history

Mind your language

I’ve recently heard of a new history of gait analysis being written and been given a preview of the section on language development which I’ve been given permission to share.

The first task was obviously to understand how people walked. This proved more difficult than anyone imagined and at the end of the process everyone was considerably more confused than they were at the start. To cover this up they invented a new range of words and phrases.

Someone identified six determinants of gait which everyone agreed was a good thing despite very few of them really determining gait and the one that actually did being completely over-looked. The fourth and fifth were so vague as to be virtually useless but this was cunningly disguised by describing them both in the same paragraph which then looked nearly as long as the paragraphs describing the others.

The gait cycle was divided up in such a bizarre and counter-intuitive way that everyone thought it was a joke until they found it had been published in a text book and had to start using it. Mid-stance wasn’t in the middle of stance and terminal stance wasn’t at the end. There was a pre-swing but no pre-stance (which is actually more important). Single support was divided into two phases while swing was divided into three despite being the same period of time (but for the other leg). This made it virtually impossible to talk about what one leg was doing while the other leg was doing something else. At least this made things simpler. Shock-absorption started to be used for the phase when the upward movement of the body was being speeded up and push-off of for that when its downward movement was being slowed. Heel strike was adopted for the instant (or was it a phase?) when the foot contacted the ground despite many people not using their heel and very few of them striking the ground to any appreciable extent.

The plantar flexion knee extension couple was introduced despite the fact it clearly wasn’t a couple and three rockers invented despite no-one really knowing what a rocker was. The Americans assumed it was a quaint Anglo-Saxon term whilst the English assumed it was some new-fangled American word. Speakers of English as a second language just assumed they had slept through that lesson. When it was finally established that rocker didn’t have a specific meaning a fourth was added in celebration.

There was a backlash against terms that oversimplified complex concepts and very soon a demand emerged to balance this with other terms that would overcomplicate simple ones. A double bump in the ankle plantarflexion moment thus became a widely accepted alternative to “toe walking”. One group even went as far as to suggest that treatments that resulted in toe walkers achieving a heel contact be described as having effected a biomechanical transformation.

A challenge to the hegemony emerged from a perky Canadian who asserted that it was possible to understand walking by plotting joint moments. This was immediately recognised as a threat by the establishment. If walking could be understood then there might be an obligation on them to understand it. This might compel them to learn biomechanics which was clearly a bad thing. The solution was elegantly simple. They introduced some doubt as to whether internal or external moments should be plotted. (A radical splinter group even extending this to plotting some of the graphs upside down). This essentially made it impossible to categorically distinguish between the action of an agonist and its antagonist in normal conversation and successfully curtailed any useful contribution from the new approach. The status quo was re-established and the establishment was heard to exhale a collective sigh of relief.

Everyone understood what normal walking was but then some kind person realised that this forced them to talk about their patients as being abnormal which didn’t sound very nice. There was a competition to find an alternative which several people entered but nobody won. People still seemed happy to refer to these people as subjects. This sounded even less nice to some people but after the experience with normal they were largely ignored. A small group pointed out that referring to diplegic patients “put the disability before the patient” and went around scribbling out the term whenever they saw it and replacing it with patients with diplegia. At least this kept these people occupied and prevented them doing anything more damaging. In some fields the equivalent phrases were so unwieldy that they were replaced with abbreviations such as PwPD or PwMS. The end result of this process was thus to reduce groups of people who had previously had the dignity of being described by words to the ignominy of only ever being referred to by abbreviations.

The crowning glory was in achieving universal agreement that crouch gait was the biggest enemy but universal disagreement on what the term meant. Eventually it was decided to let everyone write their own definition – problem solved.

I gather this work is still in progress and if any readers would like to contribute additional examples of linguistic development in gait analysis as comments to this post then these will all be considered for inclusion in the definitive version.

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Demonstrating the gravity of the situation

I’ve been modifying e-Verne recently to make him a little more friendly to use on tablets and phones, particularly those running under iOS or Android (follow this link for tips). This has been in preparation for a Tutorial session I’m presenting at the GCMAS meeting next week in Portland. While I was doing the maintenance something reminded me of a picture in Braune and Fischer’s, “The Human Gait” (which was originally released in chapter form between 1895 and 1904) of a device to calculate the position of the centre of gravity of the whole body once you know the positions of the centre of gravity of the individual body segments. I scanned through through the book and this is the image that I remembered from page 127. The ingenious scaffolding mechanism moves the black spot in the centre to illustrate where the centre of gravity is.

Gravity man

I thought it might be interesting to add this functionality into Verne and below you can see how it looks. Use the “Mass centres” button to toggle the centre of mass positions on and off. The individual segment masses are depicted in black. The red and blue symbols are the centre of masses for the different limbs (femur, tibia and foot segments combined) and the green one that of the overall body. The area of the symbols are proportional to the mass of the different segments with the masses and centre of mass positions for the individual segments based on the data in David Winter’s book. Drag on the different segments to move them around (there are more instructions on the Verne page of this blog-site.

Whilst checking to see if I could save myself the walk to the scanner by surfing to  find if the image from The Human Gait was already on-line I was fascinated to come across a similar picture.

It’s from the catalogue of the German scientific instrument maker Eduard Zimmermann published in 1904. It’s labelled as a “Schwerpunktmechanismus nach Fischer”. They obviously sold well because they are still listed in the 1928 catalogue where a fuller description is available. It doesn’t say how big this was but it weighed 4.6 kg so much have been a fair size.

 

 

 

 

 

Well-heeled?

We’ve recently been doing some work to try and understand the transition between late swing and early stance to try and provide a better evidence base for my Why we walk the way we do video series. We’d been meaning to focus on late swing to start off with but some apparent artefacts in the data compelled us to look at what was happening in early stance.

After quite a lot of head scratching we found out that the artefact (in how markers on the medial, posterior, and lateral calcaneus move) can be explained quite easily if the calcaneus rolls forward in the first 50ms or so of stance (and takes the rest of the foot with it). This makes quite a lot of sense as the foot is rotating quite fast (approx. 200°/s) immediately before foot contact and we know that the foot is lowered to the floor over approximately this period. When I went and looked at a few x-rays this seems to relate very well to the functional anatomy of the calcaneus which has an almost circular posterior-distal aspect in the sagittal plane (red quarter circle in animation below). A recent paper on the anatomy of the heel pad confirms that it too wraps around onto the posterior aspect of the calcaneus which would allow cushioning of the calcaneus throughout any such rolling motion (blue quarter circle in animation below). I’ve not seen this mechanism described in exactly this way before but it is, of course, very similar to the Perry’s first rocker of stance.

Illustrative animation of rolling hindfoot (not-based on measurements)

Illustrative animation of rolling hind-foot (inspired by rather than based on our  measurements!)

 

We’re just about to submit the paper and I don’t want to write too much about it before it is fully peer reviewed but the results have made me to wonder why on earth we wear heels. Placing a heel of rectangular cross section under the calcaneus would pretty much destroy the potential for this rolling mechanism that the calcaneus appears to have evolved for. So why do we wear them?

It turns out that heels as an integral component of shoes are a relatively recent invention. As far as I can gather for most of history (and in most places on the globe) shoes had flat (no) heels (see pictures below).

Authentic reconstructions of 15th typical 15th century shoes

Authentic reconstructions of typical 15th century shoes

Heels first started to appear on riding boots in Europe in the 16th Century. Their role was not to help with walking but to retain the boot in the stirrup (and possibly to provide an anchor for spurs). Later on in the century  heels to started be incorporated in shoes worn at court particularly by rulers of short stature such as Queen Elizabeth I in England and Louis XIV in France (see picture below).

High red heels of Louis XIV from portrait by Hyacinthe Rigaud

High red heels of Louis XIV from portrait by Hyacinthe Rigaud

Once the monarch had adopted the practice of course it spread rapidly amongst the courtiers. For a large part of the 17th century relatively high heels were popular amongst both male and female members of the aristocracy.  There were even rules in France restricting the wearing of coloured heels to particular ranks within the aristocracy. During this period heels were essentially an indication of wealth and status and in English the term “well-heeled” is now used to refer to someone who is wealthy rather than someone who wears a particular style of footwear. During the French revolution there was a reaction against wearing heels as they were associated with the decadence of the pre-revolution court. Through much of the first half of the 19th Century heels were a comparative rarity. High heels never did take off for again men but returned in the mid-19th century for women particularly in Paris and New York

It is much less clear when the modern low heel came to be adopted as an integral part of the shoe for the ordinary (poor) people nor what its purpose is. Looking at the pictures on various web-sites suggests that the practice probably became common in the mid 18th century.   There is some suggestion that most of the wear on a shoe occurs under the calcaneus and that incorporation of a heel reinforces the sole in this area and can also be easily replaced if that wear becomes excessive. It wasn’t however until the mid 19th century that shoemaking started to become mechanised and modern footwear started to become affordable. Since this time the classic western male shoe has evolved very little. Almost all shoes these days have a heel even though materials are available which wear very little and shoe repair is becoming a rarer and rarer procedure.

Which all tends to make me think that in the modern world there isn’t any particular reason for heeled shoes and I wonder if we’d be better off without them. (Of course I could talk start talking about minimal shoes for running or negative here but that is a completely different subject).

Note: I’ve been quite dependent on a number of different web-sites for this information. It’s very difficult to determine quite how reliable those sites are but there does seem to be a general consensus on the salient points. 

DoG II – the evidence

This is a second post “celebrating” the 60th anniversary of the publication of the determinants of gait. I’d intended to start off with something positive in the first post, that the paper has been subjected to some misinterpretation, but Rodger Kram’s comment has made me reconsider that. Perhaps the notion that energy can be conserved by reducing the vertical excursion of the centre of mass is (CoM)  implicit in parts of the paper if never mentioned explicitly. This has even led me to speculate on how that might have arisen.

Anyway I’d tried to start with a positive because at some time we have to deal with the negatives. These are quite significant because there can be no real doubt that the determinants are wrong!

If we accept that a belief that minimising the vertical component of the centre of mass trajectory will reduce energy cost is implicit in the paper then the determinants are clearly wrong right from the start. There are multiple examples throughout dynamics of systems in which potential and kinetic energy are exchanged without requiring any external energy (the simple pendulum is the most obvious example). There is absolutely no reason why minimising CoM movement should necessarily reduce energy consumption. Even if CoM excursion did lead to increased energy expenditure we now know that most of the determinants don’t actually reduce it. Gard and Childress (1997) started off by showing that pelvic list occurs at the wrong time and a little time later (1999) that the same is true of stance phase knee flexion. A short time later Kerrigan et al. showed that pelvic rotation has little effect on CoM height either.

The stance phase determinants (pelvic list, stance phase knee flexion) become even more bewildering if the aim is to smooth the trajectory of the CoM, because the trajectory is smooth already. Compass gait results in the CoM moving along a circular arc and there can be few trajectories that are smoother than that!

The final nail in the coffin was delivered by both the Chicago (Gard and Childress, 2001) and Boston (Kerrigan et al. 2000) groups establishing that Saunders, Inman and Eberhart had missed the most important determinant of CoM movement  which is movement of the foot and ankle and particularly heel rise in late stance.

We thus have a triple whammy:

  • the axioms on which the determinants are inappropriate (either because the trajectory of the CoM in compass gait is already smooth or because there is no particular reason why reducing its vertical excursion should reduce energy cost)
  • three of the major determinants don’t alter gait in the way the authors claimed
  • the authors missed the most important determinant that does!

I’m not the first to outline this of course. Art Kuo made a similar summary in an article in 2007. The most bizarre commentary, however, is that of Childress and Gard published in the third edition of Human Walking (2006). There’s nothing bizarre about the commentary but there is about its location- immediately after a full reproduction of the chapter as published in previous editions. We thus have a “keynote” chapter in a major text-book followed by a two page summary of why the chapter is wrong. How weird is that?

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Childress, D. S., & Gard, S. A. (2006). Commentary on the six determinants of gait. In J. Rose & J. G. Gamble (Eds.), Human Walking (pp. 19-21). Philadelphia: Lippincott Williams and Wilkins.

Gard, S., & Childress, D. (1997). The effect of pelvic list on the vertical displacement of the trunk during normal walking. Gait and Posture, 5, 233-238.

Gard, S., & Childress, D. (1999). The influence of stance-phase knee flexion on the vertical displacement of the trunk during normal walking. Archives of Physical Medicine and Rehabilitation, 80, 26-32.

Gard, S., & Childress, D. (2001). What determines the vertical displacement of the body during normal walking? Journal of Prosthetics and Orthotics, 13, 64-67.

Kerrigan, D. C., Della Croce, U., Marciello, M., & Riley, P. O. (2000). A refined view of the determinants of gait: significance of heel rise. Archives of Physical Medicine and Rehabilitation, 81(8), 1077-1080.

Kerrigan, D., Riley, P., Lelas, J., & Della Croce, U. (2001). Quantification of pelvic rotation as a determinant of gait. Archives of Physical Medicine and Rehabilitation, 82, 217-220.

Kuo, A. D. (2007). The six determinants of gait and the inverted pendulum analogy: A dynamic walking perspective. Hum Mov Sci, 26(4), 617-656.

60 years of the determinants of gait: a misconception

The month of July 2013 marks the 60th anniversary of the publication of The Major Determinants of Normal and Pathological Gait by J B dec M Saunders, Verne Inman and Howard Eberhart.  This is a seminal paper in the history of gait analysis which was revered for many years and is the foundation of the description of normal walking in many text books.  More recently, however, it has come in for substantial criticism.

three determinants

The first named author, John Bertrand deCusance Morant Saunders, was a medically trained Professor of Anatomy at the University of California who was born in South Africa of Scottish descent. The story is that he needed his name on a paper to justify a trip to the Joint Meeting of the Orthopaedic Associations in London in 1952 and Inman and Eberhart obliged. There is little doubt that the ideas were those of Inman, a pioneering Orthopaedic Surgeon, and Eberhart,  an engineer. (Inman first met Eberhart when amputating his leg after a wartime accident at the time when he had been asked to establish the National Research Council Advisory Committee on Artificial Limbs. He invited Eberhart, originally a civil engineer, to join him and the partnership continued for the next thirty years).

Over the month I intend to write a series of posts celebrating this anniversary by looking at different aspects of the paper.  In this post I’d like to dispel one of the myths about the paper which is that it states that the aim of walking is to minimise the excursion of the centre of mass. In a significant review article, for example, Art Kuo (2007) writes “The six determinants of gait theory proposes that a set of kinematic features help to reduce the displacement of the centre of mass. It is based on the premise that the horizontal and vertical displacements are energetically costly”. 

An earlier paper by Ortega and Farley (2005) starts with an almost identical quote which drove the authors to train participants to walk with a nearly flat trajectory of the centre of mass. They then showed that it took nearly twice as much energy (oxygen) to walk a given distance with the flattened trajectory than with the normal trajectory. Gordon, Ferris and Kuo (2009 – who I think did the work earlier but published it considerably later than Ortega and Farley) conducted a very similar study and came up with essentially the same results. The introduction of that paper is interesting in describing how “at least a dozen text books have interpreted [Inman’s] work as meaning it is desirable to minimise or reduce COM movement during walking” and giving an overview of how the ideas have developed through these.

What is interesting though is that nowhere in the original paper (nor in the extended versions that have appeared in the three editions of the book Human Walking) can I find any statement by the  authors that minimisation of the COM movement is the aim of walking. What thy actually said was this:

Translation of a body in straight line with the least expenditure of energy may be achieved mechanically by the use of a wheel, but it is quite impossible by means of bipedal gait. The next most economical method would be the translation of the body through a sinusoidal pathway of low amplitude in which the deflections are gradual. Since force is equal to mass times acceleration and acceleration is a function of time, abrupt changes in the direction of the centre of motion compel a high expenditure of energy. In translating the centre of gravity through a smooth undulating pathway of low amplitude the human body conserves energy; and, as we shall see in considering pathological gait, the body will make every attempt to continue to conserve energy.

What they are proposing is that the body acts to ensure a smooth trajectory not necessarily one of minimal vertical displacement. They start off by describing compass gait, moving with fixed knee with no foot and the problem that they identify with this is that “at the point of intersection with the arcs, the abrupt change in the direction of the forward acceleration [I think they actually mean vertical component of velocity – RB] would require the application of a force of considerable magnitude”. This is actually extremely close to the hypothesis of the Dynamic Walking Group that one of the principal energy costs of walking is the requirement to redirect the centre of mass velocity during step to step transitions (Kuo et al. 2005) despite a contention that  their approach is the antithesis of Inman and Eberhart’s (see Kuo  2007). The six determinants proposed in the original paper are then strategies to smooth the trajectory of the COM but not necessarily to reduce it.

So where did the original and perfectly sensible views of Inman and Eberhart get distorted? Gordon et al. (2009) quote Perry (1992) as saying “minimising the amount that the centre of gravity is displaced from the line of progression is the major mechanism for reducing the muscular effort of walking, and consequently, saving energy”. Perry, of course, trained under Inman, and it may be that like so many pupils it is she that has misrepresented the ideas of her teacher. As an engineer myself, however, I’d take the personal side out. I’d see the original and valid ideas as indicative of the potential for progress when clinicians and engineers come together to address the challenges of clinical biomechanics. The misrepresented and invalid ideas appear when clinicians think they can go it alone!

That’s it for this post. I’ve emphasised one particular aspect in which I think the work has been unfairly criticised. In later posts I’ll look at some aspects where criticism may have been more justified as well as examining the popular appeal of the approach

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Gordon, K. E., Ferris, D. P., & Kuo, A. D. (2009). Metabolic and mechanical energy costs of reducing vertical center of mass movement during gait. Arch Phys Med Rehabil, 90(1), 136-144.

Kuo, A. D., Donelan, J. M., & Ruina, A. (2005). Energetic consequences of walking like an inverted pendulum: step-to-step transitions. Exerc Sport Sci Rev, 33(2), 88-97.

Kuo, A. D. (2007). The six determinants of gait and the inverted pendulum analogy: A dynamic walking perspective. Hum Mov Sci, 26(4), 617-656.

Ortega, J. D., & Farley, C. T. (2005). Minimizing center of mass vertical movement increases metabolic cost in walking. J Appl Physiol, 99(6), 2099-2107.

Perry, J. (1992). Gait Analysis. Thorofare: SLACK.

Saunders, J. D. M., Inman, V. T., & Eberhart, H. D. (1953). The major determinants in normal and pathological gait. Journal of Bone and Joint Surgery, 35A(3), 543-728.