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The Determinants of gait

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Apollus, Oct 26, 2010.

  1. Apollus

    Apollus Member

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    Hi all,
    Hoping you can help...I am a student at birmingham struggling with pelvic rotation and tilt :craig:
    I understand why they happen and how they help but what I havn't found the answer to is HOW they happen...
    Is it a passive motion that occurs or is there a specific muscle/group of muscles that brings them about?
  2. Re: determinants of gait

    It's the interaction between external and internal moments acting upon the body.

    Here's the seminal work:
  3. Apollus

    Apollus Member

    Re: determinants of gait

    Great cheers :)
  4. Craig Payne

    Craig Payne Moderator

    Re: determinants of gait

    FYI, from my notes:
  5. Apollus:

    Here is the text of the lecture (along with one of my drawings from the lecture) that I give on abductory twist where I discuss the need for tranverse plane pelvic rotation during gait and how this transverse plane pelvic rotation is one of the factors causing abductory twist.


    Attached Files:

  6. DanthePod

    DanthePod Member

    Hi Kevin .... Just got the chicken out of the freezer again!!!!!!! I would have thought that late phase subtalor joint pronation may be related to functional limitation at the ankle joint and it would be difficult to determine weather or not this late phase pronation is to the possible compensation that could be occuring due to functional restriction at the ankle joint?? So is the abductory twist a sign of pronatory compensation related to a sagittal plane issue as much as it is related to the compensation due to a :wacko:lack of stability of the foot in the frontal plane ? cheers Dan
  7. David Smith

    David Smith Well-Known Member


    You wrote
    Simon replied
    And that's exactly it!

    However it may be useful to identify and describe the concept of unbalanced forces & moments. In ambulation these are very often due to inertial force.

    Simply put, A moment is caused when a force acts on a lever, this causes or tends to cause a rotation about some point of interest. This is not strictly true though since without an opposing force there is just acceleration in a straight line and no angular acceleration about a point of interest.

    So if you push on a stick that is suspended in space it goes in a straight line. (ignoring moments of inertia and radius of gyration which is to much to go into here) If you fix one end with a frictionless joint the stick will rotate about that joint as you push but without any tendency to bend the stick. You now have an angular acceleration as you push the stick and it rotates.

    If you anchor one end the stick without a joint it will tend to bend as you push on the other end NB this bending can be thought of as a tendency to rotate about any point of interest along its length.

    Now remember unbalanced forces, well now you have to grasp inertial forces.

    Inertial force is the reaction of a mass to acceleration, inertial force acts in the opposite direction of acceleration. It is what makes you feel heavier (and actually weigh more even tho your mass remains constant - remember F=M*A and M*A=F) in a lift as it accelerates during the start of going up. It is what kills you when you hit the ground after falling from a great height i.e. deceleration is acceleration just the same but in the opposite direction, kind of.

    Getting back to the stick, if you put a large lump of clay (i.e. a mass) on one end of the stick and grasping the other end try to launch the clay lump over your neighbours greenhouse, then as the clay mass accelerates it will apply an inertial force in the opposite direction. This force will tend to rotate the stick, or rather it will bend the stick since it is held firmly anchored in your hand at the other end.

    So the accelerations and consequent inertial forces of walking cause moments about the pelvis in the transverse saggital and frontal plane. These inertial forces are the reaction, equal and opposite, to the ground reaction forces from the foot. Without a real force, e.g. GRF, there can be no inertial force, which is often known as a fictitious force.

    Where these inertial forces act on a lever then you have a moment about a point of interest such as a joint i.e. hip, sacro-iliac, lumbar spine. These joints allow relative rotation of the upper and lower limbs, i.e. torso and legs, and each lower limb about each other.

    Therefore the pelvis and its joints allow rotations to happen as the body or its segments accelerate. The neat bit here are muscles and ligaments, they apply forces on lever arms that produce moments in the opposite direction to those cause by inertial forces due to segment acceleration.

    So as the head & torso (HaT) accelerates forward the inertial force of the mass of the HaT acts backward and so the HaT would topple of the legs in the saggital plane if not for the muscle-ligaments forces stopping it rotating. The swing leg would cause you to rotate about your opposite hip joint and gravity would cause you to rotate about the hip joint of the supporting leg during contralateral swing.

    The latter example is one of unbalanced moments due to real forces, i.e. GRF and gravity.

    The mechanics of human walking demand that the joints rotate to allow the movement required. The muscles and ligaments mediate the forces, real and inertial to allow just the right amount of rotation.

    Of course the muscles are active in producing the acceleration forces in the first place. So the reactions to accelerations & forces caused by muscles are mediated transmitted and controlled by muscles and ligaments via joints and bones. The bones can be imagined as the sticks between the hand and the clay.

    Hope that's not to confusing to get your head around.

    Regards Dave
  8. Apollus

    Apollus Member


    -inertia i s a mass's way of resisting forces applied to it.
    -inertia caused by GRF creates moments around the pelvis, ie. causes it to rotate around whichever axis in response to inertial force.
    -ligaments resist excessive movements in joints.
    -muscles create the forces/moments which in turn gives the various body parts inertia as they resist these forces...and it is this inertia that causes the pelvis to rotate about the axes?
    -am I right in thinking that, as the swing leg is accelerating forwards it is its inertia that pulls the corresponding side of the pelvis to rotate forwards? in the horizontal plane?
  9. David Smith

    David Smith Well-Known Member

    Yep, you've summarised that quite well except for the last bit that I have highlighted in red, which is almost right but not quite.

    Remember inertial force acts in the opposite direction to acceleration.

    As the leg swings thru the inertial force acts forward when the leg decelerates (which is actually acceleration backwards) toward the end of swing. As the leg accelerates from toe off the inertial force acts posterior in direction. After mid swing the inertial force action direction changes.

    Regards Dave
  10. Apollus

    Apollus Member

    oh yeah, i see where i went wrong there.
    thanks for your help :)
  11. Dan:

    The simplest way to view late midstance subtalar joint (STJ) pronation is to go back to the basic physical cause of any STJ pronation motion. In other words, the only reason that late midstance STJ pronation can occur (i.e. an acceleration of STJ pronation) is when the STJ pronation moments are of greater magnitude than the STJ supination moments. Of course, we may not know where these forces originate from that cause these STJ moments. We do know that these forces that cause STJ moments will be a combination of both external (e.g. GRF) or internal (e.g. posterior tibial tendon tension) forces, with many possible contributing sources, both proximal and distal to the STJ.

    I agree with you that a limitation of passive ankle joint dorsiflexion at the ankle joint may contribute toward increasing the tendency of an individual displaying increased STJ pronation moments during late midstance. However, one could certainly also argue that if a lack of ankle joint dorsiflexion occurred in a foot with a laterally deviated STJ axis and high midtarsal joint/midfoot stiffness, then that same lack of ankle joint dorsiflexion could then cause an early heel off with earlier STJ supination motion during late stance phase. Therefore, I am not too impressed about "a lack of ankle joint dorsiflexion" being considered a sole cause of any injury without also considering the sagittal plane compliance of the midtarsal and midfoot joints and the spatial location of the STJ axis.

    Once the late midstance pronation occurs, then the concomitant internal rotation of the tibia will cause more elastic strain energy to be developed within the soft tissue structures that resist internal rotation at the hip and knee joints. This storage of elastic strain energy then will cause an increased tendency toward developing abductory twist when the elastic strain energy is released into rapid external femoral/tibial rotation at heel off.

    You may want to check out my video on abductory twist on YouTube.

    Last edited by a moderator: Sep 22, 2016
  12. Apollus

    Apollus Member

    wow kevin that's your video! i watched it last week great explanation of abductory twist, thanks :)
  13. Apollus:

    Yep....the video is of a Biomechanics PhD patient of mine taken at the gait lab at Shriner's Hospital in Sacramento.
  14. Angel87

    Angel87 Welcome New Poster

    Hello All.. I am student in University of wales.. doing gait is really interesting but sometimes hard. What I want to know is determinants of gait i have it hard to understand, one more question why do we need determinants of gait and hw are we applyin to the patients maybe then i wuld get it.
    Thank you

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