Podcast 72: Neuroplasticity, EVA Shoe Foam, and Shoe Trends

Maximalist shoes and the death of Minimalism ? Could this be true ?

*Show sponsor: www.newbalancechicago.com

Lems Shoes.  www.lemsshoes.comMention GAIT15 at check out for a 15% discount through August 31st, 2014.

A. Link to our server: 

http://traffic.libsyn.com/thegaitguys/pod_73f.mp3

Direct Download: 

http://thegaitguys.libsyn.com/podcast-72

B. iTunes link:

https://itunes.apple.com/us/podcast/the-gait-guys-podcast/id559864138

C. Gait Guys online /download store (National Shoe Fit Certification and more !) :

http://store.payloadz.com/results/results.aspx?m=80204

D. other web based Gait Guys lectures:

www.onlinece.com   type in Dr. Waerlop or Dr. Allen,  ”Biomechanics”

______________

Today’s Show notes:

1. Neuroplasticity: Your Brain’s Amazing Ability to Form New Habits
new link (does not have the old photo ivo mentioned that he loved)
 
2. Last week we pounded the sand on EVA foam and maximalist shoes. There was alot of attention, emails and good social media discussion on the topic.  
LETS REVIEW IT
file:///Users/admin/Downloads/p142_Heel_shoe_interactions_and_EVA_foam_f_web_150dpi.pdf
 
3. Then there just last week there was an article in LER on “the death of minimalist shoes” ? 
READ THIS: 
The rise and fall of minimalist footwear | Lower Extremity Review Magazine
http://lermagazine.com/cover_story/the-rise-and-fall-of-minimalist-footwear
 

4.  Physical Therapy as Effective as Surgery for Meniscal Tear

Kathleen Louden

March 20, 2013
Torn Meniscus? Thinking about surgery? Think again…


5. Cast study: the broken foot tripod

Podcast 72: Neuroplasticity, EVA Shoe Foam, and Shoe Trends

Maximalist shoes and the death of Minimalism ? Could this be true ?

*Show sponsor: www.newbalancechicago.com

Lems Shoes.  www.lemsshoes.comMention GAIT15 at check out for a 15% discount through August 31st, 2014.

A. Link to our server: 

http://traffic.libsyn.com/thegaitguys/pod_73f.mp3

Direct Download: 

http://thegaitguys.libsyn.com/podcast-72

B. iTunes link:

https://itunes.apple.com/us/podcast/the-gait-guys-podcast/id559864138

C. Gait Guys online /download store (National Shoe Fit Certification and more !) :

http://store.payloadz.com/results/results.aspx?m=80204

D. other web based Gait Guys lectures:

www.onlinece.com   type in Dr. Waerlop or Dr. Allen,  ”Biomechanics”

______________

Today’s Show notes:

1. Neuroplasticity: Your Brain’s Amazing Ability to Form New Habits
new link (does not have the old photo ivo mentioned that he loved)
 
2. Last week we pounded the sand on EVA foam and maximalist shoes. There was alot of attention, emails and good social media discussion on the topic.  
LETS REVIEW IT
file:///Users/admin/Downloads/p142_Heel_shoe_interactions_and_EVA_foam_f_web_150dpi.pdf
 
3. Then there just last week there was an article in LER on “the death of minimalist shoes” ? 
READ THIS: 
The rise and fall of minimalist footwear | Lower Extremity Review Magazine
http://lermagazine.com/cover_story/the-rise-and-fall-of-minimalist-footwear
 

4.  Physical Therapy as Effective as Surgery for Meniscal Tear

Kathleen Louden

March 20, 2013
Torn Meniscus? Thinking about surgery? Think again…


5. Cast study: the broken foot tripod

Here is a great case from a reader.

“Hey guys, I absolutely love the show, especially as it becomes less and less over my head.

Due to your love of gait-altering absurdly thick EVA midsoles, I thought you might like to check out this Hoka incident that occurred at the Marathon des Sable across the Sahara in Morocco, a 6 day 251km event. It was posted by Ian Corless at Talk Ultra Podcast. Apparently the medial side of the midsole collapsed—on DAY 2! This guy finished the race, and as you have to carry 100% of your gear and nutrition, I guess he only had the one pair. It looks like this runner should fly out to CO or IL asap, because if he didn’t have gait issues before, he is sure to have them now.”

This brings up some scary thoughts when it comes to the amount of EVA foam and quality of foam (EVA or otherwise) being used in some shoes.  ”The more foam there exists, the greater one can break down into their compensation or deforming strategy.” What do we mean by this ?  Well, two things should be on one’s mind:  1. all foam breaks down into the vector of the deforming forces and 2. most of us do not have perfectly clean biomechanics, thus an abnormal loading vector is most likely present. These aberrant biomechanics are eventually reflected into our shoes as a “wear pattern”.  In this case, the EVA foam had progressively broken down into their rearfoot pronation (and likely mid and forefoot pronation). In this case, even if the person had enough tibialis posterior and other medial pronation-decelerating structure strength at the start, the acceleration of their foot into this issue is now even more abrupt, brisk, excessive etc.  A new pair of shoes would not be broken down into this deformity and so a newer pair of shoes is preventive. This is why we recommend new shoes often, and the cycling in of another pair (or several pair) into the mix so that one is never driving the same shoes into the potentially destructive compensation patterns that most of us  have.  At least with a fresh pair of shoes brought into the mix at the 200 mile wear point, you would only be in the more destructive shoes every other run, giving the body time to recuperate more. 

As for this pair of shoes, this runner either has a terrible right foot problem or this was a brutally flawed right shoe from the get go, or both. We can only imaging how painful the medial knee might be at this point.  Furthermore, imagine the abrupt nature of the hip internal rotation mechanics ! IF they do not have hip labrum impingement yet, they will soon !  And with that amount of internal limb spin, can you imagine how inhibited the glutes would be from constantly having to eccentrically control that excessive rotation? 

As a whole, are not huge fans of the HOKA shoe family, we just cannot fathom the need for this much foam under the feet. If you have been with us long enough you will have heard on our podcast and blog talk about increased impact forces with increasing EVA foam thickness (want that info, here is the link and references). Just because some EVA foam is good, doesn’t mean more is better.  Remember, to propulse off of a foam infrastructure you must bottom out/compress the foam sufficiently to find a firmness to propulse from. The Hoka’s have plenty of foam making this our concern, and we are not picking on just them. There are other companies doing this “super sizing/super stacking” such as Brooks, Altra, and New Balance to name just a few.  Sure they have added a greater forefoot rocker/toe spring on the front of the shoe to help (they have to because the foam thickness is so great that there is no flexing of the forefoot of the shoes), but is it enough for you? Remember, every biomechanical phase of the gait cycle is necessary and timely to engage the natural joint, ligament, muscle components of joint loading, mobility, stability and movement. If you spend too much time in one phase (perhaps because you are waiting for foam to decompress) you may wait a moment too long and miss the opportunity for another critical phase to begin in the sequence.  This is the root cause of many injuries, aberrant biomechanics leading to aberrant mobility or stability. 

So remember these few things:

1. more is not always better for you, it may be for some, but maybe not you.

2. there is a price to pay somewhere in the mechanical system, after all the body is a contained system. What doesn’t happen at one joint often has to be made up at the next proximal or distal joint.

3. Everyone has some aberrant mechanics. No one is perfect. These imperfections will reflect in your shoes, and the longer you are in a pair of shoes the deeper the aberrant mechanics will be reflected in your shoe, thus acting as a steering wheel for the aberrant pattern (the steering is more direct/ more aggressive than in a new pair of shoes). So keep at least 2 pair of shoes rotating in your run cycle, one newer and one half done. We even recommend 3 pairs often.  Trust us, the sudden biomechanical shift from a dead shoe into a new one (even though it is a clean new shoe without bad patterns in it) is still a biomechanical shift and could cause adaptive phase problems, pain or injury.

Lots to consider in this game. It is not just about dropping into barefoot and taking off down your street. Not if you want to be doing this for a long time and stay healthy.

Shawn and Ivo, the gait guys

* next day follow up from our social media pages:

Along the lines of EVA and yesterdays post: 

“Wear of the EVA consistently increased heel pad stresses, and reduced EVA thickness was the most influential factor, e.g., for a 50% reduction in thickness, peak heel pad stress increased by 19%. “

This study looks at a model; it would be interesting to see this study with a large cohort.

Biomed Mater Eng. 2006;16(5):289-99.

Role of EVA viscoelastic properties in the protective performance of a sport shoe: computational studies.

Even-Tzur N1, Weisz E, Hirsch-Falk Y, Gefen A.

http://www.ncbi.nlm.nih.gov/pubmed/17075164

More on EVA foam, impact loading behaviors, and adding shoe inserts.

A few weeks ago we wrote about some thoughts on the maximalist shoe foam trend and how it is possible that more foam could mean alterations in impact loading behaviors that could lead to problems (note we used the word could, and not will).  If there are pre-existing proprioceptive deficits in a limb these issues most likely will rise to the surface. 

The EVA foam in shoes is primarily used to absorb forces via air flow through interconnected air cells in the EVA during shoe deformation under body-weight. When the shoe has seen a finite number of compressive cycles the air cells collapse and the EVA can compact on itself leaving the shoe with an negatively impacting area of compression to fall into.  Shock absorption may be impacted and possibly lead to injury.

The Robbins study we discussed a few weeks ago (link) suggested that the reduction of impact moderating behaviour is 

Reduction of impact-moderating behavior is a response to loss of stability induced by soft-soled cushioned shoes: Humans reduce impact-moderating behavior in direct relation to increased instability.This is presumably an attempt to achieve equilibrium by obtaining a stable, rigid support base through compression of sole materials. Humans reduce impact-moderating behavior, thereby amplifying impact, when they are convinced that they are well protected by the footwear they are wearing. 

These were important points but we wanted to bring to your awareness of the component of the shoe you may have not thought of to this point, the foam foot bed that comes with the shoe, or ones you might add to the shoe  yourself post-purchase. With what we have just taught you in our last blog post and this blog post, we will let you make the connection we are suggesting you be aware of when it come to more foam, changes in foam as the shoes and inserts degrade and impaired impact loading behaviors.

There are just 3 brief study summaries here, take the time to read them and read between the lines now that we have educated you a little better in how to think about them.

Shawn and Ivo

J Appl Biomech. 2007 May;23(2):119-27.

Effects of insoles and additional shock absorption foam on the cushioning properties of sport shoes.

The purpose of this study was to investigate the effects of insoles and additional shock absorption foam on the cushioning properties of various sport shoes with an impact testing method. 

The results of this study seemed to show that the insole or additional shock absorption foam could perform its shock absorption effect well for the shoes with limited midsole cushioning. 

Further, our findings showed that insoles absorbed more, even up to 24-32% of impact energy under low impact energy. 

It seemed to indicate that insoles play a more important role in cushioning properties of sport shoes under a low impact energy condition.

_______

Biomed Mater Eng. 2006;16(5):289-99.

Role of EVA viscoelastic properties in the protective performance of a sport shoe: computational studies.

 Using lumped system and finite element models, we studied heel pad stresses and strains during heel-strike in running, considering the viscoelastic constitutive behavior of both the heel pad and EVA midsole. In particular, we simulated wear cases of the EVA, manifested in the modeling by reduced foam thickness, increased elastic stiffness, and shorter stress relaxation with respect to new shoe conditions. Simulations showed that heel pad stresses and strains were sensitive to viscous damping of the EVAWear of the EVA consistently increased heel pad stresses, and reduced EVA thickness was the most influential factor, e.g., for a 50% reduction in thickness, peak heel pad stress increased by 19%. We conclude that modeling of the heel-shoe interaction should consider the viscoelastic properties of the tissue and shoe components, and the age of the studied shoe.

________________

J Biomech. 2004 Sep;37(9):1379-86.

Heel-shoe interactions and the durability of EVA foam running-shoe midsoles.

A finite element analysis (FEA) was made of the stress distribution in the heelpad and a running shoe midsole, using heelpad properties deduced from published force-deflection data, and measured foam properties. The heelpad has a lower initial shear modulus than the foam (100 vs. 1050 kPa), but a higher bulk modulus. The heelpad is more non-linear, with a higher Ogden strain energy function exponent than the foam (30 vs. 4). Measurements of plantar pressure distribution in running shoes confirmed the FEA. The peak plantar pressure increased on average by 100% after 500 km run. Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foamreduces heelstrike cushioning, and is a possible cause of running injuries.

 

More on EVA foam, impact loading behaviors, and adding shoe inserts.

A few weeks ago we wrote about some thoughts on the maximalist shoe foam trend and how it is possible that more foam could mean alterations in impact loading behaviors that could lead to problems (note we used the word could, and not will).  If there are pre-existing proprioceptive deficits in a limb these issues most likely will rise to the surface. 

The EVA foam in shoes is primarily used to absorb forces via air flow through interconnected air cells in the EVA during shoe deformation under body-weight. When the shoe has seen a finite number of compressive cycles the air cells collapse and the EVA can compact on itself leaving the shoe with an negatively impacting area of compression to fall into.  Shock absorption may be impacted and possibly lead to injury.

The Robbins study we discussed a few weeks ago (link) suggested that the reduction of impact moderating behaviour is 

Reduction of impact-moderating behavior is a response to loss of stability induced by soft-soled cushioned shoes: Humans reduce impact-moderating behavior in direct relation to increased instability.This is presumably an attempt to achieve equilibrium by obtaining a stable, rigid support base through compression of sole materials. Humans reduce impact-moderating behavior, thereby amplifying impact, when they are convinced that they are well protected by the footwear they are wearing. 

These were important points but we wanted to bring to your awareness of the component of the shoe you may have not thought of to this point, the foam foot bed that comes with the shoe, or ones you might add to the shoe  yourself post-purchase. With what we have just taught you in our last blog post and this blog post, we will let you make the connection we are suggesting you be aware of when it come to more foam, changes in foam as the shoes and inserts degrade and impaired impact loading behaviors.

There are just 3 brief study summaries here, take the time to read them and read between the lines now that we have educated you a little better in how to think about them.

Shawn and Ivo

J Appl Biomech. 2007 May;23(2):119-27.

Effects of insoles and additional shock absorption foam on the cushioning properties of sport shoes.

The purpose of this study was to investigate the effects of insoles and additional shock absorption foam on the cushioning properties of various sport shoes with an impact testing method. 

The results of this study seemed to show that the insole or additional shock absorption foam could perform its shock absorption effect well for the shoes with limited midsole cushioning. 

Further, our findings showed that insoles absorbed more, even up to 24-32% of impact energy under low impact energy. 

It seemed to indicate that insoles play a more important role in cushioning properties of sport shoes under a low impact energy condition.

_______

Biomed Mater Eng. 2006;16(5):289-99.

Role of EVA viscoelastic properties in the protective performance of a sport shoe: computational studies.

 Using lumped system and finite element models, we studied heel pad stresses and strains during heel-strike in running, considering the viscoelastic constitutive behavior of both the heel pad and EVA midsole. In particular, we simulated wear cases of the EVA, manifested in the modeling by reduced foam thickness, increased elastic stiffness, and shorter stress relaxation with respect to new shoe conditions. Simulations showed that heel pad stresses and strains were sensitive to viscous damping of the EVAWear of the EVA consistently increased heel pad stresses, and reduced EVA thickness was the most influential factor, e.g., for a 50% reduction in thickness, peak heel pad stress increased by 19%. We conclude that modeling of the heel-shoe interaction should consider the viscoelastic properties of the tissue and shoe components, and the age of the studied shoe.

________________

J Biomech. 2004 Sep;37(9):1379-86.

Heel-shoe interactions and the durability of EVA foam running-shoe midsoles.

A finite element analysis (FEA) was made of the stress distribution in the heelpad and a running shoe midsole, using heelpad properties deduced from published force-deflection data, and measured foam properties. The heelpad has a lower initial shear modulus than the foam (100 vs. 1050 kPa), but a higher bulk modulus. The heelpad is more non-linear, with a higher Ogden strain energy function exponent than the foam (30 vs. 4). Measurements of plantar pressure distribution in running shoes confirmed the FEA. The peak plantar pressure increased on average by 100% after 500 km run. Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foamreduces heelstrike cushioning, and is a possible cause of running injuries.

 

More shoe foam may mean more problems.

Last night we had a great online teleseminar (www.onlinece.com). The talk was minimialism. Here was 2 of our take home points:

More foam in the shoe is not always good.

“Shoes with cushioning fail to absorb impact when humans run and jump, and amplify force under certain conditions, because soft materials used as interfaces between the foot and support surface elicit a predictable reduction in impact-moderating behavior. ” -Robbins

Basically barefoot feet, and even shoes with thinner foam/soled shoes, tend to judge impact more precisely because there is less foam to dampen proprioceptive input. The more foam you stack under the foot, the more material that must be deformed before a sufficiently rigid surface can be detected by the foot. Think of this, what do we do in rehab ? We stand people on stacked foam to give them an unstable surface (if they have championed balance challenges on a stable surface first, this is an important first step). When the foot cannot find a firm platform it searches for stability and drowns in the instability. This can be what more foam under the foot provides, inability to reference stable ground surface can negatively impact proprioceptive joint and tissue receptors.

2. Impact loading behaviors.

if we know the surface (the shoe or the actual surface/ground) is unstable, we will modify the pending impact loading behavior. In other words, you will jump differently onto a frozen puddle than you would dry ground. Studies have shown that the more foam a shoe has (ie. the more the potential instability from the example above) the greater the reduction of impact moderating behavior.

Humans reduce impact-moderating behavior in direct relation to increased instability.- Robbins

hope to see you in the next online teleseminar in 4 weeks !

shawn and ivo

reference:

BioMechanics April 1998 

Materials: Do soft soles improve running shoes?
Most athletic shoes advertise injury protection through “cushioning,” but real world studies have not shown impact moderation.
By Steven Robbins, MD, Edward Waked, PhD, and Gad Saad, PhD

You create your own gait problems.

Just a simple reminder. Most shoes have EVA foam between the hard outsole rubber. EVA foam compresses but it also has memory. If you have a running form issue or a foot type that drives abnormal biomechanics into the shoe then over time the shoe’s EVA foam will break down into that pattern. Not only does this then support the problem, but it enables you to engrain the pattern (which means you are not engraining a cleaner pattern) meaining that every other joint and muscle then assumes that this is the norm and begins to alter their function based on the premise. A sign issue can drive many issues and many other complaints.  This client had a rigid rear foot varus , obviously as you can see by the wear pattern (yes, we gently and lovingly flogged this running for wearing the shoes this long into this pattern) but it was made worse by letting the shoe entrench this pattern so deeply. You see, their rear foot varus was no where nearly as bad as the wear into this shoe. But they continued to wear it and the foam continued to break down further and deeper into this varus wedged pattern. They came into see us for lateral knee pain and a tight IT band that was not responding to foam rolling (we immediately began to whimper and then proceeded to thump our forehead into our desk, repeatedly).  Some things should be obvious, but even we are far from perfect or wise at times.  

Key point, you have heard this here over and over again from us, have 2 or 3 pairs of shoes. Introduce the new shoe into your running repertoire at the 200 mile mark. At that point start rotating your shoes so that you are only a day away from a newer shoe that his not broken down into a faulty pattern and thus deformed EVA foam.  Even by the time the one shoe is dead and done, you have not been in it every run.  You should never kill a shoe to the 500 mile mark and then buy a new shoe. The pattern you have worn into your shoe will suddenly disappear when you put on the new shoe. Injuries occur from repeated events or sudden changes. Reduce your risk and rotated at least 2 pairs of shoes, one newer and one older.  

We talk about alot of these issues, and so much more, in the National Shoe Fit Certification Program. Email us if you think you might be interested.   thegaitguys@gmail.com

And ……when it comes to your feet and shoes, use your head.

Shawn and Ivo, The Gait Guys