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Do shock absorbing insoles in recruits undertaking high levels of physical activity reduce lower limb injury? A randomized controlled trial.
J R Soc Med. 2006 Jan;99(1):32-7

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The results in the above study are somewhat at odds with previous studies that showed the opposite.

Karl Landorf had a commentary published with the above paper:
Shock absorbing insoles and lower limb injury. Karl B Landorf. Royal Society of Medicine (Great Britain). Journal of the Royal Society of Medicine. London: Jan 2006. Vol. 99, Iss. 1; p. 3

Here is an excerpt:

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Craig Payne
Department of Podiatry
La Trobe University
Melbourne, Australia
http://www.latrobe.edu.au/podiatry
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God put me on this earth to accomplish a certain number of things - right now I am so far behind, I will never die.
The views expressed above are those of the author and not that of La Trobe University
This is where I am, where are you?

Craig,

Can I throw this one in for good measure.

Sherman et al, JAPMA, Vol 86, No. 3, March 1996.

"Prevention of Lower Limb Pain in Soldiers using Shock-Absorbing Orthotic Inserts"

38% of soldiers issued inserts had lower limb problems
29% of soldiers with lower limb pains did not have inserts.

Main Conclusion, shock attenuation did not reduce lower leg pain in recruited soldiers.

Kind Regards,

for me there are too many variables on this randomized trial

type of trainer being used because in UK the standard issue trainer is normally Hi tec Silver shadow which has no support plus standard issue boots which they are made to exercise in are not the greatest for reducing injuries.

What they should have done is incuded a group that had specialised running trainer for there feet plus shock absobing insole and see what the results would be with that

chris

I would have thought the opposite was the case. As it was a military population all variables (eg footwear; activity level; etc) were controlled for. The only variable of interest and the one manipulated was the shock absorbing insoles.

Does Shoe Insole Modification Prevent Stress Fractures? A Systematic Review.
Snyder RA, Deangelis JP, Koester MC, Spindler KP, Dunn WR.
HSS J. 2009 Jun 9. [Epub ahead of print]

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All

First of all what do we mean by shock absorption? I prefer to call it shock attenuation, which is a more precise description.

Interestingly the paper attached makes the distinction between shock attenuation and cushioning. Where shock attenuation is the increase in time for the exchange of energy between two bodies and specifically anything that reduces the magnitude of the forces in the lower limb and their joints. For Cushioning it is that part of foot gear that reduces the magnitude of the peak of the initial heel strike force, which they call the heel strike transient (HST). Both are really shock or force attenuation since the force peak (amplitude) is reduced and the force time (frequency) is extended.

Now first, what if the HST is an essential part of the bodies ability to predict the hardness of the ground at the time of impact for that step. The signal generated by the HST is detected and analysed by the central nervous system and allows it to alter the shock attenuation properties of the whole body.

If the cushioning added to the foot by shoe or insole etc reduces the HST then the CNS processing may interpret this as soft ground and adjust the shock attenuation appropriately I.E. The attenuation potential would be less and so the force amplitude would be higher. This may lead to forces in the lower limbs that are above the optimal or maximal limit of non pathological locomotion.

Second It seems unlikely that cushioning would significantly change the shock attenuation for the whole body.

Imagine a heavy mass, say a block of stone of say 100kg, and attached to that stone is a large spring. Drop the stone from 1metre high onto a force plate so that it lands on the spring and the accelerations or GRF are characterised for analysis.
Now do the same with a 3mm piece of poron over the force plate. I can't imagine that the force impulse would change much i.e. the force amplitude and frequency levels would be very similar. The attenuating or damping effect of the poron is many times less then the spring and this mismatch of damping frequencies results in insignificant change. If the poron was much thicker then the frequencies would have a close ratio and so the effect would be far greater.


Consider natural terrain, I can't think of any surface that has a very thin soft covering over a hard surface. This is what a shoe does, it gives a false perception of the surface hardness or more closely the stiffness in terms of bulk modulus (deformation under uniform pressure).

This is before we consider the effects a shoe with a deep heel and sole has on the moments about the foot joints when compared to a bare foot.

Perhaps then, a shoe with a thin fairly resilient sole would be better than a thick soft heel and sole. The foot, while protected from sharp objects, would get a better early warning about the true ground stiffness properties and moments about the joints would be similar to bare foot.

Even if you had a shoe heel and sole which was deep enough and with the properties to significantly attenuate force to the body, like a Judo mat for instance, then the problems of weight, moments about the foot joints and energy return would still exist and make ambulation problematic and probably traumatic.

What are your thoughts on the above?

Dave

Attached Files

ShockAtten.doc (1.25 MB, 8 views)

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Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.

Dave, you should read Robbins and Gouw: http://www.ncbi.nlm.nih.gov/pubmed/2...?holding=ukpmc
Also:http://www.ncbi.nlm.nih.gov/pubmed/2893969
Robbins has written much on shock attenuation, athletic footwear, balance etc.- google him.

I know Craig has some problems with the Robbins-Gouw hypothesis, or at least with their research ... Craig?

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Further to my reply above. This is a topic that has fascinated me for some time. On the one hand we have research which seems to suggest to much "cushioning" is bad, on the other hand we have research which suggests that a "tuned" surface stiffness can have positive effects- see McMahon and other advocates. Mcmahon's tuned surfaces in terms of their stiffnesses are more akin to the judo mat than the tarmac or the african plains, or the perma-frost wastes or many other of the surfaces we allegedly evolved to walk upon.

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Hi

I have just finshed my 3rd year as a student and for my dissertation, i looked at the differences in pressure using trainers for different foot types (so a cushioned shoe, motion controlled shoe and structured cushioned shoe) using a neutral foot type, and the results were intresting that the expensive trainer re distributed the pressure worst. I will not go into it now as it is going off topic, happy to answer any questions though.

I know it has no strength as it was a piece of under grad work, however it has made me want to continue the research on.

The main question i have from it though is (after reading some of B, Nigg's work) what is more important to help in injury prevention. Pressure reduction or reduction in muscle activity and do they interlink? and how does this effect say diabetic sports people as pressure reduction is more important for them???

I am sorry for the questions, it the one of the many areas that puzzles me and find it hard to find a answer

Thanks

Nick

Simon, Yes those referenced abstracts appear to have a similar conclusion as my proposition.

Cushioning is a difficult concept to define. Cushioning in the paper attached earlier was that amount of force attenuation that significantly reduced only the heel strike transient force peak (HST) at around 25ms of stance phase. More cushioning than this at first may not significantly effect the force impulse sine wave shape but may significantly alter moments about the ankle joint complex. Large amounts of cushioning will have the ability to change the frequency of the sine wave by attenuating it. However this cushioning alone probably will not have much elasticity and so energy loss is increased. Obviously the ability to build the optimum cushioning and elasticity to augment the optimal force impulse for the activity of interest would be much easier to build into a track than the bottom of a shoe.

Now my Kangoo Jump boots http://kangoojumps.com/ are an excellent example of attenuation and elastic return. The deep springs have the ability to have large deformations under stress but also store the energy to return for the propulsive stage of running. This gives excellent protection from high force amplitude induced injuries and enables me to run at similar speeds to normal joggers. The ski boot style upper boot and the wide sole to road interface stops the huge moment potentially developed during running on uneven surfaces from breaking my ankles (which is good).
However while great for fun running and keeping fiit they would never allow you to win a marathon or a sprint race since the energy return is quite slow and each boot weighs about 2kg. That makes a lot of inertia to deal with swinging on the end of your leg. A track surface designed to give the same frequency energy return would negate this weight / inertia problem and the excessive moment problem, while still maintaining the low force amplitude benefits.

Cheers Dave

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Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.

Nick

In your experiment how was the pressure of interest defined and characterised?
Do you have an abstract and conclusion we can look at?

Reduce internal forces by changing the application of external forces in some way.

Pressure is still force but characterised over an area. It can be very difficult to reduce the total force applied to the foot for a certain activity, however we can change the point of application or spread the application over a greater area and reduce local or discreet force application.

One way to reduce total force applied but maintain velocity is to walk with shorter steps with increased cadence.

Hope this helps

Dave

Dave

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Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.

McMahon had a go at this...

How's your knowledge of the physics of cone springs, Dave?

Attached Files

Mcmahon patent.pdf (984.3 KB, 3 views)

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Hi Nick,

This is an area that has interested me for a long time as well. I was asked to do a Chapter on computerized gait analysis back in the 1990's. (In Valmassey's text on the biomechanics of the lower extremity.) It was quite an educational experience. It was interesting, not only in studying the available technology, but looking at what practioners wanted from the technology. Doctor's wanted a test to tell them what's wrong the patient and what they should do. They want a simple number to look at e.g. peak force. However, it is not that simple.

Whether pressure or muscle force is more important is determined by the tissue in question. For example, a skin ulcer under the hallux. Reducing the contact pressure at the hallux will be important in healing that ulcer. There are many factors that determine the pressure under the hallux, but it seems obvious that pressure or pressure time integral is probably going to be the bottom line.

On the other hand, in posterior tibial dysfunction I would bet that muscle force is going to be more important than pressure under the foot. Or more precisely thate muscle force demanded by the activity. You could make the case for center of pressure under the foot, and its relation to the STJ axis, will be very important in PT dysfunction.

What writing that chapter helped me understand is that you can make a lot of measurements, but they won't be useful unless you can correlate them with pathology. Sometimes it's even more helpful to go beyond correlation to causation. I feel that this is where it is helpful to think like an engineer and try to explain foot pathology with the tissue stress approach.

Keep up the research,

Eric

Dave please find abstract below

Abstract
Background
Since the ‘running boom’ in the 1970’s running shoe design and the technologies used have been on the increase. Now there are three types of shoe to fit different foot types. Wearing incorrect foot wear may cause injury, and the correct may prevent injury. There is a constant supply of research for this area, with the results often contradicting each other and new paradigms being proposed.

Objective
The objective was to use a single participant, with a neutral foot type, to determine whether there was a significant difference between three different types of Asics running shoe and a plimsoll, in plantar pressure under the 1st MTPJ. Also the centre of trajectory line was compared.

Method
The participant was carefully selected, and the foot posture index was used to identify the participant had a neutral foot type. The study was conducted on a treadmill, using the F-Scan to capture the data. ANOVA test was the statistical test used to analyse the results with some visual analysis, using SPSS version 15.




Results
A significant difference (p value < 0.05) between the plimsoll and the three shoes was found. A positive effect of the centre of trajectory was noticed in the all the three shoes compared to the plimsoll.

Conclusion
The study set out to look at whether there was a difference in plantar pressure in a neutral foot type. The Asics trainers do reduce pressure compared to the plimsoll. The best shoe for this purpose based on this experiment’s findings was the Asics Gel Foundation shoe, which is the mid range priced shoe agreeing with (R, Clinghan et.al, 2007) that they redistribute more effectively. Moreover the Gel Foundation was the shoe designed for the heavily pronated foot type. All the shoes redistributed the plantar pressure under the 1st MTPJ area more effectively than the Plimsoll. The Gel Nimbus was the least effective at pressure redistribution out of all the shoes for the neutral foot type.

So the null hypothesis was rejected and the alternative hypothesis was taken up.

However, a definitive conclusion cannot be made as to which shoe is the best shoe for the neutral foot type. In the literature review some research on pressure redistribution has suggested that it is not always the key factor; rather muscular activity is a key factor in injury prevention. (B, Nigg, 2001) Plantar pressure cannot be ignored. For example, it is important to redistribute pressure for a diabetic person. This area of research is a very complicated one and more research is required.

The one conclusion that can be drawn is that the Asics Gel Nimbus, Gel Foundation and GT shoes all work better than a plimsoll for a neutral foot type in redistributing pressure and controlling the foot.



Please don't be too harsh, was a hard project


Eric,

Thank you, that is what i thought, in the fact that you apply it to the pt in front of you.


Nick

Nothing specific but I can have a read up.

Dave

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Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.

good study, definitive results :-)