The Minimalist Index for running shoes

One of the problems with running shoe research is that different running shoe manufacturers use a different set of design features to try and achieve the same effect. For example, there are a number of different design features that could be considered attempts at ‘motion control’. If a study uses a shoe with one of these design features and finds it does not work (or does work), should the results be extrapolated to all motion control shoes (which is what usually happens) or just to shoes with that particular motion control design feature? With minimalist running shoes there was a clear lack of a consensus definition and there are a number of different design features that go into what some would consider a minimalist running shoe. Two different minimalist running shoes with a different set of what is considered minimalist design features may give different results in a study. Even some of the maximal running shoes could have what some might consider a minimalist design feature (eg zero drop). This study set out to address some of these issues:

A consensus definition and rating scale for minimalist shoes
Jean-Francois Esculier, Blaise Dubois, Clermont E. Dionne, Jean Leblond and Jean-Sébastien Roy
Journal of Foot and Ankle Research 2015, 8:42 doi:10.1186/s13047-015-0094-5
Background
While minimalist running shoes may have an influence on running biomechanics and on the incidence of overuse injuries, the term “minimalist” is currently used without standardisation. The objectives of this study were to reach a consensus on a standard definition of minimalist running shoes, and to develop and validate a rating scale that could be used to determine the degree of minimalism of running shoes, the Minimalist Index (MI).
Methods
For this modified Delphi study, 42 experts from 11 countries completed four electronic questionnaires on an optimal definition of minimalist shoes and on elements to include within the MI. Once MI was developed following consensus, 85 participants subjectively ranked randomly assigned footwear models from the most to the least minimalist and rated their degree of minimalism using visual analog scales (VAS), before evaluating the same footwear models using MI. A subsample of thirty participants reassessed the same shoes on another occasion. Construct validity and inter- and intra-rater reliability (intraclass correlation coefficients [ICC]; Gwet’s AC1) of MI were evaluated.
Results
The following definition of minimalist shoes was agreed upon by 95 % of participants: “Footwear providing minimal interference with the natural movement of the foot due to its high flexibility, low heel to toe drop, weight and stack height, and the absence of motion control and stability devices”. Characteristics to be included in MI were weight, flexibility, heel to toe drop, stack height and motion control/stability devices, each subscale carrying equal weighing (20 %) on final score. Total MI score was highly correlated with VAS (r = 0.91). A significant rank effect (p < 0.001) confirmed the MI’s discriminative validity. Excellent intra- and inter-rater reliability was found for total MI score (ICC = 0.84-0.99) and for weight, stack height, heel to toe drop and flexibility subscales (AC1 = 0.82-0.99), while good inter-rater reliability was found for technologies (AC1 = 0.73).
Conclusion
This standardised definition of minimalist shoes developed by an international panel of experts will improve future research on minimalist shoes and clinical recommendations. MI’s adequate validity and reliability will allow distinguishing running shoes based on their degree of minimalism, and may help to decrease injuries related to footwear transition.

I was part of the delphi group exercise so have known of this study for some time and have been pestering the authors as to when it was going to get published, so good to see it in print. The full text can be read at JFAR. This was a two part study in which the first part went though several iterations to arrive at the different design features in running shoes via a delphi process to arrive at the consensus definition of a minimalist running shoe:

Footwear providing minimal interference with the natural movement of the foot due to its high flexibility, low heel to toe drop, weight and stack height, and the absence of motion control and stability devices”

The second part of the study was the testing of a minimal rating scale (the PDF of the rating scale is here). The use of this rating scale means that if one particular shoe is used in a study, the design features or characteristics of that shoe can be compared to the results of another study that may or may not have got the same results. Any differences between the study could be explored with the use to this rating scale and the combination of design features that the shoes used in the studies had. This goes some way to dealing with the issues I mentioned in the opening paragraph above.

The only problem I have with this concept is pedantic and semantic, in that why “minimalist index”? Why not just “running shoe index”? I know the goal of the authors was to identify the degree of minimalism in a running shoe, but the index also identifies the degree of maximalism in a running shoe as well. Not sure I get the rationale behind the naming of it, especially in the context of the recent emergence of the maximal running shoes and the decline in interest in minimalism. The sales of minimalist running shoes have continued to decline since around mid-2013.

As always: I go where the evidence takes me until convinced otherwise, and having a rating scale and accurate descriptions of the different design features in any study of running shoes is important to compare results across studies. This index does that.

Esculier, J., Dubois, B., Dionne, C., Leblond, J., & Roy, J. (2015). A consensus definition and rating scale for minimalist shoes Journal of Foot and Ankle Research, 8 (1) DOI: 10.1186/s13047-015-0094-5

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7 Responses to The Minimalist Index for running shoes

  1. blaise August 31, 2015 at 11:32 pm #

    CP : Why “minimalist index”? Why not just “running shoe index”?

    BD : You are absolutely right!!

    blaise

    • Roman R. September 2, 2015 at 6:01 am #

      Maybe because the incarnation of maximalist shoes like the Hoka would’t score 100% due to their weight? I guess there are also neutral maximal shoes without pronation control that I would stil describe as entirely maximal.
      The main feature of maximal shoes is the cushioning so if applying the same items of the MI they should at least be weighed differently and not equal.

      • Craig Payne September 2, 2015 at 6:12 am #

        The Hoka’s wouldn’t be “100%”; they would probably be a 0 in weight; a 0 in stack; a 4 in drop; 3 or 4 in motion devices; 2 or 3 in flexibility, so Hoka score would probably be around 10; most minimal score is 25 and most maximal score is 0.

        • Roman R. September 2, 2015 at 6:20 pm #

          That given, do you think the Hoka’s are adequately distinguishable with the MI score from other not maximal running shoes?
          Wouldn’t a supportive shoe with lower stack but higher drop achieve similar scores?
          I could also imagine a trail running shoe like the Speed Cross 3 would score even lower than a Hoka but it’s clearly not what I would define as a maximal shoe.

          • Craig Payne September 2, 2015 at 9:54 pm #

            I haven’y yet tried to classify many shoes on the Index, but the Hoka does well on the “minimalist” feature of ‘low drop’ and not a lot of the ‘motion control’ design features ….

  2. Roman R. September 3, 2015 at 9:36 am #

    I’m not convinced that the score works both ways.
    While the max. values actually represent the features of the most minimal shoe quite well, do the min. values not necessarily depict the features of a maximal running shoe. Probably there doesn’t even exist a running shoe with a 0 score, ’cause nobody would run in that kind of shoe.
    The design features of a maximal shoe aren’t that straight forward like those of minimal shoes. Thats why there are, as I tried to illustrate in my previous post, shoes with similar scores although beeing very different.
    You can probably find maximal, supportive and trail running shoes with the same score and the only conclusion you can draw is that they are not very minimal but not the degree of maximalism.

  3. Rodger Kram September 9, 2015 at 3:58 am #

    Nike uses the opposite scale. i.e. a larger # = more shoe.
    Free 5.0 is more shoe than Free 3.0
    Nike “defines” 0.0 = true barefoot running.

    I think that sort of directional scaling makes more sense.
    If in the future, there are shoes with 40mm drop that have a mass of 500grams, that could still be accommodated.
    Or, if a 50 gram shoe is created, it would not need a negative mass score.

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