl
  8. Brian A. Rothbart

    Brian A. Rothbart Active Member

    For the past 40 years I have been engaged in research, looking at the foot mechanics and how it impacts posture. The past 10 years I have published on much of my findings.

    I use the term pattens of proprioceptive stimulation to define the interaction between how the foot moves and the pattern of mechanical receptor stimulation that is a result of that particular foot motion. You may wish to give it another name. Be that as it may, I decided to use the term patterns of stimulation (the pattern of mechanical receptors being stimulated as the result of a specific foot motion).

    I have found that how the foot moves has a direct impact on the posture of the body, foot to jaw (see my two fairly recent publications in the JAPMA). That is, what I refer to as linear foot motion, where hip drive directs the motion in the STJ, I have found that the resulting posture is anatomical or nearly anatomically correct (ear over the lateral malleolus). However, when the foot escapes hip drive and enters gravity drive, I find several patterns of postural distortions (the most common being the kyphotic posture).

    What becomes even more interesting is the chronic pain patterns that develop from these postural distortions.

    Up until 2002, the questions that remained in my mind were (1)what caused the foot to escape hip drive and enter gravity drive and (2) how did distorted patterns of stimulation (resulting from gravity drive) lead to postural distortions.

    Over the past 10 years, I have proposed the following explanations to these questions:

    (1) In 2002 I published a paper describing two previously unrecognized embryological foot structures, the Primus Metatarsus Supinatus and the PreClinical Clubfoot Deformity. I suggested a model on how these two abnormal foot structures takes foot mechanics out of hip drive and into gravity drive.

    (2) Recently, I published a paper in Podiatry Review on a Neurophysiological Model that provides an explanation on how foot twist (hyperpronation resulting from gravity drive) could lead to postural distortions foot to jaw.

    I believe my research offers a starting point in the understanding on how foot pathomechanics results in postural distortions that will lead the patient into chronic musculoskeletal pain (foot to jaw)


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