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"external loading rate" & "mechanical work"

Discussion in 'Biomechanics, Sports and Foot orthoses' started by DamNative, Jun 8, 2010.

  1. DamNative

    DamNative Welcome New Poster

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    Hi everyone,

    I'm an Exercise Science student doing an assessment where we research a topic of choice. I've been researching barefoot vs. shod running and need help with understanding the aforementioned terms in the title.

    They were used in the following context.

    "Barefoot running is characterized by a significantly larger external loading rate than the shod condition."

    "mechanical work is significantly higher in the barefoot condition..."

    I'm very much out of my depth when it comes to the biomechanics of gait, so if anyone could fill me in on what these terms mean it would be much appreciated.

  2. :welcome: to Podiatry Arena.

    Heres my take.

    external loading rate Ground reaction Force (GRF) over a shorter time

    mechanical work the effort required by the muscle in slowing motion ie eccentric contraction and creating movement concentric contraction

    So in barefoot running the GRF will be increased under the forefoot due to FF striking position, but it will occur over a reduced time and the mechancial work on the achilles tendon is significantly increased, more in the eccentric contraction way.

    Hope that helps, I´ve just noticed something new thing if you highlight the terms that you asked about and click on the highlighted section and you will get links which may help.
  3. DamNative

    DamNative Welcome New Poster

    okay, I now understand the "mechanical work" part, but the "external loading rate" part is still going over my head. Are you saying that the barefoot condition has a higher peak vertical force than the shod? Or is that something different altogether?

    thanks for the welcome and fast reply too. Really enjoying the barefoot vs. shoe running debate, interesting read!
  4. I won´t send you up the wrong path as it seems that research is not as clear as it seems.

    Check out this link it may help.


    As I said the above was my take ( which may not be 100% correct) hopefully someone else will answer your questions if the link does not as Ive not spent alot of time playing with force plates etc and don´t want to give you wrong info.
  5. David Smith

    David Smith Well-Known Member


    Rate of load means - applied force with respect to time. The external part means forces applied from outside the body i.e. Gravity and friction as ground reaction forces and not muscle or joint forces.

    The term 'larger external rate of loading' is quite ambiguous since it gives no clues as to what part of the stance phase ground reaction forces are of interest. So the first 50milliseconds of heel strike may have a high rate of loading but what about the rest of the stance phase, what is the nature of that loading?
    I would prefer to use faster or shorter in terms of a loading rate and so a faster loading rate could be characterised on a graph as a steeper slope where y / vertical axis= force and x / horizontal axis = time.

    However, since load over time is usually not a straight line slope graph, the nature of loading is better expressed or characterised as an impulse or integral but that may be taking a step to far for now.

    'Mechanical work' if used as a term of Newtonian mechanics or physics means precisely - force x displacement. So a force of 100 Newton applied and causing a 10 meter displacement is 10 times less work than 100 Newtons applied over 100 meters and the same a 10 Newtons applied over 100 meters. This is expressedin units as Ns (Newton seconds) or Joules.

    NB the displacement must be in the direction of the force. It might be useful to consider that a train travelling at a constant speed or velocity does no on a passenger work even though it may transport you 100miles. This is true (for the sake of this argument) since force requires acceleration (f=mass*acc)and if there is a constant velocity there can be no force applied so therefore no work can be done.

    The rate of work is 'Power' and power is => work divided by time.

    Work done by muscles as Physiological work is measured in terms of energy (joules) like the energy of a burning fire might, i.e. its has energy but no displacement, and is not necessarily mechanical work since mechanical work is defined by displacement and if there is no displacement then no work is done. (Disregarding the concept of negative work here)

    So, how these terms apply to your problem is quite vague unless in context and precisely defined.

    A high rate of load over a short time does not equal much work done.
    A large displacement with a small force is a small amount of work done (relatively speaking)
    Perhaps significantly higher mechanical work refers to the fact that there is more displacement done by the external forces.

    The most likely explanation is that they found the shoes attenuated the applied external forces more than the barefoot. NB Attenuation of a force spreads the application of force over time so that the peak force is reduced but the time element is increased. So the force time curve is longer and flatter or can be said to have a lower frequency.

    Mike wrote
    Which may be reasonable in terms of a simple explanation and what the writer may have meant but makes lots of unsupported assumptions. E.G. The peak or mean forces may be increased under the forefoot of the barefoot runner in relative terms but the rate of loading in the shod foot may be higher if the subject chooses to then adopt a heel strike style, as can be the case but is unknown here.

    If this were the case then one might expect attenuated forces using forefoot strike compared to heel strike and so the load rate would be reduced in the barefoot not increased.

    The fact that there is increased load rate in the barefoot runner makes me assume heel strike in both cases and GRF attenuation is caused by the nature of deformation of the shoe heel material as compared to the anatomical heel tissues.

    Perhaps you could attach the paper you are referring to so we can get better insight into your problem' also you could read the threads on barefoot v's shod running http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=43282
    or http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=43282 for example.

    Cheers Dave Smith
  6. David Smith

    David Smith Well-Known Member


    I just noticed a deliberate mistake
    should say Nm or Newton metres or joules

  7. Native:

    External loading rate is measured on a force plate and will be the slope on the ground reaction force vs time curve when the individual walks or runs over the force plate. The steeper the slope, the higher the external loading rate.

    Mechanical work refers to internal muscle/tendon/ligament work where the body is resisting the effects of ground reaction force. Work is force or moment multiplied by distance or angular rotation of a joint.

    Hope this helps.
  8. DamNative

    DamNative Welcome New Poster

    Thank-you to all for the in-depth responses.

    These are the papers which mention the "external loading rate" and "mechanical work" respectively.

    Biomechanical analysis of the stance phase during barefoot and shod running - De Wit et al.

    Barefoot-Shod Running Differences: Shoe or Mass Effect? - Divert et al.
  9. http://www.rsscan.de/images/download/1_05.pdf
  10. Griff

    Griff Moderator

    Here's the other one


    Attached Files:

  11. Griff

    Griff Moderator

    Here's another by the same authors

    Attached Files:


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