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Biotensegrity and Mechanical Analysis

Discussion in 'Biomechanics, Sports and Foot orthoses' started by efuller, Jun 3, 2008.

  1. efuller

    efuller MVP


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    Part I critique of mechanical analysis

    Thanks to Stanley for posting this paper on biotensegrity.

    http://www.intensiondesigns.com/itd-...rs/paper5.html

    Since we have been having a hard time defining biotensegrity its nice to have an article to refer to evaluate the concept.

    Minor point: No author listed.

    "If the present paradigms of Newtonian based biomechanics hold true, then the calculated forces needed for a grandfather to lift his three year old grand child would crush his spine, catching a fish at the end of a fly rod will tear the angler limb from limb, and the little sesamoid bones in our feet will crush with each step"​

    There is an error in understanding mechanical analysis. When you create a mechanical model, you test it against reality and discard the model if it does not predict reality. If the forces of fly fishing are calculated to be to high to be possible you discard the assumptions of that model and recheck the calculations. You don't discard the whole paradigm.

    "According to conventional wisdom and present paradigms, the human spine and skeleton behaves like an architectural column, a tower of blocks, and supports the body weight as a pillar supports a building.1"​

    You take a faulty mechanical analysis and then say the whole of mechanics is wrong. The article goes on how conventional wisdom about the spine being a mechanical column is erroneus. Yes it is erroneus to assume the spine is a column, but an engineer would not consider it one.

    "It's not that Newtonian mechanics is wrong; it is that the set of assumptions is wrong. A similar problem arises in geometry. Euclidean geometry tells us that parallel lines never meet. However, on the surface of the earth, lines of longitude are parallel, yet they meet at the North and South Poles. Euclidean geometry is not wrong; it is just that we make a different set of assumptions in order to describe the geometry of the earth. It turns out that Euclidean geometry is a special case geometry where the curvature of the plane is zero degrees. Spherical geometry is non-Euclidean geometry. It appears that bioarchitecture requires non-Newtonian and non-Hookean mechanical thinking that are more adaptable to life forms than are Newtonian and Hookian models"​

    "It appears" It appears that the authors are claiming that biological structures don't behave by Newton's Laws. Now here is where you need some evidence.

    :pigs:

    "The free body diagram has been the reductionist approach to biomechanical modeling. Each segment is modeled in isolation. ....

    some cut and then the beginning of the critique of free body diagram of forearm and upper arm and muscles.

    In the arm, the biceps is a two joint muscle and crosses the glenohumeral joint in addition to the elbow joint. As the biceps crosses the glenohumeral joint, that creates a moment at the shoulder. The glenohumeral joint is stabilized be antagonist muscles, such as the triceps, which is a muscle that extends the elbow and it must then enter into a feedback loop with the biceps. Holding a weight in the hand requires the use of the wrist flexors and finger flexors. They also cross the elbow joint and will create moments that need to be counterbalanced with the triceps, and so on. The glenohumeral joint connects to the axial skeleton through the scapula, which suspends from the chest wall by muscles that must also enter into the feedback loop. It is clear that there are no sharply defined segment boundaries. In the scapulo-thoracic complex, no rigid structure that can act as a fulcrum as there is no bone-on-bone contact. Without a fulcrum, there is no lever. Any moments passed from arm to axial skeleton is only accomplished through the tension of muscles. You can only pull with a muscle, it cannot act as a rigid lever."

    Faulty mechanical analysis. The authors are essentially saying that you can't do a free body diagram analysis of the arm and fore arm because you are ingoring the shoulder and this is a problem because the soulder does not have a fulcrum. The whole point of free body diagrams is that yes you can ignore things outside of your defined system if you know or can predict the forces from them. In the case of the upper arm, if you know that the upper arm is not accelerating relative to the trunk then you know it is in equilibrium, and then can predict the forces acting on the shoulder.

    Now the shoulder is an interesting thing and I have not thought about the anatomy of the bench press much. Howerver, it is possible to create that moment/motion without a boney fulcrum. It could be done with a force couple of muscles. Pec major attached a ways down the shaft of the humorus and muscles of the shoulder girdle pulling the head of the humorus in the opposite direction of the pull from pec major would create a force couple without a bony fulcrum. You can explain these things with mechanical analysis.

    End of part I critique

    Cheers,

    Eric
     
  2. efuller

    efuller MVP

    Part II

    Critique of biotensegrity as stated in
    http://www.intensiondesigns.com/itd-...rs/paper5.html

    Alternative models
    The authors propose using the mechanical model of a truss to explain the spine. Yes, this is better than the column.

    "Three dimensional, or space trusses, are some combination or permutation of the three regular polyhedrons that are fully triangulated, the tetrahedron with four triangulated faces, the octahedron with eight and icosahedron with twenty (Figure 4). The icosahedron has some distinct advantages in biologic modeling. It has the largest volume for surface area, an economy of resources, and has the ability to be close packed to fill space."​

    But, where is the comparison to reality.. Then there is a long discussion of polyhedrons without any reference to anatomical structures. What anatomical structures are polydrons packed together?

    "One of the more familiar tensegrity structures is the wire spoke bicycle wheel. A wagon wheel vaults from spoke to spoke, bearing full load on each spoke in turn. It needs thick spokes and a thick rim to support compressive loads. The wire wheel has a compression-loaded hub, which is separated by multiple tension-loaded spokes from its compression-loaded rim. The spokes are under constant, equal tension."​

    The bicycle wheel is very interesting, but on a loaded bicycle the spokes on the bottom side do behave as compression members. This can be verified by plucking the spoke in loaded and unloaded condition. There is a lower tone of the plucked spoke when it is loaded. See the Bicycle Wheel by Jobst Brandt. The concept is pretensioning. The spoke goes from one amount of tension to a lesser amount of tension when it is compressed.

    "Some of the unusual mechanical properties of icosahedral trusses, particularly the internally vectored endoskeletal icosahedrons, are that they have a nonlinear stress-strain curve which is considered by Gordon12 to be the essential element of biologic materials."​

    They are similar so they must be the same?

    "Let us assume human, whole body modeling, as tensegrity structures. Changing muscle tone would alter the body posture, from recumbent to standing. Once the tone is set, no further muscle activity is necessary to maintain that posture, as the truss is stable. For instance, during quiet standing, no additional muscle contraction would be necessary and the EMG would not record any significant activity. Muscles act in unison, rather than antagonists, as they are the tension elements of the truss."​

    Yes altering muscle tone will alter body posture. If we were capable of standing so that our center of mass was over our center of gravity, and there was no wind then yes we could stand without using the muscles of the lower leg. During standing there is sway and when you sway forwad you use your Gastroc and soleus to shift your center of pressure forward, so that you can sway backward. If your center of mass goes to far back then you use the anterior leg muscles to shift your center of pressure more posterior than your center of mass. These muscles have opposite functions. In my book they are antagonists. The EMG recordings of standing individuals will show changes in EMG activity and hence changes in muscle tension. Animals are living things and have to respond to their environment. They cannot be static polyhedrons.

    "A model for this is Snelson's "Needle Tower" (Figure 9). In it, the compression elements are enmeshed in a fractal construction of tensegrity icosahedrons. Compression elements "float" in the interstices of tension wires."

    A model for the spine. So which anatomical structures are the floating compression elements. Which structures are the tension elements. Where is the analysis and measurments that shows that the anatomical tension elements have forces in the correct direction to lift apart the compression elements.

    If the lumbar vertebra are held apart by tension lements then the tension in the ligaments or muscles would have to be constantly greater than the weight of the body above that particular lumbar vertebra. Are these ligaments that highly strung? Do they prevent pressure in the intravertebral disks? Where is the comparison of this model to reality?


    "CONCLUSION

    Others have challenged the perceived inadequacies of the current total human body models and several issues are raised.19,20 Biotensegrity, the application of Fuller's tensegrity concepts to biologic structure and physiology, apparently can be used to successfully model the spine and other organ systems. In this system of total body modeling, the limbs are not an assemblage of rigid body segments. They are semi-rigid non-linear, viscoelastic bony segments, interconnected by non-linear, viscoelastic connectors, the cartilage, joint capsules and ligaments and with an integrated non-linear, viscoelastic active motor system, the muscles and tendons and connective tissue. The visceral organs integrate structurally and physiologically into the same system. There are no limb segment boundaries and the smaller bones and joints of the hands and feet fully integrate into the mechanical model. The spine is a tensegrity tower that integrates with the limbs, head and tail and to the visceral system, as well. A change of tension anywhere within the system is instantly signaled to everywhere else in the body and there is a total body response by mechanical transduction. The structure works equally well right side up, upside down, in sea, land, air or in space. It resolves many of the inadequacies of present models. "​

    :pigs:

    If there is a better paper on tensegrity than this one bring it on.

    Cheers,

    Eric Fuller
     
  3. Admin2

    Admin2 Administrator Staff Member

  4. kevin miller

    kevin miller Active Member

    To all,

    In response to Eric's post, I offer a private e-mail from Dr Steve Levin to me. I thought he made excellent points and I asked if I might post them. With his permission......

    Regards,
    Kevin M


    My quotes are green, Eric is blue, my comments are black. (I put Eric's comments in itallics -KM)


    "It's not that Newtonian mechanics is wrong; it is that the set of assumptions is wrong. A similar problem arises in geometry. Euclidean geometry tells us that parallel lines never meet. However, on the surface of the earth, lines of longitude are parallel, yet they meet at the North and South Poles. Euclidean geometry is not wrong; it is just that we make a different set of assumptions in order to describe the geometry of the earth. It turns out that Euclidean geometry is a special case geometry where the curvature of the plane is zero degrees. Spherical geometry is non-Euclidean geometry. It appears that bioarchitecture requires non-Newtonian and non-Hookean mechanical thinking that are more adaptable to life forms than are Newtonian and Hookian models"


    "It appears" It appears that the authors are claiming that biological structures don't behave by Newton's Laws. Now here is where you need some evidence.


    Just for starters; Blood is a non-newtonian fluid, bone, cartilage, fascia and essentially all biologic tissues have nonlinear stress/strain curves and, therefore, are non-hookean/non-Newtonian. Body tissues are emulsions/colloids/foams and follow the laws related to foams, which are nonlinear/non=Newtonian/non-hookian.


    "The free body diagram has been the reductionist approach to biomechanical modeling. Each segment is modeled in isolation. ....


    some cut and then the beginning of the critique of free body diagram of forearm and upper arm and muscles.


    In the arm, the biceps is a two joint muscle and crosses the glenohumeral joint in addition to the elbow joint. As the biceps crosses the glenohumeral joint, that creates a moment at the shoulder. The glenohumeral joint is stabilized be antagonist muscles, such as the triceps, which is a muscle that extends the elbow and it must then enter into a feedback loop with the biceps. Holding a weight in the hand requires the use of the wrist flexors and finger flexors. They also cross the elbow joint and will create moments that need to be counterbalanced with the triceps, and so on. The glenohumeral joint connects to the axial skeleton through the scapula, which suspends from the chest wall by muscles that must also enter into the feedback loop. It is clear that there are no sharply defined segment boundaries. In the scapulo-thoracic complex, no rigid structure that can act as a fulcrum as there is no bone-on-bone contact. Without a fulcrum, there is no lever. Any moments passed from arm to axial skeleton is only accomplished through the tension of muscles. You can only pull with a muscle, it cannot act as a rigid lever."


    Faulty mechanical analysis. The authors are essentially saying that you can't do a free body diagram analysis of the arm and fore arm because you are ingoring the shoulder and this is a problem because the soulder does not have a fulcrum. The whole point of free body diagrams is that yes you can ignore things outside of your defined system if you know or can predict the forces from them. In the case of the upper arm, if you know that the upper arm is not accelerating relative to the trunk then you know it is in equilibrium, and then can predict the forces acting on the shoulder.

    Eric misses the feedback loop that prevents a state of equilibrium. It is impossible to ignore things outside the system when there is a feedback loop. What is happening inside the system depends on what is happening outside the system that depends on what is happening inside the system and -- round and round. There are several articles in the biomechanics literature that point out the fallacy of free body diagrams. Have Eric look them up, (I am not going to do all the work for him).


    Now the shoulder is an interesting thing and I have not thought about the anatomy of the bench press much. Howerver, it is possible to create that moment/motion without a boney fulcrum. It could be done with a force couple of muscles. Pec major attached a ways down the shaft of the humorus and muscles of the shoulder girdle pulling the head of the humorus in the opposite direction of the pull from pec major would create a force couple without a bony fulcrum. You can explain these things with mechanical analysis.


    Without a fulcrum, there is no lever. If you are force coupling tension elements you are getting into tensegrity.


    The authors propose using the mechanical model of a truss to explain the spine. Yes, this is better than the column.



    "Three dimensional, or space trusses, are some combination or permutation of the three regular polyhedrons that are fully triangulated, the tetrahedron with four triangulated faces, the octahedron with eight and icosahedron with twenty (Figure 4). The icosahedron has some distinct advantages in biologic modeling. It has the largest volume for surface area, an economy of resources, and has the ability to be close packed to fill space."


    But, where is the comparison to reality.. Then there is a long discussion of polyhedrons without any reference to anatomical structures. What anatomical structures are polydrons packed together?

    Let's start with the cell which is a polyhedron, and as you pack polyhedrons {cells) you get more polyhedrons. Eric has to read Tom Flemons article on the Geometry of Anatomy on his website. Eric doesn't seem to know the definition of 'polyhedron'. Go to Wikipedia/regular polyhedra/polyhedra in nature. Cells are not 'round', as they flatten when pressing against an adjacent cell, therefore, they are polyhedrons. We then have to get into closest packing, etc..


    The bicycle wheel is very interesting, but on a loaded bicycle the spokes on the bottom side do behave as compression members. This can be verified by plucking the spoke in loaded and unloaded condition. There is a lower tone of the plucked spoke when it is loaded. See the Bicycle Wheel by Jobst Brandt. The concept is pretensioning. The spoke goes from one amount of tension to a lesser amount of tension when it is compressed.

    Not according to Fuller, (the other Fuller). Brandt is wrong. When perfectly tuned - the tension is constant. On a similar note -- when you load a pneumatic tire, does the pressure in the tire increase? (No it does not. I'll take all bets on this one)!


    "Some of the unusual mechanical properties of icosahedral trusses, particularly the internally vectored endoskeletal icosahedrons, are that they have a nonlinear stress-strain curve which is considered by Gordon12 to be the essential element of biologic materials."


    They are similar so they must be the same?


    No, but if they are dissimilar, if they do not have nonlinear properties, then they cannot be used to model biologic material. Endoskeletal icosahedrons can be used, can eric give examples of structures that can be used for modeling and are nonlinear? Cubic systems used in finite element modeling are linear and so are tetrahedral models.


    Yes altering muscle tone will alter body posture. If we were capable of standing so that our center of mass was over our center of gravity, and there was no wind then yes we could stand without using the muscles of the lower leg. During standing there is sway and when you sway forwad you use your Gastroc and soleus to shift your center of pressure forward, so that you can sway backward. If your center of mass goes to far back then you use the anterior leg muscles to shift your center of pressure more posterior than your center of mass. These muscles have opposite functions. In my book they are antagonists. The EMG recordings of standing individuals will show changes in EMG activity and hence changes in muscle tension. Animals are living things and have to respond to their environment. They cannot be static polyhedrons.

    Huijing has clearly shown that all muscles are connected - there are no agonists - antagonists. See also: Turvey. Muscles can only pull down! Contracting the gastroc would force the knee to flex and the body to collapse. A falling body can only be stopped by an external force. Any muscle within the falling body would be useless to keep it from falling.


    If the lumbar vertebra are held apart by tension lements then the tension in the ligaments or muscles would have to be constantly greater than the weight of the body above that particular lumbar vertebra. Are these ligaments that highly strung? Do they prevent pressure in the intravertebral disks? Where is the comparison of this model to reality?


    Flemons estimates the total tension in the body to be close to infinite, it is just divided into an infinite # of smaller units. It is the difference of a multi-stranded steel cable and a single strand.


    If there is a better paper on tensegrity than this one bring it on.


    If he wants more, read the other papers, Tom Flemons' paper, my DVD, and, best of all, invite me to speak and challenge me directly.


    Steve
     
  5. efuller

    efuller MVP

    There are many non biologic materials that have non-linear stress strain curves. It does not follow logically that non linear stress strain curves means that the material is non newtonian.

    Why can't you model bone as a rigid body. Yes, it bends a little, so does steel. Tendon can be modeled as a tension structure. A rope can be modeled as a tension structure. Why are biological tissues immune to the laws of physics? I will agree that fluids cannot be modeled as rigid structures, nor as tension elements.



    How does a feedback loop prevent equilibrium. The definition of equlibrium that I'm using is the engineering definition where a system is not accelerating and the net moment and net force acting on it is zero.

    You can go into any college bookstore that has engineering classes and buy a textbook that will describe free body diagram analysis. Is Steve saying that all of these books are wrong? Are all the engineers in the world being mislead?

    Or is this the biological materials don't obey the laws of physics argument? Can pigs fly? Why don't they fly? :pigs:

    Just because someone tries to model blood as a rigid body, does not mean that all of mechanical analysis does not work on biological tissues.

    I went to pub med and looked up fallacy of free body diagram and faulty free body diagram and got no results. Perhaps, Steve could help me find these articles.


    After thinking about this some more, I realized that you can have a tension fulcrum. You don't need a bony fulcrum. A classic tension fulcrum is a hanging balance. The upward force from the string tied to the middle of the arm of a hanging balance provides a fulcrum for the loads on either end of the arms of the balance. So, if you don't look for a bony fulcrum in the shoulder, you will not see it. However, that does not mean that it is not there.

    Let's start with bone which is a matrix of collegen and calcium hydroxyapetite crystals that have osteoclasts, osteoblasts, and osteocytes imbedded within in it. The individual cells make and remodel the bone, but the mechanical characteristics of the cell do not have anything else to do with the material properties of the bone. The crystals provide reistance to compression and the collegen provides resistance to tension. I don't see what this has to do with polyhedrons. How does the cellular structure have anything to do with mechanical properties of the bone.

    Brandt is right. I checked it, while applying a load to the seat of the bicycle. You pluck the spokes with and without load and tone created by the spokes changed. When the spokes are tighter, there is a higher pitched tone. When there is less tension in the spokes there is a lower pitched tone. I also verified this by tightening the spokes and plucking.

    I would rather ride a bike with wheels built by Jobst Brandt than on wheels built by Buckminster Fuller.

    I'm not quite sure what he means by non linear. Is he referring to stress/ strain curves? I'm not understanding the logic of the above point. Kevin, could you send it back to Steve and have him explain it further?

    All muscles are connected. Is that why some people have trouble walking and chewing gum at the same time? How come others can walk and chew at the same time?

    Muscles can only pull down??? Muscles pull an equal amount on both their ends.

    The knee will not flex when the gastroc contracts if the quads are contracting creating an extensor moment.

    Yes, a human body falling from a height will only be stopped by an external force. Ground reaction force is an external force. Once we have ground reaction force we have to balance with muscle contraction.

    And the ligaments are able to handle nearly infinate tension.:wacko: So which ligaments are you referring to when you make the above statement?

    Or, Steve could invite me to speak and I can bring my powerpoint and cool laser pointer and he can challenge me directly. Or we can discuss on the forum. Apologies for some of the tone. It bothers me when someone who does not know me implies that I don't know something.

    Cheers,

    Eric
     
    Last edited: Jun 14, 2008
  6. kevin miller

    kevin miller Active Member

    Eric,

    Dr. Levin will see your response and I will gladly let him reply.

    In reference to one of your statements: Why can't you model bone as a rigid body. Yes, it bends a little, so does steel. Tendon can be modeled as a tension structure. A rope can be modeled as a tension structure. Why are biological tissues immune to the laws of physics? I will agree that fluids cannot be modeled as rigid structures, nor as tension elements.

    Quickly look up two topics: Plastic deformation and Wolf's law. They reply to viscoelastic structures of which bone is both. The fact that bone is a viscoelastic structure refutes your entire line of thought because it can be modeled as a fluids. Oh.... trabecular patterns are polyhedral.

    Kevin
     
  7. kevin miller

    kevin miller Active Member

    Eric,

    Followig is Dr Levin's reply. I believe I have your comments in itallics. Pardon me if I get something wrong:

    There are many non biologic materials that have non-linear stress strain curves. It does not follow logically that non linear stress strain curves means that the material is non newtonian.

    Newtonian implies hookian -for every action there is an equal and opposite reaction - nonlinear structures do not have equal reactions, the s/s curve is variable with load and time (viscoelastic).


    Why can't you model bone as a rigid body. Yes, it bends a little, so does steel. Tendon can be modeled as a tension structure. A rope can be modeled as a tension structure. Why are biological tissues immune to the laws of physics? I will agree that fluids cannot be modeled as rigid structures, nor as tension elements.

    Bone does not behave like steel. It has a nonlinear s/s curve, is orthotropic, and is more like a stiff, starched shirt than a suit of armor. It is a stiff foam, like auto bumpers.
    All tissues in the body are foams, colloids or emulsions, not elastic or fluid, and the mechanical laws that apply are that of foams - see 'Universal Foam'- Sidney Perkowitz. The same can be said of tendons, they are foams and have nonlinear mechanics.


    How does a feedback loop prevent equilibrium. The definition of equlibrium that I'm using is the engineering definition where a system is not accelerating and the net moment and net force acting on it is zero.

    Feedback loops create a state of non-equilibrium- The structures are interdependent and always in a state of flux. Any change in one creates a change in the other and back and forth And the net forces are not zero, they oscillate back and forth.


    You can go into any college bookstore that has engineering classes and buy a textbook that will describe free body diagram analysis. Is Steve saying that all of these books are wrong? Are all the engineers in the world being mislead?


    Free body diagrams can work when there are no feedback loops.


    Or is this the biological materials don't obey the laws of physics argument? Can pigs fly? Why don't they fly?

    Of course they obey the laws of physics -just not your laws, or as you interpret them. By following the the laws of Newtonian physics, bumble bees can't fly, and dinosaurs never could have existed. “Einstein may have changed the way in which we view the universe, but our view of the human body is still essentially Newtonian.” — Peter Cavanagh 1


    Just because someone tries to model blood as a rigid body, does not mean that all of mechanical analysis does not work on biological tissues.


    Read my article on 'Slippery Slope' (on my website) just to see how physics is misused by those who should know better.




    I went to pub med and looked up fallacy of free body diagram and faulty free body diagram and got no results. Perhaps, Steve could help me find these articles.



    Try: Neuromusculoskeletal control systems modeling--A critical survey of recent developments
    Hatze, H.
    National Research Institute for Mathematical Sciences, CSIR, Pretoria, South Africa; and a lot of other stuff Hatze wrote, particularly his later writings, including letters to the editor. There are other authors, too.. Hatze died a few years ago, but he was one of the worlds most respected biomechanics.




    After thinking about this some more, I realized that you can have a tension fulcrum. You don't need a bony fulcrum. A classic tension fulcrum is a hanging balance. The upward force from the string tied to the middle of the arm of a hanging balance provides a fulcrum for the loads on either end of the arms of the balance. So, if you don't look for a bony fulcrum in the shoulder, you will not see it. However, that does not mean that it is not there.


    We are talking pendulums here. Argue this one with Archimedes.


    Let's start with bone which is a matrix of collegen and calcium hydroxyapetite crystals that have osteoclasts, osteoblasts, and osteocytes imbedded within in it. The individual cells make and remodel the bone, but the mechanical characteristics of the cell do not have anything else to do with the material properties of the bone. The crystals provide reistance to compression and the collegen provides resistance to tension. I don't see what this has to do with polyhedrons. How does the cellular structure have anything to do with mechanical properties of the bone.


    This one requires an (minimal) understanding of hierarchy, systems science, chaos theory, fractals and evolution. All of them, and their relevance, are touched on in my slide talks. Cell mechanics and organism mechanics are one and the same, and I can show you why.


    Brandt is right. I checked it, while applying a load to the seat of the bicycle. You pluck the spokes with and without load and tone created by the spokes changed. When the spokes are tighter, there is a higher pitched tone. When there is less tension in the spokes there is a lower pitched tone. I also verified this by tightening the spokes and plucking.


    I would rather ride a bike with wheels built by Jobst Brandt than on wheels built by Buckminster Fuller.


    Are you saying that the bottom spoke is under compression or just less tension? If the latter, then BF is correct, it just that we are imperfect in balancing all the tension in the spokes.




    I'm not quite sure what he means by non linear. Is he referring to stress/ strain curves? I'm not understanding the logic of the above point. Kevin, could you send it back to Steve and have him explain it further?

    Stress/strain curves. (Steve is refering to a simple stress strain curve of a biological, viscoelastic structure like a ligament, tendon, bone, etc.)

    All muscles are connected. Is that why some people have trouble walking and chewing gum at the same time? How come others can walk and chew at the same time?


    See Hatze,Turvey, Huijing, Maas and some other very smart people.


    Muscles can only pull down??? Muscles pull an equal amount on both their ends.


    Yes, but one end is anchored to the ground by gravity. The gastroc can only pull down when the foot is on the ground.


    The knee will not flex when the gastroc contracts if the quads are contracting creating an extensor moment.


    Now you are talking tensegrity (almost). You are also talking feedback loops, inverse dynamics, etc. What happens to the pelvis when the quad contracts? If the foot is on the ground - the hip must flex and what stabilizes that? If the hamstrings contract, that would flex the knee - and round and round.


    Yes, a human body falling from a height will only be stopped by an external force. Ground reaction force is an external force. Once we have ground reaction force we have to balance with muscle contraction.



    If you are balancing muscle contraction in the total organism then you would need a construct like biotensegrity to do it. The body is accelerating to the center of the earth a speed of 9.8M/sec/sec. Once the gatroc contracts -everything from the knee up is part of the falling body and no muscle in the body above the knee can keep it from falling - unless it is part of biotensegrity structure or some other- as yet undiscovered, mechanism.


    Or, Steve could invite me to speak and I can bring my powerpoint and cool laser pointer and he can challenge me directly. Or we can discuss on the forum. Apologies for some of the tone. It bothers me when someone who does not know me implies that I don't know something.


    If it offended you, I apologize for the tone of my last remark, but the conventional mechanics is out there, and has been for over 300 years and, if one is willing to look closely, there are many unsolved problems with the underlying theory as it applies to biologic structures. Biotensegrity is a new concept that challenges old ideas. I think it deserves a hearing and would be best done in a face-to-face presentation as a lot of this stuff needs visual enforcement. I expect a healthy skepticism, but also a fair hearing. Flying pig images don't exactly convey an open attitude or a scientific inquisitiveness. It it is those images that have set the tone of this discussion.


    Steve
     
  8. David Smith

    David Smith Well-Known Member

    Erid

    I believe this is a case of the 'paradox of tautological systems'. (I think that phrase is accurate)

    In science we have conventions that define our system and those concepts are axioms and statements of truth that most people take as unfalsifiable. This is a paradox in itself since if we accept that all scientific theory must be falsifiable then axioms cannot be scientific (my understanding of Karl Popper ' The logic of scientific discovery'). However since working with no reference point is chaotic then we choose to accept axioms as truth.

    The convention most of us like to put our faith in is Newtonian mechanics, even tho we know that they are not unfalsifiable and have been falsified, in theory, by quantum mechanics. However for the purposes of mechanics in our earth bound gravitational field this convention works well and usefully.

    If someone chooses not to follow these axioms then argument becomes moot since the tautology is broken. If we allowed the changes to the axiom then the entropy is exposed and the system would decay. That is not possible to accept and so we can allow no changes.

    Even small changes like "Newtonian impliese Hookian"cannot be tolerated since Newton did not say that all materials have a linear displacement when acted upon by a force. Hook made this assumption for useful convenience. If we accept that quote, then this would mean that Newtonian mechanics cannot apply to non linear materials and the system is open to uncertainty.

    One can either accept Newtonian mechanic as an axiom or propose some other system but not consider both at once.
    Two systems cannot exist symbiotically, one must accept one or the other and interrelated speculative argument is just a waste of time.

    However before one disregards the status quo it seems reasonable that one should have a theory with its own axioms to support the latter and replace the former. To have a theory alone is inconsequential at worst and metaphysical at best.

    It may be worth noting though that metaphysics can be the birth place of new realities. Since it is only our minds that define our world and the nature of being and nature since no natural laws of its own then imagination spawns new definition.

    Theories, however, without axioms are like travelling with no reference point and doomed to aimless wandering, confounding uncertainty and premature decay.

    Just my thoughts, if they make sense to anyone :wacko:.

    Cheers Dave
     
  9. David Smith

    David Smith Well-Known Member

    Sorry to post the same thing twice but this is just wrong.

    All forces have equal and opposite reaction that is how they exist and they exist because of that definition. The existance of force does not depend on the material characteristics it acts on. The material characteristics will only change force charcteristics. The non linear, even visco elastic, material can be characterised using dash pot and spring configuration models. Assumptions of linearity reduce the model effectively to one spring, which makes calculation of deformation much more convenient and often useful if not entirely accurate in some materials.

    If you do not accept this then what convention can you replace it with?

    Can you show evidence of unequal reation to a force action?

    Dave
     
  10. kevin miller

    kevin miller Active Member

    David,
    I am not answering for Dr. Levin, but what I think he was refering to is the characteristic of a viscoelastic material to transfer and or disipate some engergy. You can measure this hysteresis in calories or joules. (as heat) Eg. Newton: I puch a wall with 50 newtons of force, and I get that back so I break my hand. OR I puch a big blob of silly putty which dissipates so force and rapidly slows my hand down. My hand is not broken.

    In tension, a not stretchable rope returns and equal and opposite tension. A ligament does not. It disipates the toe region force as histeresis while force greater than toe region produces creep or plastic deformation.

    In other words, he is saying that straight Newtonian phisics does not describe the function of a viscoelastic material.
    Kevin M
     

  11. Robert Hooke and Sir Isaac Newton were both English scientists and they knew each other very well, but argued with each other until their death. I'm sure we aren't at all like them.:rolleyes:

    Viscoelasticity does not imply non-Newtonian behavior. As David said, viscoelasticity simply implies a time-dependent nature to the load vs deformation curve of a material and has been modeled for decades using Newtonian mechanics using spring-dashpot combinations. Just because a material stetches or compresses over a given period of time does not mean it does not follow Newtonian behavior. Newton's laws still apply whether the force applied to a material deforms it in .01 seconds or takes 10 seconds to deform it. "For every action there is an opposite and equal reaction" still applies for viscoelastic materials including bone, cartilage, ligament and tendon.

    Modelling bone as a rigid body has been used for at least the past half-century in biomechanics and is a very useful approximation of reality to allow fairly accurate calculations to be made in numerous scientific studies. Yes, bone is not steel, and steel is not diamond either. All material deform under load, but the relative deformations of bone under weightbearing loads is so small that using the rigid body approximation is valid in most biomechanics application.

    I have never heard of ligament being described as a foam....I guess all the other researchers in ligament histology, physiology, and biomechanics better rewrite their research papers since this is a new one on me. Could I spray some ligament on my face in the morning to help me shave more closely?:rolleyes:
     
  12. efuller

    efuller MVP

    Steve (Through Kevin M.) I apologize for my initial tone with the flying pigs. I should have realized the original author of the piece listed at the top of the forum could have replied. I wish to restart the tone of the debate on the validity of tensegrity.

    I agree with Dave's point here. No matter what you push on, it pushes back. You can push on air, water, rock etc. and they all push back against you with an equal and opposite reaction. If this were not true parachutes could not work. We would not be able to swim etc.

    I did not say that bone behaves exactly like steel. Bone bends when placed under stress. I can see modeling the calcaneus with its cancelous bone as a stiff foam. I can also see modeling it as a rigid body. Why can't you model a stiff foam (if it is stiff enough in relation to the forces applied) as a rigid body. Why does an object have to have a linear stress strain curve to be modeled as a rigid body?

    Can you give an example of a feedback loop where you have constant oscilation without additional input of energy. It sounds like you are talking about perpetual motion. I'm not understanding what you mean by a feedback loop.


    I don't understand the Peter Cavanagh quote in relation to your argument. I also do not accept the premise that we cannot explain, with physics, how a bumble bee flies. Bees have wings, wings push against air, air pushes against wings lifting the bee. Tell me what is wrong with my interpretation. Much of the criticism, to this point has been saying that Newtonian physics can't be applied to non-linear type materials. Why can't Newtonian physics be applied to non-linear materials?


    Could you expand and explain how what I said is talking about pendulums?

    Was I not clear on what I meant by a hanging balance? A hanging balance is a rod with a string attached at the center. Load can be applied at either end of the rod. The rod (balance) will rotate downward on the side with the larger load. It will rotate about the thread from which it is suspended and this will be the fulcrum of the lever.

    This point was in relation to the shoulder not having a fulcrum. It can have a tension fulcrum.



    Send me your powerpoint. fullerpod@lmi.net

    I'd really like to see how you explain the histology.


    The comparison is between the wheel turned sideways to gravity where all the spokes on one side of the wheel are perfectly tuned and equally tight, versus a wheel attached to a bicycle with a 200 lb rider on it. Sideways unloaded wheel: you pluck all the spokes and they have the same tone. Loaded wheel: the spokes on the bottom have a lower tone when plucked than the spokes above the hub. This is a sign that there is less tension in the previously perfectly balanced tension in the spokes.

    So, I disagree that the tension is imperfectly balanced.


    Person standing, Gastroc is stimulated. What is the direction of pull of the tendon acting on the calcaneus?

    Now you are talking biomechanics. The brain sends a signal for the muscle to cause it to contract. The muscle generates force, which creates moments at joints. The brain sends signals to each of the muscles that are required to get the desired motion. Different muscles are activated if the brain chooses to do a forward flip as opposed to a backward flip. It doesn't really go round and round unless the brain chooses to.

    I guess that is a feedback loop. But, it is certainly not a reflexive feedback loop.



    A few years back I attended a biomechanics conference where they explained, with mechanics how a lizard could run on water. First, you start with the lizard that runs on water. Then you take measurements of the size of the feet, the speed of the feet in the water and then make some assumptions. e.g. the foot of the lizard moves a column of water at the measured speed and calculate the force needed to move this column of water. Then compare this force of the mass and acceleration of the lizard. If the numbers don't add up you recheck your measurements, recheck your assumptions and redo the calculations. The presenters did this and could explain with physics how the lizard could run on water.

    You can say we can't show how a bumble bee can fly with physics. And I can reply the calculations were not done correctly because the bumble bee does fly.

    How does tensegrity explain bumblebee flight?

    Steve, What is your definition of tensegrity? Is it the one where there is discontinuous compression? Are tension units used to hold the compression units apart? Is it possible to measure the tension in tension units of a tensegrity structure? Do the ligaments of the spine have enough tension in them to hold the vertebra apart? How can we test a spine to see if it is a tensegrity structure?

    One of the reasons that I am skeptical of tensegrity is that I don't see it as a fully thought out idea. We know the anatomy pretty well of the human spine. Are the ligaments in the spine correctly oriented to provide tension to hold the vertebra apart? I saw the diagrams in the article listed above, but I would like to see more visuals than the drawing of lines on pictures of the spine.

    Also, what predictions do you make using tensegrity. For example, using Newtonian physices we can make an estimate of the force applied to a bone that will cause it to break. We can predict that feet with a medially deviated STJ axis are more likely to have posterior tibial dysfunction. One benefit of a model of anatomy is that we can make predictions from it.

    Regards,

    Eric
     
  13. kevin miller

    kevin miller Active Member

    Hi Kevin K. I wondered if you were following this. I wrote to Dr. levin to make sure I was on the same page as him after my last post. He said thatwhat I wrote was exactly how he would have described it. Aparently I was not clear enough. I have thought about it some more and would like another shot.......

    In a strict Newtonian action-reaction model, neither mass deforms, transfers energy somewhere else over time or transforms the energy put into the system into another form. ALL three of these things happen in viscoelatic material and can be measured. On compression bone flexes and produces a peizoelectric pulse. Tension on a tendon produces hysteresis. In both cases energy put into the system is transfered and transformed as the tissue deforms. This is not part of the Newtonian action-reaction equation Lastly, since time is a factor in viscoelastic creep, it must be factored into any equation. There is no time function in the Newtonian equation. As for ligaments and foam... go here: http://cat.inist.fr/?aModele=afficheN&cpsidt=15427097 The celluar structure of ligaments models like a foam...follows young's modulus..... a curved line graph as tension is applied, not a straight line as we would see in an action-reaction graph. If you google ligament modeled as a foam you will get several different explainations of how this is done.

    Regards,
    Kevin M
     
  14. This is news to me. Please show me any reference that states "strict Newtonian action-reaction model, neither mass deforms, transfers energy somewhere else over time or transforms the energy put into the system into another form". Newtonian mechanics includes dynamics. Remember, Sir Isaac Newton is the inventor of the calculus (along with Leibniz), which is the method we still use to measure dynamics mathematically.

    Poor Isaac Newton. Again being told that he did not factor in time to his mathematical equations. Here is a man that invented the calculus by his mid 20's that is now used to mathematically study the dynamics of many mechanical processes, here is a man that first predicted the elliptical orbit of planets using mathematics and the concept of "gravity" and here is a man that first derived his second law of motion using the concept of change in velocity over time to explain how force, mass and acceleration are interrelated. Please don't tell me Isaac Newton did not factor time into his equations. Poor Sir Isaac is rolling around in his grave in Westminster Abbey as we speak.:bang:
     
  15. Nonsense, it may be worth going back to a basic physics text and understanding Newtonian mechanics before making comments like the one above.
     
  16. David Smith

    David Smith Well-Known Member

    Kevin M

    [​IMG]

    Kevin

    The above diagrams (from left to right ) show a graph of non linear displacement in terms of input force v's displacement in mm. Then in terms of output force v's time and finaly input force v's output force. It is impossible for the force v's force curve to be anything but straight line (and at 45dgs if the graph is drawn symmetricaly ) ie action = reaction. The displacement characteristics are a red herring in the force reaction equation.
    If you look at the spring and dashpot model you can see that the dashpot will have a time dependent diplacement. IE the faster you try to diplace the fluid from the dashpot the higher the force required or the longer a constant force is applied the grear=ter the displacement. The spring, within its limit of proportionality, has a non time dependent linear displacement. IE its displacement is relative to force regardless of the time duration of the force. In combination this can give a displacement characteristic as shown, however the input output forces are always equal. This is regardless of heat disipation, frictional forces or piezo electrical generation.

    all the best Dave
     
  17. kevin miller

    kevin miller Active Member

    Dave, Yes th input forces are equal, but what I think Dr Levin is pointing out is that the reaction is not equal in the case of viscoelastic materials because some of the force is transfered elswhere or dissipated as heat or electricity. As for Newton rolling around in his grave....time wasn't considered until relativity theory was it? Did Newton roll when Einstien published?
    Dave, can you, with the equations above, add in dissipation of some of the force input, in a non-linearway, over time? If so, I would agree with the equation.

    Kev
     
  18. Add in frictional elements. See example below. By varying the coefficients you can model any visco-elastic material with the spring, dashpot and frictional elements.
     

    Attached Files:

    Last edited: Jun 17, 2008
  19. kevin miller

    kevin miller Active Member

    That might work Simon. Give me a couple of days to work on it.

    Kevin M.
     
  20. kevin miller

    kevin miller Active Member

    Simon,

    I looked at this again and have a question. Am I reading this wrong or do the pots, springs, etc all have a straight line stress/strain curve? If this is so, we are still ony looking at an approximation. If we could put an infinate number of pots and springs, take the limit as X goes to zero..... we would get a curve. Viscoelastic materials have an exponetial stress/strain curve. Any model that does not include this will always be an approximation, an often a pretty poor one. Steve made a good point when I ran this past him. He said, what if one of these "parts" had an error that caused a "butterfly effect" in real life? If the possibility is not modeled, the model and truth will be miles apart.

    It looks like you guys are arguing that Newtonian mechanics can model or predict the natural world. You guys already know this isn't true. You can't use newtonian math to graph the structure of clouds, mountains, trees, etc. It can be done with fractals and chaos theory. I think that Steve is saying something similar.... living tissues, viscoelastic tissue, do not model well with newtonian mechanics. I appreciate that you guys are saying that it IS only a model and not meant to describe real life, but how can you say it is even an accurate model when you leave out something as vital as the stress/strain of biological materials? When you leave that out you discout or ignore energy tranformed into heat loss, energy transformed into electricity, energy dissipated at joints, the 6 degrees of freedom at every joint, the stress and reflex action of a muscle under rapid strain.... I could go on. How much error do you think ignoring these thing introduces into the equation? I am guess you think not very much, but think it over. That is an awful lot of error....that can snowball in a hurry.

    Kevin M
     
  21. Look again at the frictional element graph- he not straight line. Also think about non-linear spring elements & look again at the diagram. Moreover- look again at the diagram (hint- as a whole)
     
    Last edited: Jun 17, 2008
  22. kevin miller

    kevin miller Active Member

    Simon, That still won't work. Please google Non-Newtonian mechanics, viscoelastic materials. You will find a multitude of articles that refer to non-newtonian material. They do exist and the are viscoelastic. Biological tissue - including blood - are viscoelastic. The simply cannot be modeled acurately with a newtonian model.

    Kevin M
     
  23. And there are many many reliable sources that say they can. So who is right Kevin, you or me and my posse? You've got to be better than you are pretending to be. Please DEMONSTRATE why the above model is flawed. So that I can be sure we are both on the same wave length, please put into words the mechanics of the rheoligical model that I posted previously.
     
    Last edited: Jun 17, 2008
  24. steve1

    steve1 Member

    Apology accepted. Now let's get on with the science.


    To Quote U of Cambridge/ TLP Library/Elasticity in Biologic materials
    Summary

    “In this TLP the elastic properties of biological materials were studied. You will have learnt that few biological materials exhibit Hookean behaviour either because they do not have linear stress-strain curves, or because they do not have reversible stress-strain curves.” (Italics mine). That is what I meant when I said there was not an equal and opposite reaction. The energy goes someplace, but it is not classic elastic behavior.
    [/I]
    It gives false results. Much of biologic activity takes place in the flat part of the nonlinear s/s curve., which is more like a fluid response (hence the term 'visco elasitc'). The Elastic part of the curve Behaves like a rigid body. To quote Panjabi and White, Biomechanics of the Musculosystem, “ --cortical bone, like other biologic materials, is viscoelastic.” Fluids that behave nonlinearly, that have variable viscosity, are termed “non-newtonian” and I think it is fair to term nonlinear, viscoelastic materials such as foams as non-newtonian.



    Biologic systems are open systems that has to have continuous imput of energy, they must be fed or they dissipate, like the beer foam in your glass. Linear systems usually don't dissipate unless you add energy (rust). See wikipedia for definition of “feedbacks”.




    Aerodynamic calculations have been that it is not feasible for bumble bees to fly anymore than a pig could fly, given wings. I can't give you the specific reference. See above. What Peter is saying is that standard Newtonian concepts for elastic solids do not apply to biologic structures and we have to move beyond them. There is new math and information, (chaos theory, fractals) that may be more appropriate for biologic calculations.




    Hanging from what? The string is attached to something that gets its support from the ground. Hanging from a string, the whole structure is a pendulum and the balance is the weight at the end of the pendulum. At the point where the string attaches to the rod, the fulcrum is really the ground passing through the string. At the shoulder, the arm hanging limply by the side may be thought of as a pendulum, but once you attempt to raise the arm towards the horizontal- forgetaboutit - it is a lever and needs a fulcrum if you model the body in standard models.





    Hey - buy my DVD or invite me to talk. The DVD (about 1 hour) are like notes for my lectures (about 3 hours).




    Argue this one with Bucky Fuller. You are still talking about relative tension, the weight of the wheel, etc. The thin spokes cannot hold up the weight of the bike + rider and the load is distributed to the rim by tension.




    As you stated, the two ends try to approximate, but gravity is holding the calcaneus to the floor. The knee, precariously balanced on a frictionless joint, will flex and collapse before the heel could be lifted off the ground, unless it is held by skyhooks or biotensegrity.



    I am not sure what you mean by “reflexive”. Information transfer in the body is much more than neurologic. Much of it is mechanical - lots of references for this Including a conference at the National Science Foundation (NSF) 2002 or 3, another in Paris 2000.





    It could also be that the wrong model is being used as a basis for the calculations.

    I am saying that we should do the calculations using a different model and see if it comes out better. At this point, the calculations have not been done using tensegrity. What can be said, is that the problem of bumble bee and dinosaurs have been looked at by so called experts, and they cannot resolve the problem with standard Newtonian lever mechanics. It is time to rethink the underlying paradigm to see if there may be a more suitable model. I am proposing that biotensegrity should be tested. Do you have ant suggestions or are you still stuck in the 1600's with Borelli's model.


    I define tensegrity as does Snelson, the originator of the concept. Check his website. others are looser and, in my mind, fast and loose. I am a strict Snelsonian. I think that B. Fuller sometimes goes astray and Some points are missed by Ingber, although much of what he says is Nobel Prize stuff. That the spine is a tensegrity mast can be shown by analogy but it is difficult to test in vivo. However, it would be easy to test in the knee and the talo-tibial joint.
    Do an arthroscopic exam of the talo-tibial joint and then load it by pushing down on the femur and up on the foot. Make sure your petcocks are open so there is no hydrostatic pressure. Put a feeler gauge in the joint and slide it around. If a space exists, how do you explain it? (If any of you do this experiment - I should get full credit for the concept and be a co-author of the paper!!)

    Biotensegrity anatomy has do be thought of differently than regional anatomy, one cannot continue to think in a reductionist mode when you are working in fractals and chaos theory. There are no limb/axial skeleton boundries. If you want to see it as a thought out idea, you have to sit through 3 hours of my lectures.

    I can predict that: there is no compression load across joints, that the body is stable
    with frictionless joints, that the wrist is stable with frictionless joints, that humans can stand upright with little or no EMG evidence of muscle contraction, that the heart will empty and systolic pressure will be higher than diastolic pressure, that the bladder, bowel and what have you will empty (a consequence of non-newtonian pumps that are characteristic of tensegrity structures) and so many other things that we take for granted but could not be predicted if we looked at a biologic body through fresh, not preconceived, eyes, and tried to model them with Newtonian mechanics and Borellian concepts. We now take known phenomenon and try and explain them with Borelli (Google him if you don't know about him) concepts, But we could predict hardly any of the finding of biologic structures and physiology from Borelli. His concepts are all related to linear elastic structures and no nonlinear viscoelastic constructs are considered.

    I leave you with a quote from Poincare,
    ”It is human nature to explore everything but one's preconceptions“

    I am not sure that I have used this forum format correctly. If not - HELP!

    Thank you for allowing me to butt in on the Podiatry Arena. I am but a poor, old, orthopedic surgeon searching for some answers and, sometimes, answering other peoples questions helps clarify my own thoughts.

    Steve Levin
     
  25. kevin miller

    kevin miller Active Member

    Simon, See Steve's post. I do not know how to copy an equation or image and past it on a post like you are doing, but if you google what I suggested in my last post, you can find equations that are similar to what you would need to model biological tissue on one of the non-newtonian sites. Sorry for being a bit inadequate.

    Kevin
     
  26. I've read Steve's post and it does not address what I've just requested of you. After all, you did recently proclaim yourself to be an expert on all of this- so why defer to Steve all of the time? I'll go straight to the point then, do you understand the diagram? If so please articulate what happens when you "pull on one end", work through from beginning to end and tell me, in words, what is happening. If we ran this :material: through a materials testing machine such as an Instrom, what shape stress/ strain curve would you get?

    The problem is Kevin, while I'm trying to discuss this in an academic way with you, I'm not convinced as yet that you understand the detail of what you think you are arguing. Please prove me wrong.

    BTW you can manage attachments when you upload a new post- scroll down to where it says "manage attachments"- various file types are accepted.
     
  27. kevin miller

    kevin miller Active Member

    Simon.... Snelson, Ingber and Steve are the REAL experts. I am a pseudo-expert :) I was trying to stay on the fringes of this since this is the first time Steve has really participated here. As for the material stress until it strains..... biological materials stress in a low exponential curve, and when they strain they do not rebound to the initial position. I would like to attach a graph demonstrating this...or actually a poer point slide, b ut I do not see "manage attachments" anywhere. I am looking on the "qucik reply" page. Is this wrong?

    Kevin M
     
  28. kevin miller

    kevin miller Active Member

  29. Mart

    Mart Well-Known Member

    Hi Steve

    Firstly . . . .. great that you have taken the trouble to involve yourself in this debate . . . I cannot imagine that anyone who has been following this thread would not agree.

    Kev mentioned your anecdote a while ago. Puerile as it might sound, the only explanation I could think of at that point other than true tensegrity was that at the instant in time when a feeler gauge would be inserted into the joint space the compression support was being applied to joint margins allowing the space, I am not sure this is even anatomically possible.

    I find what you say hard to believe but if what you say can demonstrated to be true then can anyone else see any explanation for this observation other than true tensegrity?

    One of the thoughts I have had which makes me doubt true tensegrity in the foot is that te morphological features of the tarsal bones from a functional point of view seem to have evolved in response to demands of compression stresses, they are relatively broad and flat vs thin curve tubular structures as are the metatarsals? I would be interested in your thoughts on this.

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
    Last edited: Jun 18, 2008
  30. David Smith

    David Smith Well-Known Member

    Dr Steve L

    You wrote
    Most materials do exhibit hysterisis, which is what you are describing here, and yes biological tissue does exhibit significant hysterisis if it is not prestressed.
    Hysterisis is not a usual reference for interpreting Newtons law of equal and opposite reaction. Nothing returns the same energy out put as was input if it did there would be perpetual motion. EG a bouncing ball could bounce forever or a pendulum could swing forever but for hysterisis.

    Can it be assumed from this that you have not done this experiment? If so then this statement is just speculative and inconsequential. Others have done simmilar experiments with Fuji pressure film (which is as thin as a feeler gauge 0.025" - 0.040") and measured the increase in pressure between joint upon loading. There definentely was significant and expected increased pressure which should imply touching surface.

    Besides this statement, that implies a definition of non touching and therefore discontinuos compression struts, others in the biotensegrity camp have suggested that the cartilage does bear weight but itself is a biotensegritous structure of hydrostatic ballons that continue the theme of compressive structures within tension bands. so many definitions, it is difficult to have a sensible argument if the conventions of a proposed system change with the proposer.

    How is it that a common -ish injury when landing on an extended leg from a significant height is a shear fracture of the tibial condyle? (such as happened to a freind of mine when pushed into the shallow end of a swimming pool and in an effort to stop her hair getting wet she deliberately landed with straight legs)

    Kevin K

    your reference - http://www.uweb.engr.washington.edu/...roperties.html

    This is a normal explanation of the assumptions and considerations one should make when testing biological tissues. They are non linear and should be tested in a way that reasonably characterises their material properties. I don't understand your point here.

    Wood is an anisotropic, biological non linear material that has been used in construction for thousands of years. Its material properties are well known and recorded they are repeatable and predictable and structures that are constructed of wood are very successful and built using Newtonian principles.
    Other examples bilogical materials that are sucessfully used in construction and engineering and have predictable behaviours are leather, jute, cotton, intestine, hemp, bone, hair etc etc. Natural fibre rope is an example of note that has be tried tested and has very predictable properties all calculated using Newtonian principles. Non linear does not equal non Newtonian. newtonian principles are useful in predicting material properties of biological material.

    all the best Dave
     
  31. steve1

    steve1 Member

    Martin,
    If you are using Borellian mechanics: At many points during their function, the joints of the mid and forefoot foot are near vertical. These joints are essentially frictionless and the loads on them would have to be calculated as loads on a frictionless inclined plane (FIP). The acceleration of a body on a FIP depends on the sine of the angle of inclination and, as the angle approaches vertical, the sine approaches 1.0 and the mass would be in free fall. Put another way, the joint reaction force would be a function of the cosine of the angle of inclination and, as the angle approached vertical the cosine approaches 0.0 and there would be little or no compression on the joints. In frictionless joints, (slippery slopes), only forces normal (90 degrees) to the joints can transmit direct loads. Also, I doubt if the soft, cancellous bones of the foot could possibly take the compressive loads of body wt and acceleration forces That are calculated in Borellian mechanics. If they did, they should be as hard and as dense as mid shaft femur (Wolfe's law).


    Steve
     
  32. steve1

    steve1 Member

    Thaat quote was from Cambridge U. Press via Wikipedia. Argue with them.



    Yes, I have done the experiment, but with no formal and controlled protocol that would make it publishable. Most of my evaluation of joint spaces were in the knee, but I have looked at shoulders and tibio-talor joints with the same impression, there is a space that wont go away. Fugi film is notoriously unreliable and I know of no studies done in vivo. Can you site any so I can evaluate them? This is a challenge to those who can to see for yourself. Hey, I am putting myself on the line!

    Biotensegrity is still a young science and even we experts are not yet in full agreement. As I noted in my initial posting, Ingber and I do not always agree on details, but we do agree on principles. The details will be worked out by the experimenters. I am giving you my experience, which is certainly not the last word. Do all the Borellians agree on all details?


    Why does the condyle shear and not crush? Why, when the os calsis is crushed when landing on ones heel, the next most common bone to crush in the fall is L3 or L2 and not the equally soft metaphysis of the femur, tibia, pelvis, L5,L4? There are a lot of unanswered questions, most of them unanswerable using Borelli mechanics. Articular cartilage is soft and friable, easily scratched with a fingernail, and totally incapable of withstanding shear and the calculated loads of conventional mechanics.

    Steve
     
    Last edited: Jun 19, 2008
  33. efuller

    efuller MVP

    You are describing energy return not equal and opposite forces. Newton's third law still applies to biologic structures.

    Energy is egual to force x distance. As I push on a bone, it will bend. The force applied to the bone will move it a distance. While I push on the bone the bone pushes back on me with an equal and opposite force.

    When the bone is bent there is stored elastic energy in the bone. If, I were to let go of the bone and lean a small piece of wood against it, the bone would push on the piece of wood. It would not push as hard as I did to bend the bone. There is a loss of energy into friction within the bone. If you flex it enough you will see an increase in heat.



    Now, you are describing physiology, not mechanics.

    Yes, muscles need chemical energy to produce force. We don't have to know how the force was produced to mechanically analyze it. Depending on the question that is asked we can separate the physiologic from the mechanic.

    The point of the story about the lizard that can run on water was that if your calculations that say a bumblee be can't fly, and the bumblebee flies, is that your calculations or assumptions are wrong.

    So, I'm supposed to abandon Newtonian mechanics, which has worked for 100's of years and given me good answers for my questions, for a paradigm that is not yet fully thought out? I'm still questioning your problems with Newtonian mechanics. Energy is not force. Why can't you model bone as a rigid lever?

    Regarding the hanging balance. I looked up the definition of fulcrum
    Fulcrum: the support about which a lever turns
    It appears that a fulcrum does not have to be rigid and could be a string attachment.

    Fulcrum is just a name we give to a source of force. Naming a particular force as a fulcrum is not necessary to perform the analysis. If you have a muscle that pulls in one direction and another muscle that pulls in an opposite direction and those pulls are not directly in line you will get a rotation. This mechanical analysis applies to the shoulder joint regardless of whether or not there is a bony fulcrum.



    Regarding all muscles pulling down. So you agree that distal end of the gastroc muscle pulls upward. Would you also agree that it is possible to lift the calcaneus off of the floor with upward pull in the Achilles tendon while using the foot as a lever?

    To add to your last sentence ... or other muscles produced forces that cause the body to balance in such a way that the contraction would cause the body to rise upward with contraction of muscles attached to the Achilles tendon.



    How accurate does a model have to be to give you a useful answer. If I see someone who is standing and they rise up on to the ball of their foot, and I want to calculate the tension in their Achilles tendon I can get a pretty good answer.

    I can get the answers that I want now with Newtonian mechanics. I can decide whether I should put a varus or valgus wedge under the heel of my patients to treat a certain condition using Newtonian mechanics. I don't have any answers yet from tensegrity. I know how to make predictions with Newtonian mechanics. I don't even see how using tensegrity will help me make predictions.


    I saw that you claim that pressure sensative film is notoriously inaccurate. Are you saying that they show pressure when there is no pressure? Do they read too low? If there is any pressure at all then it would not be discontinuous compression.

    How do fractals and chaos change anatomy?

    All of the predictions you have made above can be made with Newtonian mechanics except for the pressureless joints. There is evidence contrary to the notion that joints don't sustain compression loads.

    Steve,
    I'm all for exploring new ideas if I see merit in them. However, you still have a long way to go to show me that Newtonian mechanics does not work for biological structures. You also have even further to go to show me that tensegrity is better than what we have. How does the heart function as tensegrity structure. What are the compression elements in the heart?

    Regards,

    Eric
     
  34. steve1

    steve1 Member

     
  35. David Smith

    David Smith Well-Known Member

    Dr Steven L


    Ditto

    As Karl popper points out if you if you do not accept that our conventions apply to your system then we cannot use our conventions to prove your system wrong.
    This is a problem of all human systems they are tautological and yet all have entropy that can be exposed and make us anxious.

    Convenient

    I am sure that you are a man of integrity and truely belive in your system unfortunately you have yet to give us ( the non belivers) any solid peg to hang our hats on. For sanity we require one peg for one hat not many pegs that causes us to choose to hang one of our many hats, that is far to bewildering for the traditional scientist but can be convenient for the metaphysicist.

    As Eric has pointed out merely showing that in some places our calculations were wrong does not prove you are right nor does it prove our conventions are wrong only that we may have used them incorrectly fot that example.

    French etymologist August Magnan wrote in the introduction of his book Le Vol Des Insects published in 1934 that it was aerodynamically impossible for a honey bee to fly.

    The incident passed into urban legend and is commonly used by creationists to point out the deficiencies of science in explaining the natural world.

    Clearly a bee can fly that is a fact.

    Scientists at Cal Tech USA have now shown how they fly both in terms of physiology and by mathematical, computer and hard modeling.

    Also from Cornell Uni

    "A computer simulation of rapidly oscillating wings and the complex motions of fluids has proved that insect flight conforms to the physical principles of aerodynamics."

    "The computer-modeling accomplishment - which is expected to aid the future design of tiny insect-like flying machines and should dispel the longstanding myth that “bumblebees cannot fly, according to conventional aerodynamics” - was announced by Cornell University physicist Z. Jane Wang.


    Karl Popper I believe was an agnostic in that he did not believe in ultimate knowledge and more, he believed that if it were possible to have ultimate knowledge then civilisation as we know it would stagnate decay and die forever.
    Whereas, with tautological systems having unavoidable entropy, knowledge and therefore human existance is assured a continual cycle of advancement though decay and rebirth of systems and their axioms.

    So like ying and yang, creator and destroyer our knowledge cannot exist without the conflict. Therefore we are useful and indisposable to each other.

    ( But for now 'we are right')

    All the best Dave Smith
     
  36. steve1

    steve1 Member

    I have made the offer of the one peg, now someone has to help us out.


    Thanks for both the history and clarification. I'll have to use other examples, and there are many.

    After 300+ years of stagnation, the time has come to search for other paradigms in tune with the times. I appreciate your recognition that the time will come that your paradigms will have to be rejected. I am aware that in another 300 years biotensegrity will have to undergo a crisis. To quote a professor from my university, Morris Raphael Cohen, From his work, Reason and Nature:
    “To be sure, the vast majority of people who are untrained can accept the results of science only on authority. But there is obviously an important difference between an establishment that is open and invites every one to come, study its methods, and suggest improvement, and one that regards the questioning of credentials as due to wickedness of heart, such as Cardinal Newman attributed to those who questioned the infallibility of the Bible... Rational science treats its credit notes as always redeemable on demand, while non-rational authoritarianism regards the demand for the redemption of its paper as a disloyal lack of faith.“

    ”Steve
     
    Last edited: Jun 19, 2008
  37. David Smith

    David Smith Well-Known Member

    Dr Steve L

    The philosophy of knowledge is a fascinating subject and my recent interest in epistimology has really opened my eyes to the paradoxes of what appears to be logical thinking. Curiously enough it confirms by long held belief that people must use systems to order their lives and understand the nature of being but the system used is immaterial. Non are right or wrong just popular or unpopular all that is required are conventions to support the theory and there is a useable system. The human mind creates both and by doing so enables our knowledge to grow.

    We imaging concepts, devise theories and invent concepts or axioms to support them. If we never did this would we 'know everything there is to know' since we would never have created anything to know.

    Thomas Hobbes wrote "The True Doctorine of The Lawes of Nature is the True Morall philosophie”, (Laviathan 1651)

    However Karl Popper wrote
    "Nature has no natural laws of its own, we as humans impose laws upon nature" (Logic of scientic discovery 1934)

    Ignorance is bliss eh! :drinks You can blame Adam and his penchant for fruit.:rolleyes:

    All the best Dave
     
  38. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
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    An Adaptive Bioinspired Foot Mechanism Based on Tensegrity Structures.
    Sun J et al
    Soft Robot. 2019 Aug 16.
     
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