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.


Is it all just too bloody complicated?

I’ve just got back from the ESMAC-SIAMOC meeting in Rome. We’ve been entertained royally for three days in the aulas and cloisters of the Thomas Aquinus University. It has once more been a fantastic opportunity to network and exchange ideas and on one level I come back rejuvenated and inspired.

I say “on one level” because on another level I’ve also come back somewhat disappointed – disappointed because there was little in the scientific programme which left me feeling I understood things better than I did before I arrived. A large number of papers could be summed up by the conclusion, “we understand this area less after performing this research than we did before we started”.  I don’t think it is just ESMAC-SIAMC that suffers in this way. I see it at most of the conferences I attend and in a lot of papers that I read (and, if I’m being honest, in some of the papers that I write).

Just two areas illustrate this. One is in the advanced and complex modelling that is so often the focus of contemporary biomechanics. We learnt (or had confirmed) in Rome that the results are highly dependent on the details of how the individual anatomy is parameterised and of the calibration processes used to define joint centres.  The overall conclusion is that we are less confident in the output of our simulations and models after we’ve performed this research than we were before. Of course it is important to know what the limitations of our research. At some stage, however, we will have to acknowledge those limitations and accept the conclusion that the biological complexity of the human neuromusculoskeletal system is just too great for us to stand any chance of applying these techniques usefully (at least not beyond the constraints of healthy people exercising tightly controlled tasks).

The other field is that of measuring spasticity. Seven or eight years ago I was really excited about the prospect of instrumenting clinical tests to quantify spasticity more rigorously. The results I’ve seen reported are really quite disappointing in that it seems that spasticity is a rather complex and badly behaved phenomenon that simply refuses to be measured.  I have little faith any longer that spasticity is a purely velocity dependent response  (Lance, 1980) and the additional complexity that is introduced when displacement, acceleration or even jerk might have to be considered removes any hope that we will ever understand how these components interrelate within the current paradigm.

One of the “advantages” of research leaving us less clear of what is happening than we were before is that it opens up the conclusion that “further research is required to better understand these phenomena”. Research thus begets research and the university departments rub their hands in glee at the prospect of more research grants, papers and citations. For many of us it leads to increased job security. We have a vicious circle that delights and thrives in creating complexity and chaos.

This is particularly bizarre in orthopaedic and rehabilitation fields (and perhaps more widely across health sciences) in that the tools we have to treat our patients are generally extremely blunt. Selective dorsal rhizotomy, intrathecal baclofen and botulinum toxin are the only tools we have to manage spasticity. At a clinical level the only decision we need to make is which, if any, of these to use. If we want our research to be clinically useful we need to concentrate on the simple questions that need to be answered before we turn our focus to the more complicated ones that don’t.

The small number of presentations that did impress me posed a research question in such a way that the answer actually improved my understanding of a given issue. Almost all of these resulted in me having a clearer, simpler view of the world after the presentation. This doesn’t necessarily require simplistic techniques. The walk-DMC scale that Kat Steele and Mike Schwartz proposed in their prize winning paper (page 25 of Abstract Book) uses a sophisticated technique. It is a technique, however, that has been appropriately selected to answer a well posed research question (Can we quantify the effect of disordered motor control on walking in children with cerebral palsy?). Once the appropriate techniques has been selected the answer is simple (Yes, at least on the basis of the preliminary analysis they presented).

One of the most ancient tests of the scientific quality is Occam’s Razor, that science (and our thinking in general) should be as simple possible but no simpler. It would be interesting to perform an audit of the presentations at any contemporary conference against this criterion. I suspect the results would be quite sobering.


Lance, J. (1980). Pathophysiology of spasticity and clinical experience with baclofen. In R. Feldman, R. Young & W. Koella (Eds.), Spasticity: disordered motor control (pp. 485-495). Chicago: Year book medical publishers.