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Vertical forces produce horizontal progression

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Jan 10, 2019.

  1. scotfoot

    scotfoot Well-Known Member


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    Vertical forces produce horizontal progression during gait . Any thoughts ?
     
  2. scotfoot

    scotfoot Well-Known Member

    During gait , pushing down hard with the standing foot causes the swing leg to move in front of the body faster . Important in balance recovery after a trip ?
    How do some footballers "ping" a pass with very little back lift ? Same mechanics .
     
  3. efuller

    efuller MVP

    The location of the vertical forces relative to the center of mass will tend to produce a rotation of the body. Which way it rotates depends on the relative location of the center of pressure and the center of mass. As the body rotates, there may be some reactive frictional horzontal forces. These horizontal forces cause horizontal accelerations. F = ma.
     
  4. scotfoot

    scotfoot Well-Known Member

    Hi Eric
    We had a discussion about this subject here-
    Vertical ground reaction forces and sprinting


    However , since then, Luke Kelly (1) has produced another good paper on the energy storage properties of the intrinsic foot muscles . I wonder if the stored energy in the intrinsics might be returned to the the system during mid stance as the foot becomes less flattened contributing to vertical acceleration of the pelvis and hence angular acceleration of the swing foot /leg .

    (1)
    Intrinsic foot muscles contribute to elastic energy storage and return in ...


    https://www.ncbi.nlm.nih.gov/pubmed/30462568
    by LA Kelly - ‎201821 Nov 2018 - We recorded foot motion and forces, alongside muscle activation and ultrasound images from flexor digitorum brevis (FDB), an intrinsic foot muscle that spans the arch.
     
  5. efuller

    efuller MVP

    To understand energy, you need to understand joint power. Power is the change in energy. Chemical energy used in muscle contraction creates mechanical energy in the form of motion. Power is equal to joint moment x joint angular velocity. For a muscle to contribute to forward progression it would have to be creating a moment and the joint contributing to motion would have to be moving in the direction of the motion. For the toe muscles, intrinsic and extrinsic, you would have to see plantar flexion of the toe joints and have the inverse dynamics showing a plantar flexion moment.

    In gait, after heel off, the toes are mostly dorsiflexing, so they would be absorbing energy. If they start to plantarflex as the metatarsals leave the ground, they could be contributing some energy to gait. With horizontal friction this force could be both vertical and horizontal.

    Eric
     
  6. scotfoot

    scotfoot Well-Known Member

    Eric ,
    As you are aware , the bony arch of the foot compresses and recoils during gait and this compression and recoil results in , among many other things , a lowering and raising of the tibiotalar joint .

    What I am suggesting is that as the arch recoils , the raising of the tibiotalar joint will help produce angular acceleration in the swing leg .

    Understanding how vertical accelerations can produce angular acceleration can probably best be achieved by looking at a small weighted object tied to a string .

    Hold the string in your hand and gently start the object swinging to and fro . Now a bit of co-ordination is required , but basically as the object starts to descend , lift your hand and therefore the string , upwards . The weight will accelerate . If you repeatedly lift and drop your hand and therefore the anchor point of the string , in a well timed manner , you will continue to impart energy into your pendulum .

    Here is a link to a short video showing the lowering and raising of the tibiotalar joint .
    Over Pronation & Supination Motion Biomechanics of the Subtalar ...


    upload_2019-1-12_11-6-32.jpeg ▶ 1:43
    14 Jun 2012 - Uploaded by DrGlassDPMValmassey's Textbook Clinical Biomechanics of the Lower Extremities is a great reference. I suggest it http ...
     
    Last edited: Jan 12, 2019
  7. scotfoot

    scotfoot Well-Known Member

    So with regard to the above can "spring loaded" shoes/boots improve gait efficiency especially in cases were a load is being carried ie a rucksack or Bergen ?
    I would think it probably can .
    It's not so much about "bouncing along " but more about assisted contralateral swing .
    Interesting .
     
    Last edited: Jan 14, 2019
  8. David Smith

    David Smith Well-Known Member

    Impossible, it is not possible for a force to do work on a mass in a direction at 90dgs to the line of action of the force
     
  9. scotfoot

    scotfoot Well-Known Member

    Do you disagreeing with this from thread 6 ? - "Understanding how vertical accelerations can produce angular acceleration can probably best be achieved by looking at a small weighted object tied to a string .

    Hold the string in your hand and gently start the object swinging to and fro . Now a bit of co-ordination is required , but basically as the object starts to descend , lift your hand and therefore the string , upwards . The weight will accelerate . If you repeatedly lift and drop your hand and therefore the anchor point of the string , in a well timed manner , you will continue to impart energy into your pendulum "



    If your swing leg is on the way down ( and past 90 degrees relative to the standing leg ) and you push up on the standing leg you will create tension in the ligaments etc of the swing leg and it will accelerate . That is a matter of fact .
     
  10. efuller

    efuller MVP

    In your analogy, there are horizontal forces. There is tension in the string that is at an angle to the ground and the tension can be divided into horizontal and vertical components. A better analogy would be taking a pencil and holding it an angle off of vertical, with one end on a surface, and then letting go of it. A the instant you let go, the center of pressure is not directly under the center of mass, so a force couple is created that will cause the pencil to rotate. If the pencil is on a frictionless surface, the center of mass of the pencil will fall straight down. If you have the eraser end of the pencil on the table, the pencil will try and rotate, and the bottom end of the pencil will meet with horizontal friction that will cause the center of mass to accelerate in the direction that the pencil was leaning.

    No. How do those internal forces in the leg create an external force on the entire body?
     
  11. scotfoot

    scotfoot Well-Known Member

    Eric ,
    As we walk our pelvises move up and down in the vertical plane (among others ) .

    So take a pencil to represent the pelvis , and our string with a weight on it to represent the swing leg . Tie the string to one end of the pencil and hold the other end of the pencil in your hand .

    So now you have a pencil held out from your hand parallel to the ground and from this dangles the string . Now lift your hand vertically up and down to represent a straightening , lifting stance leg . The string and weight will simply mimic this up and down movement .

    However , if you first start the weight and string moving to and fro , as in a pendulum , then when you lift and drop the held end of the pencil , energy will be imparted into the swinging weight . If you've got rhythm that is !

    And so yes , " Vertical forces produce horizontal progression during gait . " Not "impossible" since accelerating the swing leg will cause it to advance , in part , horizontally .
     
  12. David Smith

    David Smith Well-Known Member

    Scott, Assuming you're replying to me with this answer!? The principle that a force cannot act perpendicular to its line of action is immutable, the force that cause a change in direction of the object on the string is the centrifugal force of the string. What you are doing by moving your hand up and down is adding energy to the system as you correctly point out..
     
  13. scotfoot

    scotfoot Well-Known Member

    David
    Are you accepting that in broad terms "Vertical forces produce horizontal progression during gait " in the way outlined in post #11 above ?
     
  14. David Smith

    David Smith Well-Known Member

    In very broad terms, in the same way that you could say that the vertical force acting on a piston drives the car forward - but in fact its the horizontal force of the tyres acting against the road that drives the car forward. Do a free body diagram and see if the body can move forward, just with vertical forces and without any horizontal force
     
  15. scotfoot

    scotfoot Well-Known Member

    We seem to be in agreement . The stance leg drives the pelvis up etc .
     
  16. Still don’t understand why a dentist is so fascinated by human gait. Depends whether you are talking about walking or running gait and when within the gait cycle we are considering. If you are talking about the propulsive phase of the stance limb during walking gait then it should be recognised that during this period the centre of mass is falling. This does not fit with the notion of the stance limb driving the pelvis up. Perhaps you should enroll at podiatry school, Gerald.
     
  17. scotfoot

    scotfoot Well-Known Member

    Who's Gerald ?
     
  18. What is your real name? Oh that’s right it’s Gerard not Gerald because this is you isn’t it? http://news.bbc.co.uk/1/hi/scotland/3714954.stm. I was close it's tricky when people don’t use their real names.
     
  19. scotfoot

    scotfoot Well-Known Member

    What on earth are you talking about ?
     
  20. David Smith

    David Smith Well-Known Member

    yes, in that - The stance leg drives the pelvis up (sometimes) but not etc
     
  21. Your real name.
     
  22. scotfoot

    scotfoot Well-Known Member

    Simon ,what exercises do you recommend to your patients for intrinsic foot muscles strengthening purposes .
     
  23. scotfoot

    scotfoot Well-Known Member

    An so meanwhile , back on the topic at hand and and away from Simon and the missing "r" in the reporters story (Gerard rather than Gerrard ), which led him to use the name Gerald ?
    During walking it is my understanding that the pelvis is at it lowest point in double support and so this fits well with the general idea of vertical displacement of the pelvis causing acceleration in the swing leg as walking progresses .

    True that supination may not contribute in the walking scenario but that's ok because it all just theory up for discussion .
     
  24. Couldn’t remember your name because you hide your identity behind a pseudonym here. Remembered that you were a dentist that got chinned by a patient, so I googled you to get your name. Why is a dentist so interested in all of this? Moreover, what was wrong with his dentures and why did he feel you had made them too big? When you are making dentures what kind of casting technique do you use with your patients? Have you noticed that most of the time you are the only person replying to your own posts on Podiatry Arena, Gerrard (with two r's)? Have you considered why this might be?
     
    Last edited: Jan 17, 2019 at 3:53 PM
  25. Orthican

    Orthican Active Member

    Simon, Why is it such a bad thing that someone wants to learn? :ie scotfoot? My understanding from before was that you are an educator? Surely that would mean you are open to teaching. I do not post here anymore or bother with it much as this is the kind of thing that shows up here a lot. If ego and elitism were the standards for entry to podiatry arena then it seems that would make more sense. I came here some time ago to get more information about biomechanics of the foot as I wanted to understand better for my patients. It is about them after all that I do this work. When I give lectures to those wanting to learn about upper extremity splinting for stroke etc. my discussion to those wanting to learn and ask questions revolves around mutual respect because we all want to learn. Few people these days want to it seems . Some are content to sit on what they have learned in the past and consider it done. Others like to learn about more. That should not be shunned it should be encouraged. Sorry for talking. I know I'm not a podiatrist so my opinion here matters little so if you could please forgive me.
     
  26. This site was set up as a forum for academic discussion between podiatrists and those professionals involved in foot health- the last time I looked dentists were not professionals involved in foot health. From the outset it was made clear that this was not a site for patients to come and ask questions about the problems they were having; later it was made clear that this was not a forum for barefoot running zealots to air their views etc. Over the years, (and many of us have been here from the outset and were actually actively contributing to the predecessor of Podiatry Arena over 20 years ago) there have been a vast number of people who have come here in the hope to use this site as an advertising vehicle to sell a particular product. This occurred to a level in which it became intolerable to the vast majority of regular posters, hence many of us have stopped posting at all. So when a dentist comes on here and repeatedly asks questions regarding the plantar intrinsic muscles of the foot, the skeptical mind asks- "why is a dentist repeatedly posting questions about the plantar intrinsic muscles of the foot?" and "what's this guy selling?" When he has been asked these question directly, you don't get an answer (see above). So over time people like myself and Kevin Kirby who the records will show, were the main contributers to this site for many years, withdrew from interacting with Gerrard because despite him asking lots of questions, he rarely if ever gave a response to our questions of why a dentist was so interested in all of this? He then started going on about how someone had nicked his ideas from here and should have referenced his comments from here in their paper (which incidentally had probably been submitted for and accepted for publication long before Gerrard had written anything). All of which makes someone like me suspicious of someone like Gerrard. Which is why I seldom choose to interact with him nor indeed spend my time in education with people reading Podiatry Arena anymore. I'm guessing I'm still allowed to choose who I want to interact with, and moreover, to educate and that I am entitled to say what I think still despite living amongst the offended, snow-flake generation?
     
  27. Orthican

    Orthican Active Member

    Thanks for replying. Then with all you have said perhaps this site should be ADVERTIZED as podiatrist \ foot professional ONLY and stated very clearly at the opening front page that NO OTHER interactions are or will be tolerated. Then those of us professionals outside of your loop will know to just stay away. However, as it is an open forum and seems to be set up on the internet as such then those of us unsuspecting fools and advertizers who see it come up in a search for foot related issues and see it as a place to ask questions will probably do so. To their regret it seems. Get Craig to close the loop then. I mean you well Simon. I don't know you but I do respect you.
     
  28. There used to be a statement on the homepage, which people ignored. To be honest no-one really uses this site anymore anyway. Edit: it's still there- https://podiatryarena.com/index.php?threads/forum-rules.628/ Thanks for the patronisation though.
     
    Last edited: Jan 17, 2019 at 6:57 PM
  29. scotfoot

    scotfoot Well-Known Member

    This is not your site Simon and you don't make the rules , Craig does .
     
  30. Good luck with your future Gerrard.
     
  31. scotfoot

    scotfoot Well-Known Member

    You said "Couldn’t remember your name because you hide your identity behind a pseudonym here "

    And yet my name , Gerrard Farrell and city , Glasgow appear on every one of my posts .

    That's 444 times .

    You said "To be honest no-one really uses this site anymore anyway " . And yet membership continues to grow .
    Why not just block my content ?
     
  32. Simon:

    I couldn't agree more. Like the UK-based JISC Podiatry Mailbase before it, I believe Podiatry Arena may have run its course as being a place where I want to actively contribute. It was great fun over the years having debates with yourself, Howard Dananberg, Bruce Williams, Eric Fuller, Craig Payne, Daryl Phillips and many others on these internet-based podiatry discussion forums.

    Maybe it's time for a new internet venue where we can share ideas and debate like the old times. Now, unfortunately, when a dentist and "NewsBot" are posting up the only comments on PA, something is very wrong.
     
  33. Except it doesn’t when you are viewing the site through a mobile device like the i-phone I was using yesterday to read your pish, see image attached.

    Like Kevin said, a dentist and newsbot is all that's left

    Goodbye Gerald, turn off the light on your way out. Screen Shot PA.jpg
     
  34. scotfoot

    scotfoot Well-Known Member

    Simon ,
    You need podiatry arena more than it needs you . Without it you will simply fade away.

    Kevin,
    I have been on to your twitter page and to be honest it's just regurgitation . Podiatry arena continues to grow

    Back to you Simon .Could you tell me what exercise you recommend to your patients for strengthening of the intrinsic foot muscles ?
     
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