FOOTBEDS: THE UNKNOWN COST OF SUPPORTING THE ARCH OF A SKIER’S FOOT


Two recent studies (1.), (2.) question the merits of supporting the arch of a skier’s foot and especially any claims made that supporting the arch in neutral is the strongest position for skiing. 

It is well established in the scientific literature that the plantar aponeurosis (aka plantar fascia or PA) is one of the major arch-supporting structures of the human foot.  A positive correlation between Achilles tendon loading (ATF) and plantar fascia tension (PAF) has been reported. A study (3.) found that plantar aponeurosis forces (PAF) gradually increased during mid stance and peaked in late mid stance. The study found a good correlation between plantar aponeurosis tension (APF) and Achilles tendon force (ATF). The study concluded:

The plantar aponeurosis transmits large forces between the hindfoot and forefoot during the (mid) stance  phase of gait. The varying pattern of plantar aponeurosis force (PAF) and its relationship to Achilles tendon force (ATF) demonstrates the importance of analyzing the function of the plantar aponeurosis throughout the stance phase of the gait cycle rather than in a static standing position. – (my emphasis added in bold)

I discussed this in my post TRANSITIONING TO A HIGHER LEVEL OF SKIER PERFORMANCE.

The graphic below from Kevin Kirby’s Foot and Lower Extremity Biomechanics II:  Precision Intricast Newsletters, 1997-2002 illustrates how the position of COM in relation to the foot tensions the GS (gastroc-Soleus) compressing the arch which tensions the plantar aponeurosis ligament. I have added arrows to indicate PA strain Force F and Shear Force as well as Arch Compression Force.

The graphic below also from Kevin Kirby’s Foot and Lower Extremity Biomechanics II:  Precision Intricast Newsletters, 1997-2002 illustrates how the anterior (forward) advance of CoM in relation to the foot decreases rear foot loading (GRF-RF) and increases fore foot loading (GRF-FF). I have added a red dashed vertical line and a red triangle to show the approximate location of what would be what I term the tipping or pivot point where the foot would rock rearward and forward with a corresponding shift in CoM.

The two recent studies I referred to (1.), (2.) that question the merits of supporting the arch of a skier’s foot were actually done with subjects walking and running on flat and inclined surfaces. But the effect on arch compression is applicable to the effect of arch supports used in ski boots.

New Balance Minimus road MR00 shoes were provided to all participants to wear for testing (approx. weight 180 grams, zero heel-toe drop, no medial arch support and a uniform EVA midsole). Pockets filled with lead weights were affixed to the laces of both shoes in order to standardize foot weight across all shoe and insole conditions. The minimal shoe was chosen as a control condition in order to standardize non-insole effects as much as possible.

Two separate custom insoles were designed for each participant and fabricated by orthotic laboratory. The first insole was designed to restrict arch compression near-maximally compared to that during shod (barefoot) running (Full Arch Insole; FAI). The second insole was designed to restrict compression by approximately 50% during stance (Half Arch Insole; HAI). TO qualify for the study participants could not wear orthotics on a regular basis.

The study found:

The insert restricted maximum arch compression by approximately 70% when compared to unrestricted shod running and consequentially resulted in lower strain values throughout the entire stance phase. It should be noted that the PLF length only surpasses the estimated resting length between ~25%-80% of the stance phase in the insert condition (Fig 3). The negative strain values should be regarded as a slack PLF length, not as the PLF shortening beyond the resting length. 

The graphic below from the paper The Foot’s Arch and the Energetics of Human Locomotion shows the maximum arch compression of subjects shod barefoot (Shoe-only), with the Half Insole that restricted arch compression to 50% of the maximum amount and with the Full Insole that maximally restricted arch compression. The Full Insole is typical of insoles used to support the arch of a skiers’ foot.

 

The insoles had no effect on the metabolic cost of walking despite restricting ~80% of arch compression. 

In a personal communication with Sarah Stearne she advised me that the study didn’t measure muscle EMG activation with and without the insole but they did know that the ankle performed less positive (-8%) and negative (-10%) mechanical work when the insole was worn and that the ankle peak dorsiflexion moment was reduced (-7%). Based on the ankle moment and Achilles tendon moment arm data they calculated that there was ~6% less force in the Achilles tendon when the insole was worn.

Whilst several studies have acknowledged the elastic energy storage potential of the PLF, this ligament is primarily regarded for its role in providing integrity to the bony arch structure, and in supplying the rigidity required for the foot to function as a lever during propulsion (or skiing, my comment) 

This study confirms what I experienced in 1973 after I had full support custom orthotics made by a well known sports podiatrist. The orthotics felt comfortable standing on them and even walking. I experienced some discomfort when attempting to run with the orthotics in my jogging shoes. But when I tried skiing with them in my ski boots I felt as if my foot were floating on the top of the orthotic with little or no sensation of any force under my first MPJ.

Based on the results of two cited studies I believe there is no basis to assume that supporting the arch of a skier’s feet will have positive benefits or is without adverse consequences without first conducting comparative studies using standardized controlls (no insole, flat boot board) and established scientific protocols.


  1. The Foot’s Arch and the Energetics of Human Locomotion – Sarah M. Stearne1, Kirsty A. McDonald1, Jacqueline A. Alderson1, Ian North2, Charles E. Oxnard3 & Jonas Rubenson1,4 – (January 19, 2016)
  2. The Role of Arch Compression and Metatarsophalangeal Joint Dynamics in Modulating Plantar Fascia Strain in Running – Kirsty A. McDonald1, Sarah M. Stearne1, Jacqueline A. Alderson1, Ian North2, Neville J. Pires1, Jonas Rubenson1,3* – (April 7, 2016)
  3. Dynamic loading of the plantar aponeurosis in walking – Erdemir A, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA

9 comments

  1. Hi David,

    I just received a copy of the (University of) Vermont Quarterly magazine where I found an article under the heading of Physical Therapy in which a clinical associate professor in the Department of Rehabilitation and Movement was observing a pair of thin soled “children’s moccasins” in the campus museum and says “I pictured a child who had a shoe that was comfortable, but less functional. I wondered how this child learned how to walk with less support, especially with uneven terrain at the time”. The professor is also a practicing physical therapist, it is noted.

    He is presuming disfunction when the child probably had stronger more functional feet than most of today’s youths who are wearing arch supported isolation footwear.

    There seems to be a serious disconnect with current research or an unwillingness to accept that the old “foot is weak and must be supported” concept is outmoded and has been debunked by many qualified authorities with the research to back them up. It is especially disturbing to see such old concepts being perpetuated at the university educational level.

    Nordica had an article on their website titled “So, How Should a Ski Boot Fit, Anyway?”. It was interesting to find a footnote at the end of the section on footbeds headed ” Caveat Emptor. While North American skiers have long considered custom footbeds to be essential gear, most Europeans, including racers, continue to regard them as little more than novelty items.” Amazing to see that in an article which, otherwise, promoted the “perfect fit” concept. I don’t know if that article is still up or has been edited and the author spanked for not “toeing” the corporate line which was printed immediately above and below.

    I am interested in reading the footnoted articles above, but a publication source is not listed. Also, is there any source for finding barefoot minded DPMs for functional assessments?

    Regards,
    Herb

    1. Dynamic loading of the plantar aponeurosis in walking – Erdemir A1, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA.- https://www.ncbi.nlm.nih.gov/pubmed/14996881

      The Foot’s Arch and the Energetics of Human Locomotion – https://www.researchgate.net/publication/291164811_The_Foot's_Arch_and_the_Energetics_of_Human_Locomotion

      The Role of Arch Compression and Metatarsophalangeal Joint Dynamics in
      Modulating Plantar Fascia Strain in Running –
      https://www.researchgate.net/publication/299985956_The_Role_of_Arch_Compression_and_Metatarsophalangeal_Joint_Dynamics_in_Modulating_Plantar_Fascia_Strain_in_Running

      Good comments in this new YouTube video about how the focus in footwear is what sells not how it affects the function of the user. In my opinion skiing is dominated by marketers and accountants. – Shoespiracy (Extended cut) – https://youtu.be/x_rDFa6kZfI

      There is a big push in the industry to upsell footbeds and custom fit liners with every sale of a ski boot because these items are a lucrative source of revenue. Footbeds and custom liners probably generate more net profit than the ski boot. It is easy to sell footbeds with simple parlour tricks like asking a customer sit down and look at their feet. Then ask them to stand up and then point out how their arches collapsed under their weight because their feet are weak and not capable of supporting them. Then the salesperson clinches the sale by saying, “Think about what happens in skiing. This is why every skier needs a foundation in the form a footbed”.

      1. Thank you for the references, David, and the video is great and should be must seeing for all, skier or not. It would be nice to see a little more info on the speakers qualifications to lend it more credence for the general public. Seeing Dr. Emily Splitchal is enough for me.

        Yeah, the other sales pitch is the one where the guy says “I wear them in all my shoes and boots all the time”. Mostly because, once your foot adapts to the footbed it can be painful to not wear them or switch back and forth, on and off.

        Regards,
        Herb

      2. Dr. Irene Davis, Director of the Spaulding National Running Center, Spaulding Hospital Cambridge and visiting Professor of Physical Medicine and Rehabilitation, Harvard Medical School, USA

        Prof. Daniel E. Lieberman, Department of Human Evolutionary Biology, Harvard University

        Catherine Willems PhD, Director of Future Footwear Foundation at KASK, School of Arts, Ghent, Belgium

        Dr. Emily Splichal, CEO/Founder Evidence Based Fitness Academy, Podiatrist and Functional movement specialist

        Mike Friton, Innovator and Footwear Designer

        Chris McDougal, Author of Born to Run and Natural Born Heroes

        Charlie Dark, Musician, Yoga Teacher & Founder of Run Dem Crew

        Dr. Rangan Chatterjee, Physician, Bestselling Author, Podcast Host and TV Presenter

        New study just published – Medicine and Science in Sports and Exercise –
        Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles – Sarah T. Ridge; Mark T. Olsen; Dustin A. Bruening; Kevin Jurgensmeier; David Griffin; Irene S. Davis; A. Wayne Johnson – https://www.medscape.com/viewarticle/907333src=wnl_edit_tpal&uac=190975HX&impID=1914288&faf=1

  2. “Whilst several studies have acknowledged the elastic energy storage potential of the PLF, this ligament is primarily regarded for its role in providing integrity to the bony arch structure, and in supplying the rigidity required for the foot to function as a lever during propulsion (or skiing, my comment)”

    What is PLF?

  3. I’m curious here. I have had a couple clients with flat feet in my instructing at Snowmass, CO. They end up overbuckling to gain feel and snugness over the forefoot. Footbeds in both cases allowed them to stop overbuckling and ski the full day with no pain. So I’m wondering could removing the arch support of the footbed create fit problems for more “normally” arched feet?

    1. The short answer is removing the arch support of footbeds for feet with ‘normal’ arches, which is subjective, (I prefer functional feet and lower limbs) doesn’t create fit problems, it changes the requirements of the constraint applied to the dorsum of the foot which may not have been good even with footbeds.

      Flat feet in itself is not necessary pathological. It takes an expert like Kevin Kirby, DPM or Emily, Splichal, DPM to evaluate the feet in the context of the functional requirements of the target activity to properly assess whether the feet and lower limbs are functionally competent.

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