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Average Newton Meters of Force from a walking and running footstep

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Bruce Williams, Feb 7, 2019.

  1. Bruce Williams

    Bruce Williams Well-Known Member


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    Hi everyone,
    I have a question regarding the average numerical force of a footstep from running and walking.
    This is reference to deforming forces on orthotic materials. A manufacturer suggested that 110nm of force was a good average for testing deformation of orthotic materials. I'm not sure if that is correct or not, so I am asking for myself and for the manufacturer.
    Any help or direction to the answer appreciated.
    Cheers,
    Bruce Williams, DPM
     
  2. efuller

    efuller MVP

    Are you concerned about breakage/failure, or are you concerned about resistance to deformation? The shape of the orthotic will dramatically affect the bending stiffness of the orthotic with the same material.

    Newton meters is a unit of torque for rotational motion or a unit of work for linear motion. Newton is a unit of force. For testing bending strength there should be a distance in the equation because the testing usually occurs with two ends supported and the distance between the supports will affect the bending moment. A bigger foot will have larger distance to the supports.

    The absolute number doesn't do you much good. What you want is a comparison with something that you know e.g. 5/32" polypropylene.
     
  3. A
    Also depends on the area you going to load it over. When I did my FEA analysis I used 500N, 1000N and 1500N loading vertically downward evenly across the surface. I also used some data from F-scan where I took pressure readings and sensel size. I could try and find that if it would help, Bruce.
     
  4. Newton (N) is a measure of force. Newton-meter (Nm) is a measure of moment (i.e. torque). If you are applying force to an orthosis, it would be measured in N, not Nm. If a 180 pound (800 N) individual stands on one foot, probably a force of at least 400 N is applied to the rearfoot and midfoot portions of the orthosis plate in standing. During running the forces would be much higher. If I were doing the test, I would want to apply at least 200 N to the medial arch of the orthosis with a plunger over the apex of the medial longitudinal arch repetitively for at least 100,000 cycles with a material testing machine to test for orthosis deformation over time.
     
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  5. Petcu Daniel

    Petcu Daniel Active Member

    I think Ian could be of help as he presented some data at COP Conference in 2017 : https://jfootankleres.biomedcentral.com/articles/10.1186/s13047-018-0246-5

    P01 Is the medial longitudinal arch stiffness of a foot orthosis influenced by commonly used prescription designs?
    Ian Griffiths1, Zakiyyah Bibi Auchoybur2, Martin McGeough3, Julia Shelton2

    Background: Foot orthoses have historically been issued in the belief they may positively improve (or correct) skeletal alignment. Despite practitioners worldwide subscribing to this kinematic mechanism to explain how foot orthoses work, the published literature is rather inconsistent in its support for this. However, data does support the contention that foot orthoses may exert their effects via a kinetic mechanism (i.e. the modification of the location, magnitude, vector or temporal patterns of reaction forces at the foot-orthosis interface). As such great interest should be taken in how the design of a foot orthosis may influence its ability to generate reaction forces. One feature of orthosis design which is likely to be key here is the load-deformation characteristics (stiffness) of the shell.
    Methods: The choice of material prescribed, its thickness and also its geometry will all affect shell stiffness and the subsequent influence of kinetic parameter changes. In this study we took prefabricated orthoses with semi-rigid polypropylene shells, 3mm in thickness, EUR size 42 (KLM Labs, USA) and compared the load-deformation characteristics in the medial longitudinal arch across three different conditions which represented commonly used prescriptions in clinical practice: [1] unmodified shell [2] shell with addition of 6mm heel raise [3] shell with addition of 4 degree varus extrinsic rearfoot post.
    Results: The devices were fixed to a flat compression plate and vertically loaded from above with an indenter at the highest point of their medial arch at a rate of 10mm/minute using an INSTRON-5691 (UK) mechanical test machine. The results suggest that the addition of a 6mm heel raise and a 4 degree varus extrinsic rearfoot varus post increased the media longitudinal arch stiffness of the devices by 25% and 35% respectively.
    Conclusions: Whilst this methodology did not perfectly simulate in-vivo loading (and care must also be taken at this time to extrapolate the findings to devices of different materials, thickness and geometries) it may provide some interesting insight into how commonly used prescriptions are altering the ability of an orthosis to introduce kinetic changes. Considering one possible clinical application of this information, it may be reasonable to conclude that if a patient/athlete complains that their devices are too ‘hard’ a first line option could be to remove any extrinsic posting at the rearfoot – this should decrease the stiffness (increase the compliance) of the device and improve tolerance and comfort.
     
  6. Average weight of adult male in the USA is just shy of 90kg so about 880 N when standing on one foot going through each foot, obviously not all of the foot on the shell if 3/4 length device so I’d say your 100ish Newtons is on the low side. Personally, I’d measure stiffness- taking multiple measures of load/ deformation at the points of interest.
     
  7. I imagine that my 200 N would be a good starting point for each load cycle at the apex of the medial longitudinal arch of the orthosis. However, considering 5,000 steps per day as a starting point, 365 days per years, and the expectations that the orthosis should last at least 3-5 years, then probably 5,000,000 - 10,000,000 cycles at 200 N on the materials testing machine would be a better test of orthosis durability than my original 100,000 cycle estimate.
     
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