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Biomechanics and Physics

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kate Wabel, Jul 24, 2006.

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  1. Kate Wabel

    Kate Wabel Banned

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    Biomechanics is not physics Simon!

    <ADMIN NOTE>: This topic has been split off from the New goals for Podiatric Biomechanics as its worthy of its own discussion </>

    Would you please explain how physics is applied to self adjusting biological systems?

    Physics is: 'The sciences that treat of inanimate matter and of energy,
    apart from vitality.'
    Last edited by a moderator: Jul 26, 2006
  2. efuller

    efuller MVP

    Hi Kate,

    Gladly. I assume by self adjusting you are talking about the body at a physiological level in terms of hormones, etc. and the achievement of homeostasis. Physics can be used to describe the motions of the skeletal system. If you accept Newton's laws as valid then any motion of any living body can be described using physics. Newton's 2nd law says it all. For linear motion the acceleration of the body is equal the force applied divided by the mass. (F = ma, a F/m) For angular acceleration the net moment is equal to moment of inertia x angular acceleration. So, any time you see a body part start to rotate relative to another part, there must have been a moment applied. Living things still have to obey the laws of physics.


    Eric Fuller
  3. Atlas

    Atlas Well-Known Member

    Kate I think there is a place for physics in musculo-skeletal medicine, although I do think it is over-complicated.

    You can get a long way understanding compressive and tensile stress for instance. An acute ankle ligament sprain for example would not appreciate (at a macro or micro level) continued tensile stress.

  4. Actually, Kate, I believe that Dr. Spooner has an enhanced understanding of his discipline. He is one of the few PhDs contributing to this forum, has both taught in Podiatry Schools and contributed to the podiatric literature with original research and, as far as I'm concerned, has a better understanding of foot and lower extremity biomechanics than 99% of the podiatrists around the world. He is one of the leaders of our profession in podiatric biomechanics.

    Contrary to your opinion that Dr. Spooner uses a "blunderbuss approach", I believe that he is quite specific and selective in his criticisms of certain ideas and individuals that don't make good sense to him and that don't follow accepted laws of physics. Personally, I believe his comments add great value to this forum and I know they are enjoyed by many of the lurkers and contributors on Podiatry Arena. Please tell us your background in podiatry or in academia in general, Kate, that you have the right to judge that Dr. Spooner has "an impaired understanding of his discipline."
  5. javier

    javier Senior Member

    Excuse me if I am wrong, but do you know personally all podiatrists around the globe? Have you evaluated biophysics knowledge from all podiatrists around the globe for making this statement?

    It is second time I read this statement, and it is a unrespectful way to address peers if you can not offer any real data if it is true or not.

    I have enjoyed both Dr. Spooner and your contributions on Podiatry Jiscmail and on this forum; but lately comments are offensive not only towards some individuals, they are also towards colleagues that we have not had the opportunity to research and publish.
  6. Javier:

    99% may be an unfair estimate. It is probably more like 99.67% (OK, I'll admit it is only a guess :p) from my discussions and lectures to podiatrists in 7 countries, my lectures at podiatric biomechanics seminars in these countries for the past 21 years and my review of the last 40 years of podiatric biomechanics literature. What would your estimate of Dr. Spooner's knowledge be, Javier? How many times have you been invited to lecture out of Spain on podiatric biomechanics? And why have you not had the opportunity to research and publish? What is preventing you from doing so? I would say that I am respectful to all those that show respect to others and don't try to use this forum to promote their own self-serving ideas and don't criticize respected members of the podiatry community for purposes that have nothing to do with academic disagreements.

    However, Javier, I am sorry if I offended you. Good luck with your upcoming research and publication of that research.
  7. javier

    javier Senior Member

    There is a world of difference between guessing and evidence.

    I think it is clear that Dr. Sponner have shown an encyclopedic knowledge about the subject.

    None. I have invited to lecture about diabetic foot orthotic management. I know it is not rocket science but it helps people to keep their lower extremities for having muskuloeskeletal injuries.

    Because I have been working for years for achieving a successful practice by my own. I hope in next years I will be able to perform some research from my own pocket (no funds are available for podiatrists in Spain).

    Nonsense is not worth to be discussed, but neither criticism can be considered as personal attacks.

  8. Kate Wabel

    Kate Wabel Banned

    Mr Kirby, isn't the whole purpose of this arena for full & frank discussion in order

    to arrive at scientific accuracy, and not the academic history of contributors?
    Are we not allowed differing opinions in this forum?

    Mr Spooner seems to be of the opinion that the laws of physics may be applied to biomechanics.
    Once again I contend that anyone who doesn't accept that the science of physics applies only to inanimate matter (see the Oxford English Dictionary definition) has the most basic misunderstanding of his own scientific discipline.

    If you disagree with this definition, please tell me on what grounds.

    Physics does not enunciate mathematical laws applicable to the clinical practise of medicine, since it deals exclusively with inanimate matter & energy, excluding vitality. (please refer to the OED definition)

    I await Mr Spooner's defense of his contribution concerning physics & biomechanics.

    Kate Wabel
  9. Kate Wabel

    Kate Wabel Banned

    Ron, thank you for your reply but I must disagree, the stresses & strains of living

    tissue are biological concepts and therefore the science of physics once again is not applicable. (Oxford English Dictionary definition) Physics: "The sciences that treat of inanimate matter and of energy, apart from vitality."
  10. Kate Wabel

    Kate Wabel Banned

    Hi Eric, thank you for your reply, I was talking about the body as a whole.

    Physics can be used to describe the motions of the skeletal system only in a dead body.
    When Newton was referring to 'the body' he meant 'the inanimate body' eg: a bullet, since physics deals exclusively with inanimate matter & energy, excluding vitality.
    The study of biomechanics relates to biology not physics.

    I was pointing out to Mr Spooner, that he appears not to understand that physics is not a biological science, & therefore cannot be applied to biomechanics which certainly is a biological science.

    Kate Wabel
  11. efuller

    efuller MVP


    Why can't physics describe the motion of living bodies?

  12. Kate Wabel

    Kate Wabel Banned

    Hi Eric, the answer is in your question. Physics does not describe anything vital

    ie: living. It deals purely with non vital matter & energy.

  13. javier

    javier Senior Member

    This is because there is a discipline called Biophysics or biological physics. Just type biophysics on Google, you will find plenty of references. Also it is on the Oxford Dictionaty Online http://www.askoxford.com/concise_oed/biophysics?view=uk
  14. Biomechanics is the research and analysis of the mechanics of living organisms. Aristoteles might be considered the first biomechanicist. He wrote the first book called "De Motu Animalium" - On the Movement of Animals. He not only saw animals' bodies as mechanical systems, but pursued such questions as the physiological difference between imagining performing an action and actually doing it. The research and analysis can be carried forth on multiple levels, from the molecular, wherein molecular biomaterials such as collagen and elastin are considered, to the macroscopic level, all the way up to the tissue and organ level. Some simple applications of Newtonian Mechanics can supply correct approximations on each level, but precise details demand the use of Continuum Mechanics.

    Some simple examples of biomechanics research include the investigation of the forces that act on limbs, the aerodynamics of bird and insect flight, the hydrodynamics of swimming in fish and locomotion in general across all forms of life, from individual cells to whole organisms. The biomechanics of human beings is a core part of kinesiology.

    Applied mechanics, most notably thermodynamics and continuum mechanics and mechanical engineering disciplines such as fluid mechanics and solid mechanics, play prominent roles in the study of biomechanics. By applying the laws and concepts of physics, biomechanical mechanisms and structures can be simulated and studied.

    Biomechanics of the bones
    Bones are anisotropic but are approximately transversely isotropic. In other words, bones are stronger along one axis than across that axis, and are approximately the same strength no matter how they are rotated around that axis.

    The stress-strain relations of bones can be modeled using Hooke's Law, in which they are related by linear constants known as the Young's modulus or the elastic modulus, and the shear modulus and poission ratio, collectively known as the Lamé constants. The constitutive matrix, a fourth order tensor, depends on the isotropy of the bone.

    In physics, Hooke's law of elasticity is an approximation which states that the amount by which a material body is deformed (the strain) is linearly related to the force causing the deformation (the stress). Materials for which Hooke's law is a useful approximation are known as linear-elastic or "Hookean" materials.

    For systems that obey Hooke's law, the extension produced is proportional to the load. The most commonly encountered form of Hooke's law is probably the spring equation, which relates the force exerted by a spring to the distance it is stretched by a spring constant, k, measured in force per length.

    F= -kx


    x is the distance the spring is elongated by,
    F is the restoring force exerted by the spring, and
    k is the spring constant or force constant of the spring.
    When this holds, we say that the spring is a linear spring. The negative sign indicates that the force exerted by the spring is in direct opposition to the direction of displacement. It is called a "restoring force", as it tends to restore the system to equilibrium

    Hooke's law mathematically comes from the fact that in most solids (and in most isolated molecules) atoms are in the state of stable equilibrium.

    A.C. Ugural, S.K. Fenster, Advanced Strength and Applied Elasticity, 4th ed
    Fung, Y.C. "Biomechanics: Mechanical Properties of Living Tissue" (2nd ed.). New York: Springer.
    Humphrey, Jay D. "Cardiovascular Solid Mechanics: Cells, Tissues, and Organs." New York: Springer.
    Vogel, Steven. (2003). Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press.
    Last edited: Jul 25, 2006
  15. Kate Wabel

    Kate Wabel Banned

    Hi Javier, thank you for your reply, I imagine that Biophysics is a more recent

    concept than physics.

    Mr Spooner could be more specific with his wording.
    After all medicine is a very specific science.
  16. Kate Wabel

    Kate Wabel Banned

    Mark, thank you for yor reply, I don't recall challenging the definition of

    I was merely pointing out that Mr Spooner is no expert in physics..(his wording in responses.. not mine)
  17. An expert is someone who has succeeded in making decisions and judgements simpler through knowing what to pay attention to and what to ignore.”

    Francis Charles Publius (b/1933)
  18. javier

    javier Senior Member

    Perhaps you should contact Dr. Spooner privately. There is an option on this forum for doing it.
  19. Kate Wabel

    Kate Wabel Banned

    Javier, thank you for your reply, I have already contacted Mr Spooner privately.

    He appears to have nothing to say about his definition of physics (he didn't mention biophysics!)) when applied to biomechanics.
  20. Kate Wabel

    Kate Wabel Banned

    Mark, quite. Are you referring to Mr Spooner?

    As for your remark about the Oxford English Dictionary being 'terribly unreliable', which dictionary do you suggest to clarify the definition of physics?

    Kate Wabel
  21. achilles

    achilles Active Member

    I am really intrigued by your thoughts.
    Do you feel that the application of physics to a living organism does not stand, as we are not applying the laws of physics to a passive, non-reactive body??
  22. Kate Wabel

    Kate Wabel Banned

    Tony hi, absolutely I do! you cannot apply the law of

    physics to a living organism, as was my original observation.
    Mr Spooner, (& now it seems others) are challenging the definition of pure physics.
    Had they described biophysics I would not have entered this debate!!

    As I have stated, medicine is a specific science & as such, so called experts should surely use specific terms.

    I have no 'bug bear' with anyone, I just like people to say what they mean.
    If we do not use the English language accurately, how can we hope to be scientifically accurate?

    Kate Wabel
  23. Kate,

    Do you have something personal against Dr. Spooner? It sure seems so from reading your many postings where you are focusing only on him and what he said some days ago. Now if you have something personal against me, I can certainly understand your feeling that way since I can be absolutely nasty (especially if I haven't had at least 7 hours of beauty rest every night) and have been known to be also very opinionated at times. In fact, I can be so mean-spirited that I can get podiatrists from 6,000 miles away from my little computer to say that I am offensive (actually I was better known for my defensive skills since I was never much of a scorer in any sport). But poor Simon, he is such a lovable fellow....with never anything rude or offensive to say to anyone....how could you not just want to hug him? :p

    On a more serious note....regarding your postings in which you state that physics can not be used to describe biological systems. Kate, this is such pure utter nonsense that I will end this discussion with you by stating that you need to come out into the bright light and look at the wonders of the modern world of research biomechanics.You see, physics is the basis of what we, in the modern research and clinical world, use for the study of the mechanical properties of biological systems. Your statement:
    is ludicrous!! Really, Kate, if you made that statement to any PhD biomechanist anywhere on this planet, they would probably think you were either crazy or hopefully just a poorly informed individual that doesn't know when to keep their opinions quiet.

    Here is a good definition of biomechanics for you to start with:

    Here are some other references for you to study if the goal of yours is to become more educated on physics and biomechanics. However, if your goal in making these statements is to draw a certain individual into a public argument with you then you will likely have little success in doing so:

    Last edited: Jul 26, 2006
  24. achilles

    achilles Active Member

    Not quite sure as to whether Simon is warm and cuddly, Kevin??!! ;)

    I can empathise somewhat with Kate's point in that, and forgive me if I am wrong, the use of terminology is the concern here, not the concept of biomechanics.
    As you have said many times, Kevin, until we are using scientific terminology that is coherent across many disciplines, communication of understanding will continue to cause problems
  25. Tony:

    Biomechanics is the more commonly used term to describe the mechanical analysis of biological systems. I think that one should look at scholarly journals for the correct terminology: Journal of Biomehanics, Clinical Biomechanics, Journal of Applied Biomechanics, Applied Bionics and Biomechanics, Biomechanics and Modeling in Mechanobiology, Journal of Biomechanical Engineering.

    I believe that the term "Biophysics" is a more broad term to include multiple biological disciplines and not specifically dealing with mechanics. I have not come across the term "biophysics" when interacting with members of the international biomechanics community over the past 20+ years. From my limited understanding of the term "biophysics", it generally deals with chemical interactions at the molecular level. I believe it was called "biophysical chemistry" during my undergraduate years.
  26. Atlas

    Atlas Well-Known Member

    One should be judged on what they type/say, and how they support it. The number of degrees you have, and how high/low you are in the acedemic hierarchy should be absolutely irrelevant.
  27. Ron:

    This is only true in a perfect world, one that we don't live in. When was the last time that someone that did not have any degree and had no faculty appointment lectured at a scientific seminar that you attended?? The only person that I know that lectures at podiatric seminars that doesn't have a degree is Jeff Root, but his name speaks for itself.

    The truth of the matter is that the leaders of any profession just don't appear on the scene, they have done something significant or have done many significant things over a long period of time to be elevated to that position. They have published research, invented techniques or theories or tests, or have promoted their profession in some positive way. It doesn't happen overnight but is a long, painstaking process that very few individuals are capable of achieving within each profession. Ron, please name one individual that is respected within the academic world of the podiatric profession that does not have a degree and doesn't have a faculty appointment. I am interested in your response to this since you obviously feel that some people just come about all this knowledge and wisdom naturally, without having to work for it by attaining long hours of study and attaining academic degrees.

    Finally, Javier asked how I knew that Simon Spooner had greater knowledge in biomechanics than 99% of the podiatrists around the world. I simply stated that I believe I have a very good appreciation of what the state of biomechanics knowledge around the world is within the podiatry profession, since I have lectured in many countries, lectured to and taught thousands of podiatrists in biomechanics over the past 21 years and personally know and am friends with most of the leaders within podiatric biomechanics around the world. In fact, come to think about it more, saying that Simon Spooner is only smarter in podiatric biomechanics than 99 out of every 100 podiatrists around the world is probably an insult to him.
    Last edited: Jul 26, 2006
  28. Atlas

    Atlas Well-Known Member


    You talk about the utopia of a perfect world, and then refer to the academic world as if itself is indeed perfect. If it was perfect, then I guess, respect within it, is an understandable goal.

    That is an nth order priority for some of us. I just want to be good at my job and earn a living.

    On one hand you can't fathom anybody 'low' on the academic hierarchial tree having anything to contribute. On the other you raise Root. It epitomises what is possible, and thank goodness, for his sake that he ain't an unknown 'newcomer' here jousting verbally with respected heavyweights.

    I will answer your question this way. I graduated more than a decade ago, and as a young green graduate, rushed out to seminars to absorb all that I could from those respected persons with an alphabet after their name. All I got was virtually critical analysis of literature. This if fine, but it wasn't what I paid for. I wanted to be a better practitioner the following Monday.

    It may suprise you, but a sports trainer at a suburban football club (St.Kilda) here in Melbourne, taught me more about strapping/taping for instance than any other person or institution or seminar. Doubt he even finished school.

    I learn a bit here as well, but not only from the Kirby's, Smith's and Fuller's; but also from the Fellners, the Scorpios and others etc.

    And I would like to learn from a P&O about semi-weight-bearing casting and EVA devices.

    Common sense is not learnt at university; or does not magically arrive after a PhD. Getting patients better is at least 70% common sense.

    I agree with you though that Kate's point is a touch pedantic and quit harsh. However, Simon admitted to making fun of another poster here only last week. I am sure we are big enough to take some of our own medicine.

  29. PodAus

    PodAus Active Member


    What exists without the direct influence of energy? Nothing. Therefore, what exists without the direct influence of physics? Nothing... not a thought, not love, and certainly not foot/leg function

    Quantum mechanics and parallel philosophical thought/debate may soon require an update to your directorate in life (the Oxford Dictionary).

  30. davidh

    davidh Podiatry Arena Veteran

    Hi Kate,

    Just to agree with your observation re the word physics.
    Good one - and had it emanated from another (shall we say) more well-known direction it would probably have been applauded. As it is, an observation, coupled with what you (correctly IMO) see as another contributors attitude (not a personal attack - you want to see an attack look over some previous posts where I or Ian Linane have contributed) has merely ruffled a few feathers and caused a little fuss (never a bad thing IMO).

    So, having checked two dictionaries, I'm with you.
    You are quite correct.

  31. PodAus

    PodAus Active Member

    Ok - so according to this direction, and subsequent to this Oxford Dictionary entry, as Podiatrists, we don't even have the right to be discussing physics - we can only treat the feet


    • noun another term for CHIROPODY.

    — DERIVATIVES podiatrist noun.

    — ORIGIN from Greek pous ‘foot’ + iatros ‘physician’.


    • noun the treatment of the feet and their ailments.

    — DERIVATIVES chiropodist noun.

    — ORIGIN from Greek kheir ‘hand’ + pous ‘foot’.
  32. David Smith

    David Smith Well-Known Member


    Not sure if your original quote was passionate and intended for deeper discusion or if it was a throw away line that you now find you have to unintentionaly defend.

    I like the discussion "is biomechanics Physics" though.

    Your (OED) definition of physics "The sciences that treat of inanimate matter and of energy, apart from vitality."

    My thoughts are;

    Physics from the Greek Physis means natural things or things of nature.
    And 'ics' meaning to treat or consider. To consider natural things.

    Vitality means, in this context, to have the force of life.

    So physics is to consider all things natural but not the force of life.

    The force of life is ephemoral and beyond our ken at this time and especially in the time of the Aristotle and ancient greeks of 2500yrs ago. We are not able to control this force and breath life into the lifeless. We can only manipulate the physical to create the right conditions for life. When it occurs it is a miracle some would say and the exclusive franchise of their God.

    Physics can also be defined the study of the influence of forces on matter.
    So when using physics we can consider those things that contain life but not the life force itself because physical forces can not have direct influence on the ephemoral life force, only the physical conditions that allow life.

    Therefore it is still true to say that physics = "The sciences that treat of inanimate matter and of energy, apart from vitality."

    Mechanics is a branch of physics I think that is undeniable so therefore biomechanics becomes self explanatory IE the mechanics of the living body. It does not however propose to treat or consider the force of the life within the living body.

    Therefore I conclude biomechanics is a branch of physics

    Cheers Dave Smith
  33. Kate Wabel

    Kate Wabel Banned

    Mr Kirby, now you are telling me to keep my opinions quiet!!!

    You have also told me my definitions are LUDICROUS!!
    You then give me a definition of biomechanics!! Never challenged!!

    I still await your own definition of physics.

    Are you unable to provide one?
  34. Kate Wabel

    Kate Wabel Banned

    Hi David, thanks for your reply, here we go again disagreeing with you!!

    we cannot consider those things that contain life.
    Anything inanimate does not contain life!
  35. Kate Wabel

    Kate Wabel Banned

    Dear PodAus, you miss my point, we, that is podiatrists

    can discuss anything. Including physics.

    All I ask is that it is aplied appropriately to any discussion
    ie. not biomechanics!
  36. PodAus

    PodAus Active Member

    And that is my point - for the lack of a better term, the use of the word and traditional application of 'physics' to the obseved motion of a foot, leg or a piece of wood is perfectly valid in ANY discussion....

    now, what were we discussing??? Something about feet??:confused:
  37. Donna

    Donna Active Member

    So where does this leave the Tissue Stress Theory? If physics cannot be applied to biological/living systems... :confused:
  38. efuller

    efuller MVP

    Maybe it is improper to say physics. Maybe we should just say mechanics. We can say that living things are machines and that mechanics is the study of machines. We just happen to use Newton's laws and the physical descriptions of energy to study machines.

    Kuhn noted that a group (like podiatrists) can take a word that has a certain meaning in one setting (Oxford English Dictionary) and that word can have a different meaning within that group. Certainly within our comunity, biomechanics is physics of the foot.

    I think the tissue stress paradigm is safe for now.

  39. Kate Wabel

    Kate Wabel Banned

    Hi Donna, glad you've entered the discussion. I see from Eric's answer he's now

    calling us 'machines!'

    He's quite correct when he says 'mechanics is the study of machines'

    However: machines are "mechanical devices with moving parts, often
    powered by electricity."

    Heaven help him in a 'power cut.'

    Regards, Kate
  40. David Smith

    David Smith Well-Known Member


    You wrote

    Does this imply that machines do not have life. (of course they don't) so then you strenghten my argument since this would imply that life is more than just the energy that we can consider and measure. Therefore we cannot consider or measure the life force and this is what is meant by the OED definition.
    We cannot (it is impossible to) consider the life force.

    How would you quantify human movement without physics Kate?

    Cheers Dave
    Last edited by a moderator: Jul 28, 2006
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