Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

Rearfoot force / Forefoot force cross over point analysis

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Phil Rees, Oct 1, 2011.

  1. Phil Rees

    Phil Rees Active Member


    Members do not see these Ads. Sign Up.
    The Tekscan in shoe measurement system allows the user to establish discreet areas of investigation. The frames option allows for the foot to be divided into rear foot and fore foot sections that can then be displayed in the various graphical options. The force option graphical display shows the rise and decline of the rear foot force and the rise and decline of the fore foot force. There's a point on the graph where the graphs "cross over" each other and form a "cross over pyramid".
    I've been extracting the raw ASCII data and plotting the incline of the fore foot force and the decline of the rear foot force up to the point where the y axis values are the same and form the apex of the "cross over pyramid". The software I'm using allows me to quantify the area under the cross over pyramid by using the Simpson equation so I can assign a crossover impulse value to the graph.
    The questions I'd like to ask are ...
    1. Is being able to quantify the value of the "cross over pyramid" of any clinical value
    2. Is the magnitude of the cross over point on the Y axis significant
    3. Is the time point of cross over on the X axis significant
    4. and ... what is the shape of the cross over pyramid telling us about the foot is functioning
    Any comments would be very much appreciated
    Phil
     
  2. Craig Payne

    Craig Payne Moderator

    Articles:
    8
    The assumption/rationale behind this is that the further posteriorly the 'cross over' point (ie the sooner load gets off the heel and gets to the forefoot), then the assumption is that this is a good thin and a sign of an efficient forward movement of the loads. If there is a delay in this forward "flow", then the 'cross over' point will be more anterior and the assumption could be that this is a sign of an inefficient gait.

    As it if this is a good measure, there are several others that would give similar findings:
    - the timing of load leaving the heel
    - the timing of the load getting to the forefoot
    - the slope of the force curve as load comes of the heel
    - etc

    They all sort of measuring the same thing.

    In PTTD, the clinical usefulness of this is more obvious; there is usually a massive delay in these parameters in PTTD (ie delayed heel off) ..... so if you get the foot orthotic/shoe combination in these people right, then there should be a return of these parameters closer to normal/ideal values - if not, then something needs to be done to get them there (?can we assume that the orthotics do not work if they do not restore those parameters closer to normal???)

    In plantar fasciitis, you see a similar thing, but the delay in those parameter is much more subtle.

    This is a significant angle for further research ... ie relationship of those parameters to pathology and the relationship of those parameters being altered to predict (or not) clinical outcomes with foot orthotics.

    A lot of people are talking about these parameters (or their variation of them) and using them clinically ... its just the data that is lacking from research that is missing.
     
  3. efuller

    efuller MVP

    Hi Phil. A few years back I had access to an EMED force platform and it was easy to divide the foot in half with that as well. I did a lot of thinking about the curves that you describe.

    The crossover itself may not have any clinical value, but there are things that are related to it that may have some value.

    The magnitude of the cross over point will be related to the total force at the cross over point. The total curve, in walking, usually shows two force peaks. The cross over point usually occurs in the trough between the two force peaks. Some people say there is some importance to the shape of the curve between the two force peaks, I'm not so sure that there is. It will be related to the upward acceleration of the body. So, I would look for a clinical significance in upward acceleration of the body and not necessarily at the cross over point.

    The cross over point is where the weight on the back portion (arbitrarily assigned) of the foot is equal to the front portion of the foot. People with an early heel off will have an earlier cross over point. The question then becomes how early of a heel off is significant?

    The shape is related to how quicly force is transferred from the rearfoot to the forefoot. For example, if someone had a very week gastroc-soleus and a very large amount of ankle dorsiflexion range of motion available, then they would have weight on the rearfoot for a lot longer period of time and this would alter the crossover curve.

    One theory of orthotic function is that when the foot hurts, or would hurt, if you had a higher amount of ankle joint power, then the person will choose to delay contraction of the gastroc soleus so that weight would stay on the heel longer. Ankle joint power is ankle joint angular velocity x ankle joint moment. The moment can be calculated from inverse dynamics. Power tells you how much a particular joint is contributing to the motion that you see. So, if you have higher moment and higher angular velocity, you will tend to see an earlier heel off. So, there may be a correlation between the "crossover curve" and ankle joint power. However, if I had the equipment, I think that I would rather measure ankle joint power.


    Eric
     
  4. Phil Rees

    Phil Rees Active Member

    Here's two examples of the cross overs .... the first graph is the crossover in isolation. The numerical value is the area under the pyramid
     

    Attached Files:

  5. Surely much of this is determined by where you place your masks? How is the position of the forefoot versus rearfoot masks decided?

    Not sure what the area under the triangle is equal to? What do you think it is equal to, Phil? The area under a force- time curve is impulse or change in momentum, so is this the change in momentum from the rearfoot to forefoot segments? Questionable. Is it the combined momentum for the foot at this time- questionable too. What do you think it is that you are measuring, Phil? It is a proportion of the impulse, but I'm not sure how we'd define exactly what that proportion is. Anyone?
     
  6. Further, what is obvious is the 10mm rocker on the metatarsal heads caused the forefoot to load simultaneously with the rearfoot= skinhead moonstomp boots http://www.youtube.com/watch?v=YlWxvlQ8Zy4 = cool. I'd go with 10mm MTH at the rearfoot with your rocker 10mm @ 55% at the forefoot. I'm guessing you can't do that so failing that, go with your standard or low toe ;-) Low toe. Jedi.
     
Loading...

Share This Page