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Do “cushioning” shoes really cushion impacts?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Paulo Silva, Sep 10, 2007.

  1. Paulo Silva

    Paulo Silva Active Member


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    Hello

    I'm following the thread What do we mean by 'motion control' in running shoes and I remembered this:

    Most athletic shoes companies advertise injury protection through “cushioning.”

    But some studies suggest that shoes with cushioning materials fail to absorb impact when humans run and jump, and actually amplify force under certain conditions...

    I would like to hear your opinions... on this
     
    Last edited by a moderator: Sep 14, 2007
  2. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    The cynic in me thinks this about cushioning - when the heel hits the ground, the knee flexes; the ankle flexes; the STJ pronates; the CoM drops; -- these are all impact moderating behaviours; and then there is the plantar heel fat pad --> so, the body is pretty good at absorbing shock itself ---- any cushioning in the shoe only has the potential to absorb some of what is left over .... how much is left over? I don't know, but it may not be much.
     
  3. Admin2

    Admin2 Administrator Staff Member

  4. Cameron

    Cameron Well-Known Member

    Paulo

    >Most athletic shoes companies advertise injury protection through “cushioning.”

    I have always taken that to mean cushioning by absorbtion through cellular materials traditionally used in shoes prior to the introduction of no cellular polymers and visco elastics. I would be very suspicious of any claims to reduce injury by this means.

    > But some studies suggest that shoes with cushioning materials fail to absorb impact when humans run and jump, and actually amplify force under certain conditions...

    I think this relates to shock attentuation (and not cushioning) and was specifically found in shoes with viscoelastic materials additions (either as inlays or inserts.

    toeslayer
     
  5. I've attached a couple of papers which explore some of these issues. The first paper explores some of the methodological problems. The second really explains what we have been talking about in the previous threads. Enjoy.
     

    Attached Files:

  6. Paulo Silva

    Paulo Silva Active Member

    Hi

    Craig Payne

    I liked your view:)

    toeslayer

    Good point about cellular polymers and visco elastics.

    Sorry, English its only one of my 3 not mother tong spoken languages, can you please explain this better?:eek:

    Simon Spooner

    Tanks for the info, what is your point of view on this?
     

  7. "Shoe cushioning" is the lay-public word for the shock absorbing midsoles of certain styles of shoes. Whether the midsole is ethylene vinyl acetate (EVA), polyurethane (PU), air, gel or springs, the idea is to allow a force on the midsole to allow deformation of the midsole to occur to absorb the impact of the foot hitting the ground during running.

    Basically the idea is that the shoe midsole will be able to contribute toward the deceleration of the center of mass of the body toward the ground during the first half of the support phase of running gait. As Craig said, the human body has other, more important, shock-absorption methods including hip flexion, knee flexion, ankle joint dorsiflexion, subtalar joint pronation and longitudinal arch flattending during the first half of support phase to help "cushion" the impact of the foot landing on the ground during running.

    Shoes can help absorb some of the impact forces of running, but only if the shoe cushioning is "tuned" for the individual's weight and running style. Too soft of a shoe midsole will bottom out quickly, causing more shock in a heavy runner. Too hard of a shoe midsole in a lighter runner, will not deform enough to maximize shock absorption. Shoe cushioning must, therefore, be tuned for the runner for optimum comfort and injury prevention. Unfortunately, sometimes, this is a trial and error process from a clinical standpoint. The clinician needs to have a good knowledge of both shoe biomechanics and running biomechanics to be able to help runner-patients find their optimal shoe for training and racing.
     
    Last edited: Sep 12, 2007
  8. Great papers, Simon.:) Hope everyone that treats runners as patients reads these papers.
     
  9. Caleb Wegener

    Caleb Wegener Welcome New Poster

    Cushioning does not reduce the vertical ground reaction force but rather increases the time taken for the initial ground reaction force peak to occur. This is an important function as it does give the body more time to adapt to the forces being applied. The greatest way to alter the size of the initial force peak is a change in running kinematics.

    Cushioning does reduce high plantar pressures which have been shown to be associated with increased levels of foot pain in people with pes cavus (Burns et al., 2005). I have attached a paper that I presented at the ISB Footwear Symposium in Taipei. It showed large reductions in plantar pressure by neutral running shoes in athletes with a cavus foot type. However the patterns of pressure reduction differed significantly between shoes examined.
     

    Attached Files:

  10. Cameron

    Cameron Well-Known Member

    Paulo

    >Sorry, English its only one of my 3 not mother tong spoken languages, can you please explain this better?

    Shock is a general term for impact and attentuation relates to measured amplitude when combined the phrase, ' shock attenuation ' describes properties of material which affect the magnitude (size) of impact force.

    Cushioning is a term used to described physical ways of reducing peak pressures.

    I would concur with Caleb's explanation.

    toeslayer
     
  11. But since the tissues are visco-elastic the slower rate of loading means that the tissues are less stiff and can store less energy as a result.
     
  12. Glad you enjoyed them- more on this in San Diego!
     
  13. Paulo,

    I didn't attach the two papers for nothing! Read these and you will understand my view on this.
     
  14. Paulo Silva

    Paulo Silva Active Member

    Tank you all for the comments and information it was very helpful.:)

    Simon (I did read the paper's, about 4 times:eek:)
    Kevin ( I agree with the tunning its very important but sometimes forgotten)
    toeslayer (tanks)
    Caleb Wegener (great papper)


    I know I'm just a shoe fitter but reading your posts has been very enrichment for me.


    Do you realize that in the retail, the average runner and even some health professionals think "cushioning" or shock absorbing as probably the only feature to look for wen buying athletic shoes (we see it every sale the customer itself or by any recommendation (magazine, health professional, friend, etc) asks about the cushioning ability of that particular shoe.

    Even brand's "experts" wen go to retail or public talking about the shoes, their main focus usually its the cushion their brand particular technology provides.

    I try to focus on Fit myself, but it's hard wen all around people speak another language::rolleyes:
     
  15. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    Your insight is an enrichment for us!
    I recall the first mutters about "shock absorbtion/cushioning" perhaps not being all its cranked up to be first appearing >20 yrs ago! At the ISB Footwear Biomechanics conferences, this has been in mainstream scientific thought for some time now.....the problem is as long as magazines like Runners World continue to talk about it and rate shoes based on it and runners continue to be smart and read about it, the problem will remain.
     
  16. toomoon

    toomoon Well-Known Member

    oh oh.. it's me again.. a very interesting break off thread.

    Gee I may as well stick with my terminology beef and say I think we are talking shock attenuation and not shock absorbtion! T

    The big problem, as Caleb has pointed out is that the perception is that cushioning lessens impact peaks.. ie the 1st Fz peak, which it does not. Cushioning has a big eddect on pressue and shock, but an arguable effect on Fz impact peak occuring at about 50ms

    The Kerdok paper is a very important one.. and brings to light the effect of viewing the lower limb as a spring hich may bemore or less compliant.

    The issue with midsole hardness... and its supposed abilit to cushion, relates to its effect on this compliance.
    This is very complex, because the brain identifies surface hardness instantly, and through altered muscle action, changes lower limb stiffness.

    I have attached a few more papers for your reading pleasure

    Maybe the term use by Kevin.. tuning.. needs a little more definition.. is it in relation to muscle preactivation.. as a learned or "hard-wired" response to surface and impact.. or is it a biofeedback loop which alters at every step in response to surface hardness.. the adidas 1 was based on this premise.

    good discussion though

    regards to all
    Simon
     

    Attached Files:

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