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Head-bobbing of walking birds.

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Sicknote, Jul 25, 2011.

  1. Sicknote

    Sicknote Active Member

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    Does anybody happen to know why birds such as pigeons walk with bobbing heads?.

    It looks like a bit of an uncontrollable, hard wired reflex to me. Or maybe the thigh muscles and the neck muscles are both attached to the floating breastbone and it's simple physics? As one muscle pulls the other muscle has to give?.

    Or are they intentionally decompressing there spines?.
  2. Tkemp

    Tkemp Active Member

    Never thought of this before! Have been too busy protecting my lunch from them!
    Thanks to the oracle of all knowledge - Google (all bow heads in solemn reverence of its wonder) I now think its something to do with eyesight, depth perception and image stability.
    This was one of the better links I found... though you could try Wiki :D
  3. Dananberg

    Dananberg Active Member

    It is related to the number of curves (lordotic and kyphotic) in the spine of birds. Birds have two but humans have 3 of these, with the cervical lordosis decoupling the head from the movements required to store and return energy via the spine during gait (spinal engine).

    You can find details in Greckovetski's text "The Spinal Engine" published I believe in 1986.

  4. Howard,
    I hope you are well. How does a spinal curvature decouple the head or any other segment? If it is the curvature per se within the cervical spine which decouples the head, then by this mechanism the lower limbs must be decoupled from the spine via the lumbar curvature etc. Why shouldn't the thoracic and lumbar curvatures have the same decoupling effect? Or, do they...

  5. Dananberg

    Dananberg Active Member


    Greckovetsky describes a system where the verterbral facet joints act as a gearing system, providing for a mechanically efficient method by which energy can be stored and returned. As movement of the spine occurs during gait, the lumbar lordosis and thoracic kyphotic curves act to reverse motions to each other as each moves in relation to the pendular activity of the arms and legs. (Shoulder and pelvic girdles counter rotate to each other.) The cervical spine serves at the final reverse motion, so the head can be steady as the body moves beneath it. The explanation in Greckovetski's text is much clearer than I am making it, and provides the mathematic details involved in his calculations of efficiency.

  6. I'll have to pull out his text, haven't looked at it for years. Sounds a bit of a leap of faith to me.
  7. Dananberg

    Dananberg Active Member


    Having heard Grecovetski lecture on many occasions, and while you may feel like you need a "leap of faith" to understand this, I would suggest it is more of a "gap in knowledge". Review his text, particularly in regards to the uncoupling of the head from the trunk....it is a rather fascinating point of view.

  8. duplicate
  9. Howard, it probably is a gap in knowledge. By leap of faith, I meant that while I find Gracovetski's theories interesting, I don't see much in the way of evidence to support them. Are there any studies which have tested the direction of power-flow and/or coupling between say, the lumbar spine and the hip? Only yesterday I was talking with Bri Rothbart regarding the only moderate coupling between the hip and the rearfoot. What does the literature tell us regarding the coupling between the vertebrae and the hip? Indeed, if the spine is driving the lower limb during gait (which if I recall is the central premise of spinal engine theory), then the power-flow should be in a proximal to distal direction from the spine to the pelvis, to the femur, down the shank and to the foot- agreed? What does the literature tell us here?
  10. Dananberg

    Dananberg Active Member


    The power from the spinal engine is directed TO THE SWING LIMB, and not to the weight bearing limb! As the pelvis returns the energy stored by opposing arm and leg swing, it will rotate in the same direction as the limb entering pre-swing phase. It is the combination of spinal engine power, combined with the potential energy stored within the limb during extension, which then creates as energy return generated swing phase. Iliopsoas only needs a quick impulse to PERPETUATE swing phase motion. All a rather elegant orchestration designed to minimize energy necessary from ambulation.

  11. Ok can see where this going, but here we go again. So, power flow to the swing limb is proximal to distal- right? And the calf muscles fire during propulsion just for a laugh? Old stump, bored already.

    " and if the night runs over,
    And if the days won't last...
    It's just a moment...
    This too shall pass. "

    Stuck in a moment- u2
  12. Dananberg

    Dananberg Active Member


    You are correct in the proximal to distal spinal engine to limb linkage. The calf fires concentrically just as double support phase begins, thrusting the limb into swing phase from below as the spinal engine drives it from above. My general arguement has always been that when the knee and hip flexing at this moment, calf firing would be extremely inefficient to drive the CoM. However, it is ideally situated to propel the limb into swing phase, which subsequently acts on the CoM.

    Prehaps if you step out of your own STJ centered viewpoint for a bit, you may see the elegance in all of this, as it provides for a highly efficient, energy saving gait system.

    I never get board trying to piece together the magnificance of how components all work together. Sorry you don't feel this same reverence for human design.

  13. Yeah, STJ centric, that's me:rolleyes:. Remind me again how the erector spinae drive the swing limb forward? Remind me again about that research evidence demonstrating the coupling and power flow direction between the hip and the spine through gait. Remind me again of any, yes any research evidence which supports the spinal engine theory- seriously, any?

    I'm interested in human design, it's not the be all and end all of my life though. I have a family, hobbies and a job. I do get bored of discussing the same old topic over and over and over. I am a scientist by training though and will never, ever believe someone just on their say so. "The moons a balloon", sh!t, really? I love a good theory and love them even more when there is some good research evidence to back them up. I really do love it when blind-hypotheses are put forward by people who have a vested interest in a product which they have trademarked, copyrighted, patented etc. Like: "kinetic wedges change foot pressures" or, "kinetic wedges change posture". Yet, when such statements are subsequently tested independently and they are disproved and shown to be false (http://www.asbweb.org/conferences/2003/pdfs/163.pdf http://www.health.uottawa.ca/biomech/lab/docs/isb19_kr.pdf ) I love it to bits. Love a bit of science, me. And having the "gaps in my knowledge" filled in. And you Howard? You appear content and happy in your comfort zone Howard and I can respect that too. I did try to talk with you about the implications of the bipedal spring mass model theory of human walking a while ago, but you didn't appear overly interested in the "magnificance" of how components work together then. Perhaps if you'd have stepped out of your own big-toe joint centred viewpoint (that is the equivalent of the ridiculous statement you just made regarding my view of ambulatory biomechanics, BTW) at that time, you may have seen the elegance in all of that, as it provides a highly efficient, energy saving gait system. Perhaps it was you that was "board" then, or even: bored. Never mind.

    Here's how it works:
    You say: the spinal engine drives the swing leg forward to achieve forward motion during gait
    I say: Really? Show me the proof?

    You provide the proof.

    We call that "academic debate"

    To quote my friend Robert:
    "1: Extraordinary claims require extraordinary proof. If it does what it says, you should have no problem with this.

    2: What proof will you accept that you are wrong? You ask us to change our mind, but we cannot change yours?

    3: It is not our responsibility to disprove your claims, but rather your responsibility to prove them.

    4: What part of "meow" don't you understand?!"

    P.S. If I want to walk backwards, what happens then?
  14. Dananberg

    Dananberg Active Member


    To answer the "PS" question first, you STEP backwards. Also true when you move to the left or right....you step in the direction of motion, destabilize the CoM and as gravity exerts its force on the CoM, it uses the mechanical advantage provided by the length of the limb as a lever to drive the ground in the opposite direction. This is what makes this concept so appealing; its simplicity and omnidirectional application. In the thousands of patients I have treated over my practice life, I have never seen anyone (who could actually walk) not step in the direction of motion as the first part of the walking process. Couple that with Herman's findings that swing phase is instinctive in humans (Neural Control of Locomotion, 1976). Infants already have the kick phase reflex and long before they can walk or stand. Not sure what else to say.

    Now, onto the more insolent aspects to your last post. To be clear, I never asked for or needed you to prove or disprove what I have said. That is your fantasy and one which you engage in repeatedly on PA with those with whom you disagree. Over my career, I have published a wide variety of reseach studies on topics ranging from changes in ankle ROM when manipulative techniques are applied (Dananberg, HJ, Shearstone, J, Guiliano, M “Manipulation Method for the Treatment of Ankle Equinus, “ Journal of the American Podiatric Medical Association, 90:8 September, 2000 pp 385-389), to changes in hip joint ROM when changes to foot orthotics are made (Dananberg, HJ, “Gait Style and Its Relevance in the Management of Chronic Lower Back Pain”, In Proceedings, 4th Interdisciplinary World Congress of Low Back & Pelvic Pain”, Ed, Vleeming, A, Mooney. V, Gracovetsky, S, Lee, D, etal, November 8-10, 2001, pp 225-230). I have also published outcomes in chronic back pain subjects when CFO's are utliized (Dananberg, HJ, Guiliano, M, “Chronic Lower Back Pain And It Response to Custom Foot Orthoses”, Journal of the American Podiatric Medical Association, 89:3 March, 1999 pp109-117). I never expected anyone to believe what I said....I wanted to provide as much proof as I could, or at least provide evidence for others to build on. There is considerable published data by others which fully supports my position, yet, in academic debate, there will always be differences of opinion. It is the difference which creates knowledge growth.

    As far as future reply comments, try civility for a change, Simon. Your current approach is not becoming of someone with your expertise and credentials.

  15. Sicknote

    Sicknote Active Member

    Animals effectively lengthen their limbs by making their spines extremely flexible (decompression). Essentially, the flexion and extension of the spine allows the limbs to swing more, increasing stride length & efficiency. This can also apply to humans with flexible spines.

    Spinal decompression.

  16. Yeah, the last time I looked the majority of humans had gotten up off all fours (some are still dragging their knuckles though).
  17. David Wedemeyer

    David Wedemeyer Well-Known Member

    Howard where can I obtain the papers referenced above?

    Thank you
  18. Sicknote

    Sicknote Active Member

    You don't have to get on all fours.

    Humans have the ability to decompress there spines too.

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