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Joint moments in forefoot vs rearfoot strike running

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Feb 20, 2012.

  1. efuller

    efuller MVP

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    I don't understand your first sentence. When you describe forces you need to name the object that applies the force and the object that the force is applied to.

    Forces are not always equal and opposite. Look at newton's second law. Net force = mass x acceleration. To have a net force all forces are not going to be equal and opposite. We can use this to solve our question by working in the opposite direction that we have been. A person is standing. Their body accelerates upward. From Newton's second law we know that there must have been an upward net force. Let's say this net force acting on the body is from the ground. Even though there is an acceleration, there is still an equal and opposite force acting at the foot ground interface. To name these forces: there is force from the foot applied to the ground that is equal and opposite to the force from the ground acting on the foot. Only one of those equal and opposite forces are applied to the body. The other is not. However, if we look at the forces applied to the body, the force from the ground acting on the body is greater than than the force of gravity acting on the body. This is why the body accelerates upward.

    The ankle planar flexors can move the body in isolation. However, if you want to remain standing, without any other external forces, or taking a step, you have to lean forward so that your center of mass is over your forefoot. Even, if you don't put your center of mass over your forefoot, you will still move upwards, but you will tend to also move backwards.

    Another example, lie on a nice smooth hardwood floor while wearing a fleece jacket. Lie so that your feet are against the wall. Plantar flex your ankle and you will move without activating any other muscle besides the triceps surae.

    Eric
     
  2. timharmey

    timharmey Active Member

    Simon
    I think you may be right.I can only do it moving forward and can feel my back tense if I lean back and put my weight over my heel no lift off
    Tim
     
  3. David Smith

    David Smith Well-Known Member

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries


    I will,

    "In a mechanical system, any mechanical system, whether static or in motion, there is always equilibrium of forces and moments" Quote (or close enough as remembered) Prof S Nicol Strathclyde Uni Dept of Bioengineering.

    Proof:

    Static equilibrium

    => (force (a) * lever arm (a)) - (force (b) * lever arm (b)) = zero

    Dynamic equilibrium (with no acceleration i.e. constant linear velocity or angular velocity)NB no acceleration = no force.

    => (force (a) * lever arm (a)) - (force (b) * lever arm (b)) = zero

    Dynamic equlibrium (with acceleration linear or angular) we are considering angular displacements so:

    => [(force {a} * lever arm {a}) +( inertal force {a1}) * lever arm (a1))] - [(force (b) * lever arm (b) + (inertial force (b1) * lever arm {b1})] = zero

    so now we know that; force * lever arm = moment (M)
    and Inertial force * Lever arm = inertial moment (I)

    so - Re write like (Ma + Ia) - (Mb + Ib) = 0

    Now obviously acceleration can only be in one direction at a given time and inertial force is in the opposite direction to the acceleration. Therefore if Ma is clockwise then moment due to Ia is anticlockwise and moment Ib is zero. So if we give clockwise a minus sign and anticlockwise positive then:

    (You might note here that Inertial force can be/has been called fictitious since it does not have a direct equal and opposite force e.g. Ib is always zero relative to Ia.)

    So now; (-Ma+Ia)+(Mb) = 0

    So now rearrange the equation to -Ma+Mb = Ia which is the more familiar scenario of one moment being larger than the opposing moment (external V's Internal) that will result in acceleration of the limb of interest.

    So remembering F=MA then to find the acceleration of the limb of interest A=F/M

    Regards Dave
     
  4. Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Eric:

    Can't agree with you on that one. Newton's Third Law of Motion states: For every action, there is an equal and opposite reaction.

    http://www.physicsclassroom.com/class/newtlaws/u2l4a.cfm
     
  5. David Smith

    David Smith Well-Known Member

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    From the equations in my last post you can see that there is a force that is not equal and opposite since it is the result of and reaction too acceleration ( as Eric said earlier)
    So as in Eric's example when the man jumps then there is an inertial force plus gravity*mass acting opposite to the ground reaction force produced by muscular effort therefore the sum of forces is equal.

    You can consider that the force applied to the body and the force applied to the earth are equal and opposite but they are acting on separate bodies and so each body has the same inertial force but the earth has no significant relative acceleration due to its enormously disproportionate mass.

    You can look t the problem is several different way but I have always found it useful to use the proposition that all moments and forces sum to zero and then formulate that equation. Then when you want to find the value of interest you just rearrange the equation to find it.

    Dave
     
  6. Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Dave:

    Since when is an inertial force not a force? Newton stated that for every reaction force there must be an equal and opposite reaction force. These forces may be either static or dynamic and may include inertial forces as your equations demonstrate.

    Unless you can demonstrate to me that an inertial force is somehow not a force, then I would say that Newton's Third Law of Motion still applies and for every force that is applied to an object, there must be an equal and opposite force being applied by another object.

    Here is a nice summary:

     
  7. Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Another example in which a force in addition to the force from the ankle plantarflexors and ground reaction forces on the plantar foot is applied, in this case from the ground on the entire dorsal surface of the body. And I thought my see-saw analogy was a stinker ;)

    So, back to RCSP and the ability of the ankle plantarflexors to lift the right heel without any assistance from other muscles and how that initial acceleration is achieved when the internal ankle plantarflexion moment is equal and opposite to the external ankle dorsiflexion moment because Newton's third law applies... you got to overcome body weight, which in my case is lots of Newtons, how many Newtons can the ankle plantarflexors generate? And how is that initial acceleration achieved?
     
  8. David Smith

    David Smith Well-Known Member

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Kevin, Yes inertia is a force but I was trying to make the point that you can have either perspective. The inertial force is a reaction to acceleration not another force.

    So if I squeeze a ball between both hands it will have two opposing and equal forces acting on it, there is no separate force from inside the ball and the ball is motionless.

    If I throw the ball (horizontal and parallel to the ground) then, all the time ball and hand are in contact, there is a single force from my hand acting on the ball but now because of acceleration there is a force from within the ball equal and opposite to the force from my hand. Of course the inertial force is real but it only appears as a reaction acceleration and also fulfils Newtons 3rd law

    Regards dave
     
  9. Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Newton might disagree, Dave. Hooke and Cauchy explained why, maybe Pascal too if the ball is hollow.


    Assuming the ball and hand are moving forward during the throw, just prior to the release, isn't there more than a single force acting on the ball, that from the resistance from the air and gravity for example?
     
  10. efuller

    efuller MVP

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Yes, the couplets are equal and opposite. But if all forces are equal and opposite then you could never have acceleration because there would never be a net force. It seems that people are having a problem with understanding what I'm saying because they think that all forces must be equal and opposite.

    In Dave's example of throwing a ball, the hand applies a force to the ball and the ball applies a force to the hand. These are an equal and opposite couplet. However, these two forces are applied to different objects. If you examine just the ball, there is only a force from the hand (and gravity and wind resistance), but the force from the hand is the one that is making it accelerate horizontally. When looking at the ball in isolation, there is no equal and opposite force and this makes sense in terms of Newton's second law.

    Eric
     
  11. efuller

    efuller MVP

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Ok, so we will eliminate all other sources. A body in weightless space with the foot on the side of the space ship. The ankle plantar flexors contract, the foot pushes off of the space ship and the body accelerates. No other forces are needed.


    Once ankle plantar flexion has started, the internal plantar flexion moment, or more specifically the plantar flexion moment about the ankle applied by the leg to the foot is not equal and opposite to the external dorsiflexion moment applied by the ground about the ankle joint axis to the foot. It cannot be because of Newton's second law for angular motion. The internal and external moments are not a couplet. One of the couplets is the moment applied by the leg to the foot and the other is the moment applied by foot to the leg. Contraction of the ankle plantar flexion muscles will simultaneously create a moment that will tend to rotate the distal aspect of the foot plantarly and a moment that will tend to rotate the top of the tibia posteriorly. Those are the equal and opposite moments.

    Eric
     
  12. Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    I think we are having a discussion mostly of semantics now and also think that we must be very careful of our terminology or we will all get confused.

    Newton's Third Law of Motion: For every action force, there will be an equal and opposite reaction force. Agreed?

    Inertial force is still a force, even though it involves an acceleration of a mass and not dependent necessarily on gravity. Agreed?

    If you throw a ball with your hand, the force from the ball pressing on the hand must always be equal and opposite to the force from the hand pressing on the ball. Agreed?

    Part of the force from the hand acting on the ball being thrown is coming from the mass of the ball being acted on by gravity with the other part of the force acting on the ball from the hand coming from the inertial force of the ball resisting being accelerated and the wind resistance? Agreed?

    Are we all in agreement now?
     
  13. David Smith

    David Smith Well-Known Member

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Yes this is also true but wind resistance in this case in insignificant (unless the ball is very light and large, something like a beachball) gravity could have an effect but that is why I added "(horizontal and parallel to the ground)" since then there is no influence by gravity on the horizontal motion


    This is quite an important concept to understand, I remember at University and for some time afterwards I was always confused about how it is if all forces are equal that there can be motion. I knew rationally that there is acceleration from an applied force but could not reconcile what I observe with what the theory says, this is a common intuitive stumbling block apparently.

    The summation of all forces are always equal to zero (Newton's 2nd)and yet only unequal forces, i.e. a net force that is not zero, cause acceleration (Newtons 3rd)??

    On the face of it it doesn't make sense and yet it does when we understand the concept of a 'ficticious' yet real force that is only the reaction to, or result of, acceleration.

    Also we can understand the concept of equal and opposite forces if we only apply it to the two bodies acting on one another (Newtons 1st a body will continue on it's course at a constant velocity unless acted upon by another body) So if two bodies act on each other the result is acceleration of both bodies in the direction of the applied and reaction forces but only one unbalanced force acts on each body (ignoring inertial force)

    Sometimes its like trying to imagine the infinite universe you know the theory but the concept makes your head spin:dizzy:


    Regards Dave
     
  14. Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries


    Dave I sure the above makes sense but it not sinking in

    Can you if you have time have another go for the kids in the back row

    Thanks in advance
     
  15. Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Another difficult task is to try and teach these concepts in a clear manner to students so they don't become confused and then, like the discussion we are having currently, it is also difficult to use terminology correctly so that we all don't confuse each other.

    Regarding the concept of accelerations and inertial forces, Albert Einstein, when he was working on his General Theory of Relativity, did a thought experiment to help him better understand the concept of acceleration and gravity. Einstein imagined a person in an elevator car in a weightless environment, in space, and then having a cable tied to the top of the elevator car pulling the elevator with a constant magnitude of acceleration upward (see illustration below). He realized, that to the person inside the elevator in space, that the constant acceleration of the elevator car in a weightless environment would feel exactly equivalent to that person as would the effects of gravitational acceleration.

    In much the same way, we must realize that, if any object with a mass is accelerated, then reaction force must be applied to that object in order to accelerate it. This concept is embodied in Newton's Second Law of Motion, Force (F) = mass (m) x acceleration (a) or F=ma.

    However, we must also realize that no object may apply a force to another object without equal and opposite forces being applied simultaneously between these two objects. This concept is embodied in Newton's Third Law of Motion: for every action there is an equal and opposite reaction.

    Therefore, truly, there are never "unbalanced" forces of one object on another object or a situation where two objects have different action and reaction forces. However, there are plenty of situations where a force (F) acting on an object of mass (m) causes an acceleration (a) of that object (F=ma) so that part of the action-reaction forces generated are due to the resistance of that object being accelerated. This portion of the action-reaction forces which are due to accelerating a mass are what are commonly known as inertial forces. As long as inertial forces are present, then the special circumstances of equilibrium can not be used to predict the forces acting between objects.

    It is for these reasons that I chose, over two decades ago, to use the special mechanical situation of rotational equilibrium to discuss subtalar joint biomechanics. By using an equilibrium situation to discus subtalar joint biomechanics, the mechanical model of the subtalar joint can be significantly simplified so that the goal of a more clear understanding of subtalar joint mechanics may result, without adding the complexity of inertial forces that may prevent some from understanding many important concepts of foot and lower extremity biomechanics (Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989).

    This thread should probably be split off into a new thread: Inertial Forces and Newton's Laws of Motion.
     
  16. efuller

    efuller MVP

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    What really helped me was reading an engineering statics textbook, specifically the section on free body diagram analysis. The first step in free body diagram analysis is defining the body in question. This is where a lot of the confusion comes from. Once you define the body you should only draw in the forces acting on that body. Take a human body in static stance. Which force do you draw to represent ground reaction force? (The force is drawn with arrow pointing upward at the bottom of the foot.) Imagine that person standing on a trampoline. The trampoline springs stretch because of which force(s)? So, if you define your body as the person, then the forces acting on the person are gravity acting downward at the center of mass and force from the trampoline acting upward on the bottom of the foot. There are two different things to look at here. There is equilibrium of the forces acting on the body and then there is looking at the equal and opposite forces and the foot trampoline interface. At rest, the force from gravity acting on the body and the force from the trampoline acting on the body are the same. This is not Newton's third law. This is Newton's second law. F= ma with a being zero. So the net force on the body has to be zero. Newton's third law is also working at the same time so the force acting on the trampoline from the body is equal to the force from the body acting on the trampoline. For Newton's second law we were looking at the forces acting on the body. For Newton's third law we were looking at the interface of two different bodies.

    So, now start with the body falling toward the trampoline. The body is accelerating downward because of the force of gravity is unopposed. The body hits the trampoline and there is now a force from the trampoline applied by the body. Initially, the upward force from the trampoline applied to the body is still less than gravity, so the body will still be accelerating downward, but at slower rate. Eventually, the springs will stretch and start applying more upward force on the body and the force will equal body weight. At this time there is still some downward velocity, but the acceleration is zero. This leads to further stretch of the springs and further increasing force from the trampoline applied to the body. This will continue until the body is fully decelerated and its velocity is zero. However at this time, the force from the trampoline will be greater than the force of gravity and the body will start accelerating upward.

    During that whole time the force from the trampoline acting on the body was variable, but the force from the trampoline acting on the body always equaled the force from the body acting on the trampoline because of Newton's third law.

    Additionally, using inverse dynamics, we could measure the mass of the body and the acceration and then we could calculate the amount of force at any instant in time by using Newton's second law F = ma.

    So, as I said before, you have to carefully label the forces you are analyzing and also know what situation you are analyzing them in. Yes, all the forces acting on a body add up to zero when a body is at rest. That is a special case of Newton's second law and should not be confused with Newton's third law.

    Eric
     
  17. David Smith

    David Smith Well-Known Member

    If you goto this address http://www.foothouse.co.uk/access/inertial-force.htm I have posted up a link to and excel spreadsheet that shows the relationship between inertial force and acceleration when the applied force is constant and the external resisting is varying i.e. not equal to the applied force, in this case it is friction. As friction increases, acceleration and inertial force decrease proportionally and constant to each other i.e. their slopes are parallel. Therefore as frictional force decreases the inertial force increases to maintain the overall zero balance in the summation of forces acting opposite to each other.

    Sorry you can't interact with the spreadsheet as it is read only but I am working on a way to make an interactive link. If you could you would see that however you alter the friction coefficient (and so alter resisting frictional force), mass or applied force the IF and acceleration slopes remain parallel

    Regards Dave
     
  18. David Smith

    David Smith Well-Known Member

  19. musmed

    musmed Active Member

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Dear Simon
    Those who have a forefoot strike, run with an almost straight leg at this moment. The evertor is the short head of the biceps femoris. This is via the fibula. Also the biceps is pulling up the tib posterior by changing the angle of the interosseous membrane and this acting as a synergist to the tib post.

    the other thing with forefoot strike is the flexor digitorum longus is acting as a knee extender.
    Before all get rocking: just assume a sitting position, elevate the great toe, place your fingers on the tibial plateau
    slowly pulls your small toes into the ground,
    note the tibial plateau moves posteriorly as in attempting to produce standing.

    Lousy weather coming.
    Regards
    PauL Conneely
    www.musmed.com.au
     
  20. markjohconley

    markjohconley Well-Known Member

    Re: Podiatrist Recommends Forefoot Striking Versus Orthotics for Treating Running Injuries

    Am enjoying the thread but this would have to be a classic, a pity 'spoonerism' means something else....
     
  21. Dr. Steven King

    Dr. Steven King Well-Known Member

    Mahalo Eric,

    Your quote,
    Ankle plantar flexion is not just the forefoot going down. It is also the rearfoot and leg moving upward with the ball of the foot staying on the ground. When the force from the talus acting on the bottom of the tibia is greater than the force of gravity acting on the rest of the body, the body will accelerate upward and motion is initiatied by the muscles creating tension in the Achilles tendon.

    Eric

    What if we use an external simple machine say the spring orthotic device to lever the rearfoot off the ground what is causing the lift?
    Is it the energy stored in the composite plate or the cantilever of the rigid craddle over a plantar pivot? Most people do not under stand the device i believe you and Craig have a good shot though.

    Mahalo,
    Steve

    Kingetics- Enlightening Your Load...TM
     
  22. efuller

    efuller MVP

    Hi Steve,

    If you have an external machine pushing upward on the heel then you would have two forces that would be creating an upward force on the heel. The plantar flexion moment combined with the ground reaction force on the forefoot will tend to lift the heel up in the air. If the ankle plantar flexors worked faster than the machine pushed then the spring would not contribute to the lift. If the machine was faster than the ankle plantar flexion then it would help the lift and less effort on the ankle plantar flexors would be required. (However, it would take some learning in relatively coordinated individual to make the machine create the optimum motion. In normal every day activities we will need different velocities of ankle plantar flexion. It will be very hard for a machine to help produce those varied velocities. Or, put another way, the output of the machine has to vary with the task. There will be some times during the day that you will want to lower the heel when the machine is trying to raise it. So, there will be times when machine will be working against you. For most people, the normal use of the ankle plantar flexors will produce the motion that they need, because the muscles are directly wired to the brain. The machine isn't. So, the question arises, why would we want this device?

    Eric
     
  23. Dr. Steven King

    Dr. Steven King Well-Known Member

    Aloha Eric,

    1. Bent compressed carbon fiber under tension will return to its non-flexed state faster than any biological system. That is one reason why the AFO's and composite leg prostheses work so well.
    2. A biased catilever "simple machine" will lift the heel at a faster rate than ankle plantarflexion if the ratio is not 1:1.
    3. The Spring Orthotic Device patent awaits your review, please web search it and read it starting from page 35, figure 14 is very helpfull.
    4. There are 85,000 diabetic amputations in the US per year. I believe this system will help off load high pressure areas and reduce shear by mechanical means. Which MAY reduce this very bad number.
    5. IED's cause are causing most of our war casualties, yet the boot makers are still making foam and rubber boots and our troups are wearing blast resistant underwear to limit blast debrie from entering their abdomin and testicles. The most under of our underwear are the boots we wear under our feet.
    5. You have never seen this before take your time, if you have questions please ask them, you will be at the head of the class.

    Mahalo,
    Steve
    Kingetics- Dusting Disabilities...TM
     
  24. Dr. Steven King

    Dr. Steven King Well-Known Member


    Aloha,

    Jeff Root refered us to this website. He said that there may be some good folks who could understand and assist our vetting of this new technology.
    It is important due to the fact that our grant SBIR A11-109 (Advanced Composite Insoles for the Reduction of Stress Fractures.) is being sponcered by the US Department of Defense and the US Army's Medical Research and Materials Command. Peter Cavanaugh's company DiaPedia was the other grantee.

    I belive that point #2 A biased catilever "simple machine" will lift the heel at a faster rate than ankle plantarflexion if the ratio is not 1:1. Is not correct. The rate of heel lift if you take into account excursion will be slower at the heel but the ability to lift a bigger load is enhanced. Again here is why i hope you and Craig and others may help us present this correctly. It confuses many people just ask Simon what he thinks he thinks.:bash:

    Mahalo,
    Steve

    Kingetics- When you come to a fork in the road, Jump Over It...TM
     
  25. I'm not confused in the slightest. I am however, completely unconvinced by you and your apparent knowledge base.

    I think the word you are looking for is "cantilever", by the way. Go look it up.

    Still awaiting a photograph of one of your devices and for you to answer the questions put to you the last time your tried to push your product here, Steven.

    Here's a question: what are the limitations of carbon fibre when used as an orthotic material?
    Here's another: how important is it that energy stored in an insole is returned at the correct time and spatial location during gait?
    Another:
    How does the surface geometry of a piece of carbon fibre influence its load/ deformation characteristics?

    Go back to original thread, I'm sure there were more questions asked of you there which you failed miserably to answer.

    In the meantime, it's my birthday and I'd rather go and stick my gouty 1st MTPJ in a bacon slicer than spend my time reading any more of your made-up drivel.

    Kingetics- When someone asks you a question that you can't answer, ignore it and hope it goes away...TM
    Kingetics- making it up as he goes along, again...TM
    Kingetics- "Like a preacher stealing hearts at a travelling show. For the love of...." http://www.youtube.com/watch?v=UpxI39UD9no&feature=related ... TM
     
  26. timharmey

    timharmey Active Member

    Have a good one
    Tim
     
  27. Simon:

    You are getting to be quite the mature and distinguished man now that you are well into your fifth decade of life. Don't despair, my experience has shown that the mid-50's are still something to look forward to....Happy Birthday.:drinks
     
  28. Cool your boots, I'm only 42 ;) :drinks

    Thanks my friends.
     
  29. And by the way, the bacon slicer says that she is happy for me to do that- boom boom, "A bit of blue. He's blue Derek, he's blue..." in the style of Peter Kay, obviously :drinks
     
  30. Just a spring chicken.....:rolleyes:
     
  31. Yeah, nice... 34 in that picture. Fat and unfit. Since then I've been through the lean and mean period during my rugby renaissance and now back to fat and unfit again following my rugby injury. Never mind. More hair now too.

    And for those of you who have never had the pleasure of a full blown episode of the salmon and trout, I sh!t you not, it's the most painful thing I've ever, ever experienced. And I've had a few kicking's and a selection of broken bones, ligament ruptures, appendicitis etc in my time (I know I've never given birth ladies, but that's nobody's fault, not even the Romans). The classic "it's like a hot corkscrew being inserted into the joint" is an understatement. I'd go more that the joint has turned to molten lava and someone has taken a Black and Decker to it in attempt to extract the molten goo. And no, I can't stand the weight of the bed clothes on my foot right now. And yes, I am cranky.

    The first time I had "the gout" it was a mild attack, this time it's total conflict. Not funny. Bored of it now...:mad:
    AAAAAAAAAAAAAAAAGH.
     
  32. David Smith

    David Smith Well-Known Member

    Dear Dr King

    Your spring orthotic device looks intriguing but there appears to be a flaw in the design.

    Basically from what I can gather by looking at the patent drawings, the device is like a spring assisted see saw. The idea is that the spring assists the see saw to recover its original position after loading the spring. However it appears that what you would gain from the increased moments that rotate the body forward would be negated by the increased moments rotating the body backwards. So you would have greater propulsion but conversely you would have increased braking so overall forward velocity might be constant. Wouldn't this seem to make sense since if you could add some extra propulsive energy into each step then wouldn't you tend to progress at ever increasing velocity until you reached the seed of light?:D

    Regards Dave
     
  33. efuller

    efuller MVP

    I looked at the patent. It appears that you have a carbon plate with essentially a rocker point that appears to be approximately 30% of the foot length from the back of the heel. From the drawings I'm not sure what the design is anterior to that point. Is the front end of the plate fixed? What is it fixed to? Does it move?

    These are important questions for determining if the device would work.

    I'm not sure about your ratio statement. The ratio between what and what?

    Eric
     
  34. Dr. Steven King

    Dr. Steven King Well-Known Member

    Mahalo,
    Dave and Eric and Arena,

    I will concede that the patent was written by a lawyer and is for lawyers. The diagrams believe it or not were drawn by a professional patent draftsman. Since the whole device is an “orthotic” our mechanical and composite engineer and co-inventor Paul Hewitt of Rocket Composites Inc. in Sacramento California helped pen some new terms for the different parts, ie. cradle, spring plate, and pivots. I coined the term Impact Disease since I thought under-mitigated impact may cause more pathology than overuse.

    Dave i have not reached the speed of light yet but i am working on it. You have to do a lot of traveling to try to disprove that you have created the fastest-lightest-safest shoes on the planets...

    The concept is simple and it works well. In the rear foot two counter positioned pivots bend a carbon fiber plate. The components can be "bonded" but not at both contact points, it causes a "warple = warped ripple" in the spring. The contacts points on my 6 mile run this morning along the Kealia Wildlife Refuge were unbonded but mechanically attached. I cover the springs with Kevlar to reduce abrasion to the underlying bidirectional and unilateral carbon fiber layers.

    The system in my best judgment consists of 4 simple machines in a kinetic chain.
    Incline plane-Cantilever-Decline plane-Long Lever
    Each simple machine enhances energy efficiency and work.
    At heel strike the pivot on the cradle flexes the rearward section of the spring into a double bend, this allows for more energy storage than a single flexion (like a coiled spring), this is a incline plane simple machine. It slows down downward velocity and harnesses this energy for later use. It also enhances stability.
    As the ankle/foot plantar flexes the rigid cradle (it must be rigid or you would feel the pivots underneath) cantilevers over the spring pivot, the natural movement of this will lift the heel. This is the cantilever simple machine. This looks really cool on FScan as you see the COM stall a little at heel strike then zoom to the forefoot. The time vs. force graph is flat topped with minimal impact spike.
    The third simple machine i have never heard described before--Decline Plane yet it is the one simple machine we use in our existing footwear (Why do cowgirls have high heel boots?) the 22-12 rule. This allows the COM to increase velocity over a shorter distance.
    The last simple machine is created by the shoe or boot "housing" assisting as a long lever to bend the forefoot spring section. When we attach the system above the ankle we can bend the forefoot spring with greater ease. This worked well when i attached the system to a pair of Ossure Carbon Fiber AFO's and speed walked the Maui Marathon three years ago. This is also important for reducing the forefoot pressure and shear,,,ie healing and keeping ulcers healed, all the bioengineered skin grafts are just punching wind if we cannot reduce shear. It is also a lot of fun on the bottom of a pair of crutches!
    Each component can be changed to better control and guide gait. The spring can be made with custom modulus of elasticity by changing the fiber orientation and thickness (doubling spring thickness height cubes the strength). The pivots can have different radiuses of curvature and height. The location of the pivots can be constructed to alter the flexion moment of the spring. The cradle can be contoured to match the foot surface or posted to create a desired correction. I apply a top cover of 3mm cloth covered neoprene on top of 3mm poron, that’s all the foam in the system.
    It is a lot of fun. I have been able to recover from a nasty Jone’s fracture and complete 3 Maui Marathons, 3 Xterra Championships, and a play whole bunch of Ultimate Frisbee and Tennis.
    Congrats Simon on your 42 trip around the Sun. I empathize with your sore painful toe. I have never had gout but I have had some Royal Pains before and some recently. My best advice is to back away from the Kawa bowl,,,BULA!
    Thank you gentlemen and ladies for considering some new thoughts.
    I am sorry they are not currently for sale, you will need to make your own research pair.
    A Hui Hou,
    Steve
    Kingetics- Greatering Play Time…TM
     
  35. David Smith

    David Smith Well-Known Member

    simon

    is your gout better today?
     
  36. markjohconley

    markjohconley Well-Known Member

    Simon, all the best, something we do have in common.............apart from stunning looks of course.........................wait till it gets into ya' knees lad and you need to "pay a penny"!
     
  37. Here is the paper from Kleindienst on knee joint loading differences between forefoot and rearfoot strikers.
     
  38. Here is the reference for the paper by Kleindienst et al that showed that forefoot striking running showed increased knee abduction moment, increased knee external rotation moment at the end of midstance phase, increased knee internal rotation moment during landing, higher braking and acceleration forces, and increased eversion velocity and rearfoot excursion when compared to rearfoot striking running. I have also included a better quality pdf of the paper than what I provided yesterday.

    Kleindienst FI, Campe S, Graf ES, Witte K: Differences in knee joint loading between forefoot and rearfoot strike patterns. In Frederick EC, Yang SW (Eds). Proceedings 8th Footwear Biomechanics Symposium, pp. 129-130, 2007.

     
  39. Dr. Steven King

    Dr. Steven King Well-Known Member

    Aloha,

    Kevin keep ignoring this, perhaps it will go away. I came to you in good faith two years ago with this and you would not help because we could not pay you. WE still cannot pay and for that i am sorry. Dr. Cavanaugh said he did not have the "Bandwigth" to help then he applies for the same grant we wrote? Dr. Harkless has seen the device and stated he did not understand the biomechanics and maybe he would send it to Dr. Christiansen, if he remembered. Dr. Beth Jarret will not respond as well. We must be on the right track then if the guru's of our profession are unable to follow our new trail.

    When prior students of biomechanics come forward with new idea's to solve some of the problems we face everyday what do we do? What should we do?

    Mahalo,
    Steve
     
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