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Is the pressure time integral of an average step a valid quantification value?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Phil Rees, Jan 9, 2013.

  1. Phil Rees

    Phil Rees Active Member

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    As part of our therapeutic footwear design process, we now regularly use in shoe pressure measurement (Tekscan) as a way of comparing the design characteristics of new designs of modular footwear soles before we commit to the cost of moulds and tooling. The Tekscan system allows us to obtain an average of the values of several steps into one single "representative" force time and pressure time curves from which we can compare the various graph features and values. Integrals are now commonly used as a way of taking into account not only the magnitude of the pressure/force but also the duration of the load by quantifying the area under the pressure/force time curve. Unfortunately the Tekscan system does not give an integral of an averaged pressure time curve By using the free to download Padowan software we can extract the averaged data as an ASCII file and draw mathematical graphs in an X Y coordinate system. The software has an integral function that assigns a numerical value to the area under the graph. So, we can now quantify the pressure and force integrals of a complete average step or discreet areas of the average step and compare the values between different sole designs.
    My question is therefore, If we wish to investigate the pressure or force characterises of a new sole unit design, is using an integral of the average of several steps a valid way to compare or should we be looking for other ways to quantify their pressure/force characteristics?
    Your comments would be appreciated.
  2. Craig Payne

    Craig Payne Moderator

  3. Phil, in addition to Craig's post above that suggest that the pressure/ time integral doesn't bring any value added to the party, I guess the questions you need to answer are these:
    1) is the pressure/ time integral predictive of pathology in isolation?
    2) is the average pressure/ time integral predictive of pathology in isolation or could the average integral be influenced by single excessively high or low integrals and mask a potential problem? (are you disregarding out-liers within the data set?, will a single step's integral result in pathology?)
    3) does the f-scan system provide valid and repeatable measure of the pressure/ time integral?
  4. Phil Rees

    Phil Rees Active Member

    Thank you Craig
  5. Phil Rees

    Phil Rees Active Member

    Simon, apologies for my delay in responding.
    Three very good points. We tend not to disregard individual steps unless we observe something very different within the graph, then it's a completely subjective decision as to it's exclusion. We conduct all our studies on a treadmill because of space limitations but again this raises important questions as to how valid are the resultsfrom.
    As for the validity of Tekscan ... well it's the best we've got and could afford at the moment
  6. Using both peak force and pressure-time integrals should be useful measurements for predicting potential injury to plantar tissues. With in-shoe plantar measurement systems, one of the beauties of their design is that you can isolate a specific area of the foot of interest (e.g. 2nd metatarsal head) and then use ten different shoe designs to see how each shoe affects the loading characteristics of that anatomical structure.

    Of course, these systems also have the disadvantage of 1) not being able to measure any of the anterior-posterior or medial-lateral shearing forces present at the foot-shoe interface which are also known to cause plantar soft tissue injury, and 2) being less accurate at measuring true forces as the measuring sensels are more non-horizontal. You may want to read this reference to better understand the benefits and limitations of such systems.

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