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Back to that "normal"

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Jun 13, 2016.

  1. Members do not see these Ads. Sign Up.
    All, I spent a pleasant afternoon with a colleague recently where we looked at in-shoe pressure measures. I heard terms like "early heel lift", "normal pressure distribution" etc. I bit my tongue for the sake of the meeting. So, let's go back to first principles- who says when the heel should lift off the ground in a given individual? Why shouldn't this timing be variable between individuals given that if the time of heel lift should be seen as a phenotype (P) and that P= Genotype + Environment + (Genotype x Environment)? Moreover, that any difference in such timing can just be seen as variation and not something that needs to be "controlled" nor "corrected"?... Can't believe that in this day and age, we should believe in some sort of artificial dichotomy which allows us to label an individuals pressure analyses as "normal" versus "abnormal" is it just me?

    The whole concept of the "normative database" I just don't get... can someone please explain to me why comparing an individual to the mean of lots of individuals is a valid approach.... I just don't get it.. given that P= G + E + (Gx E)...?

    Your thoughts... because I'm honestly thinking of taking up a job in a supermarket that doesn't require for me to even think about this kind of bull**** any more.

    So, starter for ten: who says when exactly the heel should lift during walking gait, and why should it lift at this time... let's hunt down the references and see what we are left with other than conjecture.... nothing.
  2. blinda

    blinda MVP

    For what it's worth; whilst I didn't attend the Summer School this year, a colleague who did contacted me yesterday (about another matter) and she was incredibly enthused by comments that you made with regard to questioning normalization. Asda can wait.
  3. Kind, but seriously considering my exit options.
  4. efuller

    efuller MVP

    It does bring us back to the question of what measures should we treat before pathology occurs. That question has at least a couple of parts. Does a particular measure of the foot correlate with foot pathology? Do we have an intervention that has been shown to be effective in preventing that pathology?

    We can look at the high blood pressure model. Strokes....

    So, taking the tissue stress approach to the time of heel off in gait. Those with an early heel off will be spending more time on their forefoot and with greater length of time with a greater bending moment on the midfoot. Agreed there is no research now, but it could easily become someones project with multiple parts. Is timing of heel off consistent over time? Is there a correlation with early heel off (1 or 2 standard deviations from the mean time of heel off?) with metatarsalgia?, with arch strain? Does a heel lift actually change the force time integral for the forefoot. It's plausible.

    Tissue stress and STJ axis position. We need work here too. Can raters consistently sort axis position into groups of medial, avg. and lateral? Does a medial heel skive prevent pathology in feet with medially deviated STJ axes? etc.

    Both of those are plausible, but we haven't done the studies. So, I think we can have some measures, eventually, that we can compare to. However, those measures should have a plausible biologic explanation of why they are useful. Sub talar joint neutral and vertical heels don't really have an explanation of why there should be any correlation with pathology.

  5. I hear what you are saying Eric, but let me throw this in the mix, take two similar individuals subject 1 has twice the body mass as subject 2, but subject two spends twice the time on their forefoot as subject 1- as you know the impulse (force x time) will be the same in both subjects...

    Then we may have someone spending more time on their forefoot, but with stiffer metatarsals...
  6. Petcu Daniel

    Petcu Daniel Active Member

    I think the first question is what could means "lots of individuals" ? When I'm thinking at this question I make the link with determining the "functional groups" like in "Functional grouping of runners based on plantar pressure patterns" https://www.researchgate.net/public...of_runners_based_on_plantar_pressure_patterns

  7. timharmey

    timharmey Active Member

    when you are in the supermarket a blind woman asks you to pick her out an apple you say what size big? small? she says normal
  8. To me the first thing to do would be to partition the variance in "time of heel lift"... So list all of the factors which might interact to determine when the heel lifts....

    Thinking about it, you might need to first define why the heel lifts at all during gait?
  9. Maybe a side issue but why does it really matter if you have patients and they are happy?

    FWIW I have been having the similar issues my head hurts too much these days :bang: patients getting so much bs information
  10. Rob Kidd

    Rob Kidd Well-Known Member

    I swore to myself that I would not get involved in this stuff again - too many slaggings from the nonsense department; The key words here are normal-atypical-abnormal. Where do the boundaries lie - well that is up to science, underpinned of course by clinical evaluations (which in itself is science). I guess one should be reminded of standard deviations each side of the norm, but then, those in the know, already have this information. If it was down to me, I would start at Cochran and work out.
  11. STJ axis position is an interesting example since if memory serves the 42 degree:16 degree angle inclination that we were made to memorise in podiatry school stemmed from the work of Inman; that actually this angulation was the mean from the data set, but not a single individual within that data set had an axis angulated at 42:16.

    So, lets say we have a clinical method of measuring STJ axial position and a normative data set for STJ axial position the mean of which is 42:16, but no-one in that data set actually has that STJ axis position. We examine an individual and find that their STJ axial position is deviated markedly from this mean, should we be attempting to make this STJ axial position more like the mean?
  12. Simon:

    Hope your lectures at Biomechanics Summer School went well for you and all those involved. Looking forward to being there again next year.

    In my opinion, the term "normal" has been "ruined" for generations of podiatrists by Merton Root and colleagues by using the term "normal" to mean "ideal". This seems to be unique to podiatry but not to other health professions which seem to have no problems using the term normal to mean a range of values seen within the human population to describe structure, function, lab values, x-ray values, etc.

    I wrote a Precision Intricast newsletter on this very subject in September 2015, here it is, reprinted with permission:

  13. efuller

    efuller MVP

    I hadn't thought much about that before. You certainly can't correct for body mass. Thinking out load. Could you correct for foot size. Wider feet will have greater cross sectional area of ligaments. Does absolute resistance to bending correlate with foot size?

  14. efuller

    efuller MVP

    We need to look at the similarity and differences to other measures that we use to proactively treat. If you had a blood pressure of 200/120, BP would be similar to an extremely medially deviated axis in that there is a high probability that something bad will happen. However, the difference is that making the blood pressure closer to normal range is the goal, but you can treat a medially deviated STJ axis without making it normal. That said a calcaneal slide osteotomy can make the position of the STJ axis closer to normal. The question is whether the foot can be pain free by just changing the moment from ground reaction force. So, you could prevent problems without making the axis normal.

  15. Well you could correct for body mass, foot size etc. by creating cross-product variables etc. and normalising the data for these. So you'd need to look for co-variance between the predictors. Hence, that's why I was asking about the predictors of heel lift and partitioning the variance. So, what are all of the factors that you can think of that may influence the timing of heel lift?

    Ankle joint dorsiflexion stiffness, midfoot dorsiflexion stiffness, digital dorsiflexion stiffness... Foot length? Age? Gender? Walking velocity? etc. etc.
  16. efuller

    efuller MVP

    I'm not sure we care why the heel lifts early. We just need a way of assessing that it does lift earlier. My early attempt at force time integral on the forefoot doesn't work because someone with the same foot size could have 1.5 x the weight. Of course body mass will have an affect on tissue stress, but that might be independent of heel lift.

    We were taught in school that you assessed early heel off by where the swing leg was when heel off of the stance leg occurred. I still like this as it gives some indication of where the center of mass of the body is, in relation to the stance foot, when the heel lifts.

    One of my goals in thinking about this is to have some objective data on when to add a heel lift to the orthotic or the the shoe. An aside We would still have to see if a heel being helpful is even related to the timing of heel off in gait.

    Again thinking out loud,
  17. the reason we should care is that if we are applying a normative database then we need to subdivide that database to match the characteristics of the patient in front of us- so lets say we find a gender difference in timing of heel lift, if our patient is female- we need to compare to a "female normative database"; if there is a correlation between timing of heel lift and age, we need to compare to an "age matched normative database" etc. Do we compare blood pressure in 80 year olds to blood pressure in 16 year olds and employ the same normals?

    Which brings us back to how do we "know" when the heel should lift? I guess this is the real point. I think that the timing of heel lift will be variable across and even within individuals and that many factors will influence this. If we don't know what those factors are, we cannot normalise the data for these nor subdivide any normative database. Yes we are comparing apples with apples, but we know that there are different varieties of apples with different characteristics.

    For this reason, I like Tim Harmey's throw away comment regarding the "normal" sized apple. Even if we take "normal" to mean the arithmetic mean, the mean size of apple will vary across the differing varieties of apple- they're all apples, but in order to know whether the apple we have before us is "normal" in size, we need more details- specifically in this example the variety of apple. If we compared our Cox apple to a database that includes large cooking apples such as the Bramley, it may appear smaller than average (normal) when in reality it is above average size for a Cox. Do we see racial variation in the timing of heel lift?

    What if we compared an apple which has one month growth with apples that have been growing for 3 months...?

    Position of centre of mass (CoM) seems reasonable. But lets say we are comparing a normative database made up of fit athletic middle-aged males with an age matched male who is obese with a "beer-baby" for an abdomen? Pregnant female, with an age matched normative database of female who were not pregnant?
  18. Petcu Daniel

    Petcu Daniel Active Member

    Could you detail about swing leg and center of mass (related with stance foot) position?
  19. timharmey

    timharmey Active Member

    What I was tring to get to that we are always looking for the "normal" as a point of referrence.I train boxers some kid showns up does a bit of moving around the other trainer asks what do you think of him, I think through my memeory bank and think is he good /bad/ execeptional .We are always looking for a point of reference when we describe anything. Glad I was making some useful contribution rather than just being a pain in the arse , or my normal self
  20. But I'm guessing you wouldn't expect a fly-weight to move the same around the ring as a heavy-weight- right?
  21. Further thoughts. Lets say we put a pressure sensor in the gloves of your boxers, Tim. We measure the pressure for right hooks. We could measure the pressure for right hooks across all weight divisions and we'd probably get a normal distribution and a mean- let that be normal. Now, again I'm guessing and bowing to your superior knowledge, but lets compare a super heavy weight's glove pressure with a right hook to that mean- guessing its gonna be greater than the mean so is "abnormal" to the mean. Now collect a data-set for right hooks for super-heavy weights only- and compare that hit to the super-heavy weight mean; that same hit is gonna be much closer to the mean- right?

    So, there are reasons we need to subdivide the data in plantar pressure measures, just as there is a reason we subdivide by weight in boxing...
  22. efuller

    efuller MVP

    Single leg stance is the time from toe off of the contralateral foot to the time of heel contact of the contralateral foot. This is "normal" forward walking. At the instant of toe off of the contralateral foot, the stance leg is usually in front of the center of mass. The forward momentum of the body causes the body to rotate forward over the stance limb and the swing leg is moving forward faster than the body. There is a point when the swing leg passes the stance foot and this "normally" occurs when the center of mass is directly over the stance foot. The body continues to move forward and eventually the center of mass and the swing leg are in front of the stance leg.

    If the heel lifts off of the ground when the center of mass is directly above the foot, either the center of mass will be lifted, putting more strain on the arch, or there will have to be flexion of the hip and knee that will prevent raising of the center of mass. The increased flexion of the knee and hip could put more strain on both of those structures.

    When the heel lifts when the center of mass is in front of the stance leg, the body will not necessarily have to be raised vertically. Also, the heel can lift without ankle plantar flexion as the body pivots, in the sagittal plane, over the metatarsal heads. So, there can be less arch strain than if the center of mass is lifted.

  23. I like the CoM thing, I really do. So lets say I'm feeling sad and my shoulders are slouched, head is forward, I'm starring at the ground and resting my chin upon my upper torso as I walk- early heel lift? Next day I get good news and my shoulders are back, head held proud... normal heel lift?
  24. timharmey

    timharmey Active Member

    Have you ever seen the film Money ball some geek works out the best baseball players to buy based on stats and works magic( a true story)
    I know nothing about basball but the stats were performance based , ( most bases stolen!?!), maybe we need away of linking things like heel lift to functional outcome measures
  25. Petcu Daniel

    Petcu Daniel Active Member

    I found a nice representation of center of gravity relative to gait phases in Winter's article : "Human balance and posture control during standing and walking": https://www.semanticscholar.org/pap.../7760b2869f83ff04e595a39a0070283d2ea31c29/pdf


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