New goals for Podiatric Biomechanics

Clearly there is circadian variation. On a similar track, I heard Simon Bartold describing a link between running injuries in females and their menstrual cycles.

I guess this is one of the reasons we perform within-day and between-day error experiments on our measurement systems, so that these varaitions are taken into account when we evaluate our results. So I'm not sure we are ignoring it?

 

I wouldn't be so sure of that, Dave. Research done in subjects running in running shoes of varying midsole durometer produced some interesting results. The GRF peaks were actually decreased in some runners as they ran in a shoe with a more firm (i.e. higher durometer) midsole and GRF increased as they ran in a lower durometer midsole shoe. The subject was supposedly able to adapt their landing style to the shoe midsole durometer. I don't know of similar research in walking but I'm certain that some people may actually walk with less internal forces on hard surfaces than on soft surfaces due to alteration in gait style, preactivation of muscles, etc.

The point is that David Holland commonly uses the concept of walking on hard, flat surfaces to explain many mechanically-based pathologies in the foot and lower extremity, which is a factor that, like gravitational acceleration, we can't readily change as clinicians. While I agree that certain pathologies are caused by incessant walking on hard surfaces in our society, to make this a central focus of mechanically-based foot pathologies is, at best, nonsense.

Any intelligent clinician will advise their patients to modify their work activities or even change jobs if conventional measures of reducing the tissue stresses on the injured structural components of the foot and/or lower extremity have failed. However, the surfaces we walk on are not the cause of most foot and lower extremity pathology, as David likes to often suggest. In fact, I propose that the surfaces we walk on in today's society may help prevent ankle sprains, reduce the incidence of falls, prevent puncture wounds to the plantar foot and allow easier access to healthy activities such as bike riding, in-line skating and running than if we all lived in a totally natural environment as our early ancestors did.

David Holland's argument of the importance of hard,flat surfaces in injury production is certainly not new or unique and I think that it is nothing more than an old idea that should be acknowledged as one of the many possible factors that may cause mechanically-based foot and lower extremities in some individuals.

 

Simon

(Not patronising but just for the benifit of those who may not know (before you bite my head of Simon))Pdef = dEfoot/dt, dEfoot = distance, assuming that dt is displacement of time then this formula is basically acceleration or rate of change of velocity. Large deformation / large time displacement = large attenuation of force.
The faster the foot decelerates the more force F=MxA. Which proves that hard surfaces do = more force applied to the foot since deformation is small over a small time displacement. If you wished to define this in terms of work done over time ie power then we need to know the mass of the subject.
But the formula is work = mass x distance, power = work/time. Large mass moved a large distance in a short time = great power. Energy transfer may give a better picture but the maths gets quite involved. But basically is the kinetic energy = 1/2Mxv^2 KE+ Potential energy=MxGxH PE so (Pe1+Ke1)-(Pe2+Ke2)= energy transfer potential energy becomes stored elastic energy and Ke ends up in the earth and heat. For more info read Biomechanics and Human motor control of movement. David A Winter.
Anyway if you are saying that the heel pad deforms to attenuate force then this would be a indepent constant not related to the hardness of the surface walked on. Regarding your question then (without data) I would assume that in the unshod foot the Pdef would be higher in terms of force attenuated ie more force aplied to the foot. In terms of power this is, i think, an indeterminate calculation since as velocity approaches zero power becomes zero yet force becomes very high. This would be similar to when the achilles tendon is under high tesion but the muscle is in isometric contraction, there is a lot of tensile force and high joint moments but power is zero as no work is being done. Except that the muscle is using energy and doing physiological work.
I can see where your coming from Simon but then this may only strengthen the case for the hypothesis. Since shoe manufactures spend a lot of time and energy promoting 'shock absorbing' heels on sports shoes is this not acnowledging that the surfaces we want to run on are potentially hard and give rise to the possibility of injury over prolonged activity.

As far as I know not many people live on *frozen lakes and sun baked desert and maybe the one's that did (*in the ice age for instance) had a high prevelance of foot pathology. Unless of course they all wore Nike trainers but more likely they wore some sort of protection from the cold, which as well as being insulating was no doubt 'shock absorbing'.

Another point is that people who walk on hard surfaces without shoes may limit the total force applied to the foot by some method such as bending the knees more, like one does when walking on a pebble beach.

I realise that this is a marketing campaign but I think you will find that P Vasyli and company wrote some research along these lines but it could be biased.
Anyway the point is that its not off the wall or a unique theory

But its all very interesting to discuss.

Cheers dave smith

 

Kevin

quote
"I wouldn't be so sure of that, Dave. Research done in subjects running in running shoes of varying midsole durometer produced some interesting results. The GRF peaks were actually decreased in some runners as they ran in a shoe with a more firm (i.e. higher durometer) midsole and GRF increased as they ran in a lower durometer midsole shoe. The subject was supposedly able to adapt their landing style to the shoe midsole durometer. I don't know of similar research in walking but I'm certain that some people may actually walk with less internal forces on hard surfaces than on soft surfaces due to alteration in gait style, preactivation of muscles, etc."


Yes I pretty much agree with what you are saying,(my last post hinted at the possibility of changing gait style to suit the terrain) but these result can have a very complex explanation. The difference in peak forces between shod and unshod feet is often quite small. However force / time can vary a lot. often unshod feet show high peaks at heel strike first 25m/s that shod feet do not.
The shape and hardness /stifness of a shoe heel material can change the kinematics so that force vectors change direction. A stiff heel may have a shape that allows bending of the material which can attenuate the force more gradually than compression of the material or the material may grip the ground and produce more horizontal force vectors from the total GRF available. This is why one parameter such as force attenuation may not be sufficient to give useful information about shock attenuation in terms of reduced internal stress.

quote
"Any intelligent clinician will advise their patients to modify their work activities or even change jobs if conventional measures of reducing the tissue stresses on the injured structural components of the foot and/or lower extremity have failed. However, the surfaces we walk on are not the cause of most foot and lower extremity pathology, as David likes to often suggest. In fact, I propose that the surfaces we walk on in today's society may help prevent ankle sprains, reduce the incidence of falls, prevent puncture wounds to the plantar foot and allow easier access to healthy activities such as bike riding, in-line skating and running than if we all lived in a totally natural environment as our early ancestors did."

Yes I like that, there are so many variables to consider.
Tissue stress and engineering mechanics based evaluation of foot pathology is definentely the way forward and I have found lately that STJ neutral theory is loosing its grip on my thinking. Its strange how early training weaves its way into one's phsyce and is hard to shake off.
I had a guy round today to introduce him to the Amfit system. He was a shoe maker but explaining things in term of tissue stress and mechanics just seemed to make sense to him. The premise is very simple in fact.

Cheers Dave Smith

 

Athletic footwear: unsafe due to perceptual illusions.

Robbins SE, Gouw GJ.
Med Sci Sports Exerc. 1991 Feb;23(2):217-24

Athletic footwear affects balance in men
S Robbins, E Waked, GJ Gouw, J McClaran - British Journal of Sports Medicine, 1994

Seems to me, that it all may be a bit more than just the surface

 

...assuming that Robbins & Gouw are correct in their analysis. I think they have done some good research, but leaped to big conclusions and "editorialised" their results for "sensationalism".

 

Dave (not meaning to patronise) but you're missing the point. The point being that modern man wears this kind of footwear whereas our ancestors did not. So addressing the "hard" aspect of the hard flat surfaces, what you seem to be saying and agreeing with is that our barefoot ancestors were in effect having more force applied to their feet than modern man.

[QOUTE= David Smith] As far as I know not many people live on *frozen lakes and sun baked desert and maybe the one's that did (*in the ice age for instance) had a high prevelance of foot pathology. Unless of course they all wore Nike trainers but more likely they wore some sort of protection from the cold, which as well as being insulating was no doubt 'shock absorbing'.

 

Fellow biomechanists

In the 10,000 year history of shoes (as we would recognise them) there is absolutley no evidence to support their existance has altered anitomical form or function of the foot. Again I stand to be corrected but ground reaction forces on the foot, naked or otherwise, is precisely the same. Whilst shock and pressure may be altered through the material interphase, the value if GRF remains the same.

Cameron

 

What I have done is take one constant (the orthosis and posting helps the foot to function a little more in STJ-neutral - you can witness this quite easily in an over-pronating foot), and satisfied myself that this is at least one thing we can be fairly sure (not certain, mind you) that an orthosis does.
Each new theory as to how an orthosis works or how it helps a particular condition may have it's own merits - I don't dispute that, but I can't see how anyone can understand podiatric biomech if they don't understand what, in broad terms, an orthosis does.

 

Respectfully,
davidh

 

Simon,
If you take points out of context they become meaningless, amusing perhaps, but meaningless.
To put this particular point into context, we don't know the incidence of foot problems back then, nor life expectancy (although that would clearly be far shorter than ours in the West today).
If I walked on dried-up lake bed for a while I would certainly expect lower limb symptoms. If I did it for years I would expect my limbs to adapt to the terrain (not genetically, just my limbs in that body. My children would be normal .

The lower limb was built to enable rapid ambulation over a variety of surfaces.
We can demonstrate this today in a healthy subject. If you check out the lower limb fossil bones of homo erectus, they are much the same as our own.
Our bodies can also adapt somewhat, given time, within one lifetime, to a particular terrain, or occupation. To any constant repetitive force in fact.
I believe this is what happens to many of our patient's feet. but sometimes not until the have crossed the mythical line between "middle-age" and "old-age".

 

You suprise me. But if this is taken into account in Pod Biomech research I'm delighted.

Little suprised that no one mentioned this when I brought it up before on this forum .

 

Then David Holland replied:

Here are a few reasons why I don't necessarily think "that our subtalar joints were built to work around neutral."

1. Most human feet work well and remain asymptomatic for years and possibly their whole lives being pronated from the subtalar joint (STJ) neutral.

2. The neutral position as defined by Root et al is only one of the midrange rotational positions of the STJ possible (with many other midrange rotational positions of the STJ being possible) for normal and asymptomatic function.

3. Optimal gait function is more likely to occur in a foot that stands with a normal STJ axis spatial location than in a foot that stands in STJ neutral position.

4. Many patients that stand in the STJ neutral position have pathology caused by excessive STJ supination moments (i.e. peroneal tendinitis/tendinosus and lateral ankle instability). The patients with the most normal gait function are generally slightly pronated from STJ neutral position in relaxed bipedal stance. Bill Orien, DPM, or Root, Orien and Weed fame, has agreed with me on this point in a conversation I had with him at a seminar about 5 years ago.

5. There is no research to date that shows that patients that function in STJ neutral are less symptomatic. In fact, a gait study of 50 asymptomatic adults by McPoil and Cornwall in 1994 (McPoil TG, Cornwall MW: The relationship between subtalar joint neutral position and rearfoot motion during walking. Foot Ankle Intl., 15:141-145, 1994) seem to indicate that the STJ neutral position is used very little during gait with most function occuring around the rotational position of the STJ seen in relaxed bipedal stance.

Now, for the third time, I would appreciate it if you could answer my question: Why do you think that the foot should function around the STJ neutral position? Please, do not provide an answer such as "because that is what Mert Root said", since that is not going to be sufficient. Also it would greatly help your case if you could provide us with some research evidence that supports your contention that "our STJs are built to work around neutral."

 

David...for what it's worth, I think there is a great deal of merit in the broad consideration of the idea that the human organism is operating well outside the parameters of it's existence over the vast sweep of evolutionary time. In other words we did not evolve for the environment we now live in. The biggest factor in my mind is service life.....lots of feet last 30-40 years pretty well.....but after that performance starts to be pretty sub-optimal in lots of cases....it's just that we don't get eaten by something faster these days....in America they just retire to Florida and eat take away food.....in Aus we just hang about and go to sport stadiums in large flocks. You are not the only believer in the general idea....the whole reductionist double blind study thing clouds some people ability to consider some ideas.....
I have any number of n=1 studies to show that orthoses help sometimes.......and I don't ever expect to find that one shape, theory, material, paradigm, etc will ever work for everybody....after all I only see patients one at a time and as long as they are happy I don't have to "prove" what I do to anybody. I do need to have the courage to admit it when I probably can't help though....which I'm happy to do at times.
I hope you don't feel too ganged up on.....there's few enough people prepared to stick their heads above the trenches as it is....teams of duck shooters tend to make ducks nervous etc...
regards Phill Carter

 

Phill,
You said:
"David...for what it's worth, I think there is a great deal of merit in the broad consideration of the idea that the human organism is operating well outside the parameters of it's existence over the vast sweep of evolutionary time. In other words we did not evolve for the environment we now live in. The biggest factor in my mind is service life.....lots of feet last 30-40 years pretty well.....but after that performance starts to be pretty sub-optimal in lots of cases....it's just that we don't get eaten by something faster these days....in America they just retire to Florida and eat take away food.....in Aus we just hang about and go to sport stadiums in large flocks. You are not the only believer in the general idea....the whole reductionist double blind study thing clouds some people ability to consider some ideas.....
I have any number of n=1 studies to show that orthoses help sometimes.......and I don't ever expect to find that one shape, theory, material, paradigm, etc will ever work for everybody....after all I only see patients one at a time and as long as they are happy I don't have to "prove" what I do to anybody. I do need to have the courage to admit it when I probably can't help though....which I'm happy to do at times.
I hope you don't feel too ganged up on.....there's few enough people prepared to stick their heads above the trenches as it is....teams of duck shooters tend to make ducks nervous etc..."

Very well put, and thanks for the support.
Cheers,
davidh

 

Kevin,
You said:
"Now, for the third time, I would appreciate it if you could answer my question: Why do you think that the foot should function around the STJ neutral position? Please, do not provide an answer such as "because that is what Mert Root said", since that is not going to be sufficient. Also it would greatly help your case if you could provide us with some research evidence that supports your contention that "our STJs are built to work around neutral."

Dr Root et al suggested the axes of motion of the STJ in their 1966 paper Axis of motion of the subtalar joint, and indeed, brought these to the attention of the Podiatry profesion at large. Their experiment was not original however, both Hicks and Manter having done similar, earlier work. But in 1969 Isman and Inman carried out a similar but larger study and found much the same orientations of the axes of motion of the STJ.
So I'm happy with that aspect of Dr Root's work. I BTW wouldn't use the name of an authority figure to back up or validate my contention that the STJ works around neutral.

Here are my thoughts on the matter.
Any joint (the STJ included), by working around neutral is allowed maximum freedom of movement/ROM in each body plane. I think this is reasonably indisputable?
However the STJ, when placed in neutral, ensures that the foot inverts. The foot then has to compensate for the hard and flat surfaces, which is why we see pronated feet in normal, asymptomatic subjects.

I'm sorry to say there appears to be no robust research evidence to support this. Similarly, I see no evidence to suggest the contrary. Results of experiments such as McPoils, of course, can be easily explained by the para above.

 

There is a parallel discussion taking place on thatfootsite on this subject. As usual the majority of posts are not particularly relevant, but the following is an interesting contribution.

 

Simon,
You said:
"But I thought you said that we didn't evolve to walk on hard flat surfaces? If our ancestors were walking and evolving in these environments, why didn't selective pressures/ factors contribute to the adaptation?"

Are you seriously comparing dried-up river beds to pavements?

The hominid/human lower limb is a superb adaptor. It adapts so well mainly because of the ROM within the STJ. Speaking from personal experience (having buggered my ankle several weeks ago and been wading in rocky rivers last week) I can tell you that when the STJ ROM is compromised it puts enormous strain on other areas of the body. But not, strangely, when walking on pavements.


Quote:
Originally Posted by Davidh
The lower limb was built to enable rapid ambulation over a variety of surfaces.
We can demonstrate this today in a healthy subject. If you check out the lower limb fossil bones of homo erectus, they are much the same as our own.


You then said:
"
But only yesterday you said the fossil record was to scarce to draw any conclusions, now you seem perfectly happy to draw conclusions from it. So perhaps you could tell me how similar the articular facets of ther STJ are between the species and suggest how this is changing with evolution..."

I'm not aware of any robust studies which puport to show this. I haven't done any myself.
It's perfectly true that the hominid fossil record is sparse. However I would have thought that a single specimen (Turkana Boy/homo erectus) from 1.6 million years, who possessed much the same osseous makeup in his lower limbs as we do today, would at least make you curious as to how this could be. Not robust scientific evidence as such but certainly it should make us all query the postulate that we have adapted for life on a hard, flat surface rather suddenly That would be in hundreds of years (rather than tens of thousands, or millions).
Cheers,
davidh

 

And David Holland replied:

Is this your answer??....because by working around neutral that maximum freedom of movement in each body plane is allowed?? This is not only disputable but obviously wrong even to those podiatrists who consider themselves Root disciples. Root et al claimed that STJ neutral position was the rotational position of the STJ where the foot had twice as much supination as pronation motion (i.e. 2:1). From this calculation, then the rotational position of the STJ that "allows maximum freedom of movement in each body plane" would be 3-5 degrees supinated from the STJ neutral position, depending on the range of motion of the joint. Since your argument above of "maximum freedom of movement in each body plane is allowed" is obviously wrong by Root et al's definition and since you don't have any research, let alone "robust research", to back up your claim that the foot should function around the STJ neutral position, then I'm afraid, David, that you have not provided us with anything solid to rest your case on.

In reading the string at ThatFootSite that Mark Russell so helpfully pointed out to us, it made me take a step back and think about how my passion in debating important points for the podiatric profession may give the wrong impression to other podiatrists reading along. As I have said numerous times, I was, at one time, a "Root disciple". I attended many of Mert's yearly seminars, had "arguments" with him during his seminars, and learned a great deal from the man. In addition, I had two classes taught by John Weed, worked with him personally on a "Biomechanics Workbook" for 2nd year podiatry students, spent a week in his private practice in San Jose, and had many long discussions with him during my Biomechanics Fellowship. I also had many discussions with Bill Orien and was trained in "Root biomechanics" for 5 years by the Podiatric Biomechanics Faculty at the California College of Podiatric Medicine. I greatly respect these men and what they did for podiatry and did for me personally, because without the foundations and inspiration that they provided for me, I would certainly never have been able to understand biomechanics of the foot and lower extremity at my current level.

However, in my observations and research over the years, I have come to conclude that certain assumptions Root, Weed and Orien made and taught over the years were simply not true. And one of these assumptions that I disagree with is that the ideal functioning rotational position of the STJ for each is the STJ neutral position. I believe that as long as the patient stands in relaxed bipedal stance in a position that is not maximally pronated at the STJ and is at least 2-4 degrees supinated from the maximally pronated position in relaxed bipedal stance that they have potential to have optimal gait function. However, if the patient stands in the maximally pronated position, then it is very unlikely that they will be able to have optimal gait function. In other words, I don't believe that feet need to stand in STJ neutral position or function in STJ neutral position to have optimal function and be asymptomatic.

Feet must not be too close to the maximally pronated STJ position in standing since this leaves too little range of motion during the contact phase of gait to allow the foot to undergo adequate pronation motion, which is an important shock-absorbing mechanism of the human locomotor apparatus during walking and running. Now this may not seem to be an important point to many, but I think it is critically important when we start to try to understand why injuries are produced in the human foot and lower extremity and that these injuries may not simply be due to "the foot not functioning around the STJ neutral position" as David Holland and many other Root disciples suggest. Until we start to better appreciate these fine details of how the rotational position of the STJ and spatial location of the STJ axis affect the production of injury in the foot and lower extremity, we will not have the clinical effectiveness for our patients that we could have had, if we had only understood this important pedal joint more thoroughly.

 

I'm pointing out flaws in your theory David by demonstrating that hard and flat surfaces are not a new thing. This builds on the argumewnts I have already put forward which also deconstruct your theory.

I thought you said it was the inability to adapt to hard flat surfaces that was the source of pathology? Now you are saying it is a superb adaptor?
Actually, in the grand scheme of things the human being is a relatively poor adaptor.

So now you're saying that walking on pavements is good for you. I'm sorry David but I'm rapidly loosing interest in this topic as you twist and turn and change your mind continuously.


One final thought on this. I wish everyone would stop talking about how the foot evolved as a past tense, once happened, now finished situation. Evolution is still happening.

 

I think there is a big difference from those who are invited to speak on a topic at conference in recognition of the achievements and knowledge by the organisers and those who set up their own courses and talk tripe for financial gain, having no qualification to do so. Which is how this discussion began.

 

Simon,

I really have no problem with David and Ian setting up a course to try to educate podiatrists on biomechanics of the foot and lower extremity and treatment with foot orthoses. It is very hard work organizing and speaking at a conference and, if I was going to do it, I would also want to be paid for my work. I see this as no different than me charging my patients for foot orthoses, office visits, injections or surgery since they are paying for my expertise and I am gaining financially for it, much as David and Ian are also gaining financially for organizing and lecturing at their courses. In fact, I congratulate them on taking on this responsibility since I think that since foot biomechanics is so poorly understood by many podiatrists, having a conference on foot biomechanics would help many podiatrists become better clinicians.

I have no problem with David personally and have enjoyed his many contributions to these lists in the past. My only problem is his continued insistence that hard, flat surfaces are at the root of most of the foot and lower extremity pathology we all see on a daily basis. As I have said before, it is a factor, but only one of very many and probably it is a minor one next to increased body weight, physical activity level, poor shoegear, poor biomechanics, and the effect of ageing on tissue mechanics and on the central nervous system.

However, I am still having a whole lot of fun arguing my side of the case against STJ neutral position theory. In fact, probably haven't had this much fun since I argued the definition of STJ neutral with Chip Southerland and Jeff Root about 5 years ago on the Podiatry Mailbase.

 

Conferences on foot biomechanics are fine Kevin, I'm personally planning a lecture series on why I believe the world is flat and hard. I guess you are right though, at the end of the day people will either attend and make up their own minds or vote with their feet. Trouble is if you attend to find out its rubbish...

[QOUTE= Kevin Kirby]I have no problem with David personally and have enjoyed his many contributions to these lists in the past. My only problem is his continued insistence that hard, flat surfaces are at the root of most of the foot and lower extremity pathology we all see on a daily basis. [/QUOTE]

Agreed. Never met him. Don't agree with his theory though. This is what academic debate is. To the casual observer it may seem that we dislike each other as individuals, when in reality we just disagree with each other at an intellectual level.

So on that note, I'll step in to try and help David out. The reason why the foot is better off functioning around it's mid-range is because in this position there is the net least tissue stress about the joint. Unfortunately, this is unlikely to be at the neutral position of the joint as described by earlier workers, but rather some degree's inverted. However, while there will be a point of least stress, there will be an area of low stress; this low stress zone (i'm calling this after myself BTW), so Spooner's low stress zone may well have the STJ neutral position within it.


Have a nice day- I think I'm becoming American

 

Simon,
Have to agree here
I remember having a discussion with you in our long and distant past regarding this!!
However, I distinctly remember it being a zone of tolerance
The key is not whether someone functions around neutral etc, but whether they are operating within their zone of tolerance. This is of course determined by a number of factors, as Kevin has alluded to.
Operating around "neutral" may be one of them, although I question how long during gait the STjt is functioning around neutral
When that zone of tolerance is exceeded either acutely (major) or due to minor repetitive trauma , associated pathology follows.
It is also important to remember that the zone is not a constant due to age age etc, thereby, why we are unable to continue functioning at the same level. Forces etc. that are being applied, may be constant, but our ability to cope with them is not!!
cheers
Tony

 

So its either the Spooner Low Stress Zone or the Achilles Zone of Tolerance??

Simon, I'm also feeling a little bit like I need to help Dave Holland out here with his side of the argument as to why injuries may occur with walking over hard, flat surfaces. It isn't necessarily that the foot is functioning more pronated from neutral because of the hard, flat surfaces. As for flat surfaces, it is the increased repetitive nature of the exact same magnitude of stress and strain on certain structural components of the foot and lower extremity (i.e. ligaments, tendon, cartilage, bone, muscle, tendon) with each step that likely causes the injury.

In other words, walking on a flat surface would tend to cause the same magnitude of stress and the same strain rate at one or more of the structural components of the foot and/or lower extremity with each and every step. In addition, the flat surface would also tend to focus those abnormal stresses and strains on a very limited number of structural components so that they would tend to accumulate an abnormal amount of stress and strain over and over again with each step. This would tend to lead to degeneration of the specific structural components of the foot and/or lower extremity due to either fatigue or due to the tissue being subjected to stresses farther along on its stress-strain curve, away from its elastic range and into its plastic range where permanent deformation or tissue damage (i.e. microscopic cellular damage, partial or complete tissue tears, and stress fracture) may occur.

Compare this to walking over an undulating or uneven surface where the tissue stresses would tend to change anatomical locations with each step and the magnitude of stress and magnitude of strain rate would change at these tissues with each step. This would tend to possibly allow the stressed tissue to have more time interval to recover back to its pre-strain level of length with, let's say, an every 3rd or 4th step time interval, rather than a one step time interval.

Hard surfaces would tend to cause problems, like Dave Smith stated, due to shock-related phenomena that are probably completely independent of those effects caused by long hours of walking on level surfaces. However, we must realize that the injury that the individual develops from walking on hard surfaces may not be directly caused by the increased externally generated force transient that acts on a certain tissue which, in turn, was caused by the mass of the foot and lower extremity striking the hard surface with a certain contact velocity. Instead, it is important to realize that the injury may be caused by compensation for the anticipated shock by the individual's central nervous system modulating muscle preactivation and realigning the joint angles of the foot and lower extremity in preparation for contact with a hard surface.

Much of the research by Benno Nigg's group at the University of Calgary over the past 10-20 years has been focused on studying this "muscle tuning" that will occur with the foot being subjected to different shoes, foot orthoses and surfaces while running. Here is a very small list of Benno Nigg's and this group's research. (Nigg, B.M., Barry Karr. Biomechanical Aspects of Sport Shoes and Playing Surfaces, The University of Calgary, Calgary,1983; Nigg, B.M. (ed.). Biomechanics of Running Shoes, Human Kinetics Publishers, Inc., Champaign, Illinois, 1986; Nigg, B.M.: The assessment of loads acting on the locomotor system in running and other sports activities. Seminars in Orthopaedics, 3 : (4) 197-206, 1988; Nigg BM: The role of impact forces and foot pronation: a new paradigm. Clin J Sport Med, 11:2-9, 2001; Mundermann, A., B.M. Nigg, R.N. Humble and D.J. Stefanyshyn: Orthotic comfort is related to kinematics, kinetics, and EMG in recreational runners. Med Sci Sports Exercise, 35:1710-1719, 2003; Mundermann A, Wakeling JM, Nigg BM, Humble RN, Stefanyshyn DJ: Foot orthoses affect frequency components of muscle activity in the lower extremity. Gait and Posture, 23:295-302, 2006.)

Some of the earliest and most fascinating soft surface-hard surface running kinematics research was done on individuals who were made to run on surfaces ranging to ultra-soft, pillow-like compliant surfaces to surfaces that were hard and stiff. This research was done in the late 1970s by Tom McMahon, who made his fame co-developing a "tuned indoor track" at Harvard http://www.news.harvard.edu/gazette/1999/02.18/mcmahon.html. This "tuned track" that he constructed allowed runners to shave 7-8 seconds off their mile times and cut running injuries by half by matching the stiffness (i.e. compliance) of the track's surface with the measured stiffness of the runner's lower extremities. The following sources are required reading for anyone interested in this subject (McMahon, T.A. and P.R. Greene: The influence of track compliance on running. J. Biomechanics, 12:893-904, 1979; McMahon, T.A.: Muscles, Reflexes and Locomotion. Princeton University Press, Princeton, New Jersey, 1984).

I'll be very content, thank you, if we just assume that the injuries that sometimes occur with walking or running on hard, flat surfaces are not caused by the foot being pronated from STJ neutral, and are more likely caused by the mechanisms I describe above.

 

Fellow biomechanics

Back to walking on terra firma. The pendulum action of the rearfoot in conjunction with locking mechanism of the forefoot to rearoot would give the multiarticular segmented leg optimal leverage during closed chain, shoes (and foot orthoses) would have little effect e.g. feet continue to pronate over the surface of wedged inlays anyway. However something wihich is critical to the debate of evolution and that is the low angle of toe clearance. There is some evidence this has reduced over time but something that might be seen to destablise the COM, in modern bipeds has remained virtually the same from the beginning of time, which would indicate the mechanism of walking per se has little to do with the surface we walk over.

Cameron .

 

Thanks, everyone, for a very interesting debate.

I want to make a couple of final points, if I may.
To Simon.
You alluded several times during this thead to qualifications, or lack of them for teaching purposes. Not only have I guest-lectured at Durham School of Podiatry, but I was also offered Associate Lectureship at APU (I turned it down). These don't mean much, but with these offers and my undergrad and post-grad degrees I think I'm at least as well-placed to teach as many lecturers in UK Pod Schools? You also mentionedQuality Control/Assurance.
These terms can mean much or little. I see for example that the Alliance/Midlands School who train FHPs have Quality Assurance in place.
As to teaching itself. Well, we offer to re-tread anyone who didn't get it first time around (at our expense).
We give email clinical support (unlimited) for anyone who needs it, again, at our expense.
And we have the ability to "buy in" guest lecturers, as and when needed.

Spooners low stress zone would seem to be described already, in Nordin and Frankels Basic Biomech of the Musculoskeletal System - page 308 (in the 2nd Ed) see the defn for Neutral axis.
Anyway, thanks for your time and contributions.

To Kevin.
I think Dr Root and colleagues made a big contribution to Podiatry, and I envy your meeting and being taught by him, even if you subsequently realised that some of the theory did not fit in with what is actually happening (maybe our thoughts are not too far removed after all?).
The 2:1 ratio of inversion/eversion becomes relatively meaningless when we start the foot off in an inverted position, as I contend it will go into when placed in STJ-neutral. If we can accept that for at least some of the time (on an undulating or soft surface) the foot will contact the ground inverted (and stay that way though mid-stance to toe-off) then the STJ would, after all, be working around neutral.

Sincere thanks for pointing out the work we are trying to do in the UK.
At the end of the day we teach people how to find STJ-neutral, how to cast, how to prescribe and what conditions can be helped with orthoses. Since we aren't "flogging" a product-line or belief-system, we underpin our teaching with some basic science, so duirnal variation, cardinal body-planes, the windlass mechanism and some anatomy and physiology revision are introduced also.

Regards,
davidh

 

l think you'll find that UK Universities insist that their teaching staff undergo formal teaching qualifications.

I was being facetious David

 

Me too

On the subject of UK teaching quals, I found this from Sunderland Uni (where I did my 1st degree).
"You will possess higher education learning and teaching expertise and a professional qualification in sports medicine, physiotherapy, podiatry or a similar profession allied to medicine. In addition you should have a higher degree in a related subject area."
I have these quals - would they take me on do you think?

At the end of the day though I agree with you. Lecturing to degree-standard requires the necessary quals, and I've no doubt that Sunderland Uni would tack on a teaching qual at some stage.
Thanks for participating.
Cheers,
davidh

 

Curious to know why you might think the human foot is still evolving......are there selection pressures removing part of the gene pool before reproduction....that are changing the frequency of allelles in the total pool ....?...sounds like you may be an expert here...can you explain the claim to a pleb like me?
regards Phill Carter

 

David:

If you just forgot about STJ neutral in your explanation as to why hard, flat surfaces may be a problem for some individuals, then you would be on much more hard, flat, and secure ground with your explanation.

 

There are several reasons why evolution is not a finite thing.

Firstly, mutation.

Secondly, we don't mate assortively

Thirdly, gene linkages

I'm sure there are more reasons but this is just off the top of my head.

Phil, can I ask why you think evolution has ended? And moreover, where is this finite theory of evolution being taught?

 

In the Vatican City

 

BTW as I said previously, don't consider myself an expert.

 

Good call Javier

 

Doesn't hysteresis alter the tissues stiffness? Would this also mean that we don't have the "exact same magnitude of stress and strain"? Also with repetitive cycles would we not see changes in muscular contraction due to fatigue leading to changes in kinematics and/ or kinetics? This then also has the potential to alter loading rates, leading to variation in tissue stiffness due to visco-elasticity and thus, alteration to the stress strain characteristics?

This seems to contradict with the "body being a sense organ" as you expand upon below. Surely the body is monitoring and varying to avoid such injury. Perhaps this is one of the reasons we have so much built in redundancy? Also, the flat surface should limit extremes of joint motion. Given the tissue stress paradigm, this should be a good thing. As you pointed out yourself- less inversion injuries etc.

If only we walked on flat surfaces- Haven't all day. And I have been checking.

See my comments above. Would be interesting to do some sensory deprivation experiments here.

Do you think this work is applicable to walking or just running?

I am interested in the 'cut running injuries by half statement"; how was this evaluated?

Also, perhaps one of the better physicists could tell me how reducing the track stiffness would effect loading rate of the tissues?

Anyway, I've had my nike pegasus on again today, so no hard surfaces for me.

 

I should not have written "exact same magnitude of stress and strain" since I meant to say "approximately the same" with hard, flat surfaces versus "a lot of variation" with uneven surfaces. I don't know the answers to all your other question other than hysteresis is more a measure related to the energy loss to heat from the loading-unloading cycle of a structure and is not a direct measure of stiffness/compliance.

I don't think there is necessarily a contradiction since many repetitive stress injuries are not "compensated" for by the CNS since the CNS is not aware of the impending injury that is gradually occuring until the tissue is damaged (e.g. metatarsal stress fracture). If the CNS, though, somehow senses that injury may occur (e.g. from a prior painful experience) then gait compensation due to changing muscle firing patterns may occur.

Don't know.

Don't know.

Even though I haven't read McMahon's research for some time, I believe he explained that if the track was pushed downward and then recoiled upward at the same rate that the human lower extremity did during running that he could "have the track do some of the work" for the muscles and improve speed. The "cut injuries by half" was taken off the webpage, and I know nothing more about it. Probably you can disregard it since it is likely to be anecdotal information and not from a scientific study.

From seeing all your questions, maybe it is time for you to go back to your Low Stress Zone again, Dr. Spooner.

 

Hysterisis
It is a description of the effect seen in the change in the loading unloading curve of a material. Most non-biological construction materials do not suffer this but visco elastic materials do.
The effect is seen by graphing the stress/strain (load/length) curve. So a material is loaded to a certain force FY and the strain (change in length) is X+6 the load is released to zero but the strain/length does not return to zero. Let’s say this new resting length is X+1. The loading unloading cycle is repeated and the resting length is X+2. One can see from this that if the 2nd loading cycle starts at X+2 then, if the strain is linear, at the third load cycle of FY, length = (X+2) + Strain (change in length) X6 = X+8.
For Tendon tissue this effect of hysterisis last for about 6 – 10 cycles and then the stress strain curve becomes linear. This is called pre-stressing after this stress strain curve is closer to that of non-biological materials and it is in this state that tendon and ligament is usually tested for the purposes of characterising stiffness etc.

The pre-stressed stress /strain curve of some biological materials like tendon and plantar fascia tend to be non-linear. This is because of the make up of the tissue, which consists of collagen, which is very stiff and elastic tissue, which is less stiff, plus the collagen is laid in wavy coils about the elastic tissue. This means that low loads can equal larger stress/ strain ratios than high loading levels.

The problem with calculating at what limb position will cause a certain strain is that the muscle can contract to take up the strain and protect the joint. If this does not happen then the ligaments may be over stressed and the strain may cause damage to them.
The way in which this occurs is down to the CNS, I would imagine, and may be variable from person to person. But it is my understanding that the muscle tends to protect the joint from excursion outside its physiological RoM and avoid damage to ligaments and capsule.
So for this reason I would seem reasonable to say that it would be unreliable to characterise tendency for muscle strain in terms of limb position.
As ligament relies only on its elasticity and stiffness to apply its passive action it may be reasonable to predict ligament trauma in terms of limb position.
As ligament is stiffer with mainly collagen fibres its stress strain ratio is much smaller in that large stress produces small strains. This, I think, would mean that ligaments would have a more definable pathological RoM than tendon.

Simon, You coined the phrased “Spooners Stress free zone” this may have been tongue in cheek but I think this is a excellent ‘sound bite’ that encapsulates the concept of tissue stress in terms of joint RoM. The stress free zone may be variable inter and intra subject and activity but, would you agree, it is a goal that we should be trying to achieve as clinicians in terms of resolution and prevention of chronic or acute trauma.

The track stiffness tuning may be to do with harmonics ( I’m only guessing).
Harmonics is something that engineers try to avoid. This is where the input and resonance frequencies of the energy from applied force and the structure are harmonic ie the same or multiples of the same frequency. When this occurs large resonance and deflections can occur in a structure and leads to failure.
So if a track was tuned to the same harmonics as the energy transfer frequency thru the body segments then the returned energy could be in harmony and so increase deflection ie upward and forward projection. Its difficult to see how this might be tuned for each individual athlete but perhaps energy transfer is fairly uniform thru the body inter subject.
Divers do this when they adjust the board to spring back in tune with their own style and body. Also try jumping on a trampoline with several other people. The trampoline does not harmonise with your bounce and you cannot get very high ie less deflection because the energy is not returned in the right direction or at the right time.

Cheers Dave Smith

 

Here's a good explanation of harmonics from http://physics.mtsu.edu/~wmr/shm.htm which yo will need to go to if you wish to see the animations.


Simple Harmonic Motion and Resonance
Motion that repeats in a regular pattern over and over again is called periodic motion. As we will come to appreciate, periodic motion is crucial to the production of musical tones. However, to begin our analysis we look at the most basic type of periodic motion called simple harmonic motion. Simple harmonic motion occurs in a myriad of different forms in the everyday world; for example, a person bouncing on the end of a diving board, a child in a swing, or your cousin's funky car (you know the one with no shocks) that bounces down the road like a low-rider every time you hit a bump.

Physicists like simple harmonic motion (let's begin abbreviating it SHM) because every example of SHM is based on the same underlying physical principle and all examples of SHM have the same, very straightforward, mathematical description.

What is the physical principle? SHM occurs around an equilibrium position when a mass is subject to a linear restoring force. A linear restoring force is one that gets progressively larger with diplacement from the equilibrium position. The best example of this is a spring. The more you stretch a spring the larger the force trying to get the spring back to its original shape.

What is the simple mathematical form of SHM motion? The displacement of the oscillating mass varies sinusoidally (whoa, big word!) as a function of time. [sinusoidal means like a sine function. You remember sine and cosine functions from your trig classes don't you?]. We won't do too much with the formula but here it is:

y = A sin(2pf t)









What you do need to know is the meaning of the symbols in the formula and be able to identify these parameters in different examples of SHM. Below is a animated image that shows how the displacement of a simple harmonic oscillator varies with time. Warning! I made the image myself and I am no Walt Disney animator. It is supposed to represent a mass on a rubber band or spring and the graph on the right plots the position, y, as a function of time, t, along the x-axis.







Here are the definitions of the parameters relevant to SHM:

Amplitude, A. The amplitude of the oscillation is the maximum distance that the oscillating object moves away from the equilibrium position. That last phrase is very important. Many people make the mistake of taking the peak-to-peak amplitude of the sinusoidal oscillation. Nope! it is only the distance from the center to one extreme. So in the figure above the amplitude of the oscillation is 1 (that is the distance from the equilibrium position at 0 out to the extreme of the motion at 1 on the graph).

Frequency, f. The frequency of the oscillation is the number of oscillations per second. Remember an oscillation is one complete cycle of the oscillator.

Period, T. The period is the time for the oscillator to complete one cycle. It should not be a big stretch to figure out that the frequency and period are related (actually they are just different ways of expressing the same information).

f = 1/T
The key feature of SHM is that the period or frequency of the motion does not depend on the amplitude of the oscillation. In other words whether I set a mass on a spring oscillating with a large amplitude oscillation or a small amplitude oscillation the period of the SHM remains the same and it depends only on the physical structure of the oscillator. From a practical viewpoint this effect was used to make the first accurate clocks. A pendulum takes the same time to make one oscillation even though the amplitude of the oscillations dies down with time. The period does not change.

Resonance

Resonance is another vital concept in acoustics. We will discuss resonance in much more detail in class but here is a simple description for an everyday simple harmonic oscillator system--a child in a swing. For any given length of the chain of the swing there is a corresponding natural period of oscillation. (Surprisingly, the period of oscillation does not depend on the mass of the person sitting in the swing.) When we push a person in a swing we instinctively give them energy exactly at the natural frequency of oscillation because we only give a push when the swing is just past its maximum amplitude and moving away from us. Even though we are only giving the swing small pushes, the amplitude of oscillation of the swing grows rapidly. We are said to be driving the oscillator at its resonant frequency. If we instead chose to push the swing at a much higher frequency we would be pushing at a variety of different points in the swing cycle. At some of those times the swing would be moving towards us while we are pushing away thus we would be counteracting the growth in amplitude of the swing. The net result is that the same number of equal sized small pushes would just make the swing move erratically in a small region around the equilibrium position. This jerky erratic motion can, of course, really tick off the swingee! The net result is that if we input even a small amount of energy into a SHM oscillator at its natural frequency of oscillation the result is large amplitude oscillations.

Damping

Damping is the term used to describe the loss of energy with each cycle of a simple harmonic oscillator. The simple harmonic oscillator begins with a certain amount of energy, for example when we compress or stretch the spring attached to a mass. In an ideal simple harmonic oscillator this energy would remain the same forever. Note that the energy converts between kinetic energy (energy associated with a moving mass) and potential energy (energy stored in a non-moving form such as that stored in a stretched or compressed spring). In the real world, the mechanical energy of the simple harmonic oscillator is always lost to heat due to air resistance or friction in a bearing or in a spring. For a lightly damped simple harmonic oscillator the fraction of energy lost each cycle is small and shows up as a slight reduction in the amplitude on each successive oscillation. However, as we said above the period does not change even in this lightly damped case