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  • Quote:

    One of the problems associated with machine gait analysis is that you don't know if the pain caused the gait or the gait caused the pain.  Limping creates some very unusual gait patterns on these machines. 

     

    Eric


    Hi Eric and thanks for the response.  

    We certainly agree on recording gait with active pathology as being problematic, although the ability for comparative analysis after problem resolution can be quite enlightening with regards to mechanical compensation.


    Jay

     

       

  • Quote: Hey Eric;

     

    I am referring to the CoP composite graph produced by Noraxon's FDM-T or Gaitscan's dynamic gait line graph, where CoP is plotted on the horizonal axis and time on the vertical. Your last statement is really what I am after, you say that it is probably not related to ankle shear but clinically, 30 years later,(and theoretically as proposed), I see all the indicia.  Let's look at another example, I have seen this phenomenon in ataxic gait and some specific neurological gait patterns.  In some cases, the toes seem to be feeling for orientation before resting in midstance, I would argue that the foot is moving backwards ant/posteriorly after initial contact and the body is moving forward as the CoP graphs described earlier show, on both computerized gait platforms.  Another example might be walking on stairs.  We may have our predispositions on ankle shear, but if one accepts my example, the definition of shear is being met.  As your last statement suggests, we may think, but we just don't know and I see this as significant and germain to crafting a treatment plan (gait training, othotic prescription).  And so, with respect to both points of view and considering both scenarios (yours and mine), is what lead me to ask if anyone knows of any scholarly work on the subject.


    Talk Soon    Jay

     


    I'm not familiar with the output of those systems.  However, you should be able to read the documentation for those systems to know what you are getting.   The center of pressure at a single instant in time is an x,y cooridnate.   Depending on the direction of walking relative to the plate, one of those numbers x or y is in the ap direction and the other is in the medial lateral direction.   So, if you are looking at a plot versus time in a 2d graph you must be looking at either the ap or the med-lateral change in the position of the cener of pressure over time. 

    I'm having a problem with the wording "the foot is moving backwards".  When the forefoot hits the ground first, and the ankle dorsiflexes to allow the heel to hit the ground, there will be a tiny net rearward motion of the foot relative to the ground.   This motion is in the form of a rotation about the fixed met heads (assuming that they don't slide) and the heel coming down to the ground.   This not really linear motion, but the center of mass of the foot will move posteriorly a tiny bit.  That motion will increadibly small compared to the location of center of pressure change that you see with forefoot striking then the heel striking.  The foot is not moving backward, the location of center of pressure under the foot is moving backward.   The backward movement of the center of pressure plot is just a way of showing that the forefoot hit first.   Nothing more.   The forefoot hitting first may be indicative of many different things, but I'm pretty sure that anteior posterior shear is not one of them. Using center of pressure is not a good way to measure shear motion unless there is actual sliding of the foot.


    One of the problems associated with machine gait analysis is that you don't know if the pain caused the gait or the gait caused the pain.  Limping creates some very unusual gait patterns on these machines. 

     

    Eric

  • Quote:

    Quote:
    I'm not sure what you mean by the vertical axis that is time.  When you graph time versus something else, time is usually on the horizontal axis.


    Say you were running relatively fast and you forefoot strike, then the ground dorsiflexes the ankle and the heel touches the ground.  In this situation, at contact, the center of pressure would be under the forefoot.  Later, when the heel touches the average point of force would be pulled posteriorly.  As I understand it, this is the "retrograde motion of the COP path" that you are talking about.   However, in the next step, while you are running, you contract the calf muscles with a tiny bit more force and the heel does not touch the ground.  In this situation you would not see the retrograde motion of the CoP path.  There is very little mechanical difference between these two situations.   I would bet that the anterior posterior shear forces would be almost identical and the forward momentum would be almost identical. In answer to the question: When you see the posterior movement of the center of pressure path, this does not mean that the foot is moving backward.  It only means that the average point of contact is moving backward.  So, yes, you can see an anterior to posterior movement of the center of pressure over time.  However, it probably is not realted to ground or ankle shear.

    Hey Eric;

     

    I am referring to the CoP composite graph produced by Noraxon's FDM-T or Gaitscan's dynamic gait line graph, where CoP is plotted on the horizonal axis and time on the vertical. Your last statement is really what I am after, you say that it is probably not related to ankle shear but clinically, 30 years later,(and theoretically as proposed), I see all the indicia.  Let's look at another example, I have seen this phenomenon in ataxic gait and some specific neurological gait patterns.  In some cases, the toes seem to be feeling for orientation before resting in midstance, I would argue that the foot is moving backwards ant/posteriorly after initial contact and the body is moving forward as the CoP graphs described earlier show, on both computerized gait platforms.  Another example might be walking on stairs.  We may have our predispositions on ankle shear, but if one accepts my example, the definition of shear is being met.  As your last statement suggests, we may think, but we just don't know and I see this as significant and germain to crafting a treatment plan (gait training, othotic prescription).  And so, with respect to both points of view and considering both scenarios (yours and mine), is what lead me to ask if anyone knows of any scholarly work on the subject.


    Talk Soon    Jay

     



  • Quote:

    Hi there Eric: Quote "Hi Jay, For examining shear you should not look at the center of pressure path and you should look at medial to lateral and anterior to posterior forces. These forces can be examined using some specialized force platforms. Many platforms don't measure ap and ml shear. A platform, or inshoe sensor that measures pressure over discrete areas can be used to calculate the center of pressure of vertical force. The center of pressure of vertical force is just the average point of vertical force. The center of pressure path is just a picture with the location of the center of pressure over time. The direction of the center of pressure path over time is independent of shear forces. I described center of pressure in my 1999 JAPMA paper. " I agree with this protocol but I was raising a different point. I used the "c.o.p." graph as a way of saying that I have recorded moments where, along the vertical axis that is time, "cop" is tracking backwards. The reason for my original question was to find out if anyone has discussed this phenomenon. Eric, would you agree that such moments of retrograde motion exist, and if so, when time and body momentum are moving forward, and, in say toe to heel patterns, the foot is moving backward in certain moments, isn't that shear at the ankle joint. Two divergent forces moving on the same plane? Jay

    I'm going to assume that when you refer to moments above you are referring to an instant in time rather than the torque meaning of moment.  I'm not sure what you mean by the vertical axis that is time.  When you graph time versus something else, time is usually on the horizontal axis.


    Say you were running relatively fast and you forefoot strike, then the ground dorsiflexes the ankle and the heel touches the ground.  In this situation, at contact, the center of pressure would be under the forefoot.  Later, when the heel touches the average point of force would be pulled posteriorly.  As I understand it, this is the "retrograde motion of the COP path" that you are talking about.   However, in the next step, while you are running, you contract the calf muscles with a tiny bit more force and the heel does not touch the ground.  In this situation you would not see the retrograde motion of the CoP path.  There is very little mechanical difference between these two situations.   I would bet that the anterior posterior shear forces would be almost identical and the forward momentum would be almost identical. In answer to the question: When you see the posterior movement of the center of pressure path, this does not mean that the foot is moving backward.  It only means that the average point of contact is moving backward.  So, yes, you can see an anterior to posterior movement of the center of pressure over time.  However, it probably is not realted to ground or ankle shear.

    Eric

  • Hi there Eric:

    Quote
    "Hi Jay,

    For examining shear you should not look at the center of pressure path and you should look at medial to lateral and anterior to posterior forces. These forces can be examined using some specialized force platforms. Many platforms don't measure ap and ml shear. A platform, or inshoe sensor that measures pressure over discrete areas can be used to calculate the center of pressure of vertical force. The center of pressure of vertical force is just the average point of vertical force. The center of pressure path is just a picture with the location of the center of pressure over time. The direction of the center of pressure path over time is independent of shear forces. I described center of pressure in my 1999 JAPMA paper. "

    I agree with this protocol but I was raising a different point. I used the "c.o.p." graph as a way of saying that I have recorded moments where, along the vertical axis that is time, "cop" is tracking backwards. The reason for my original question was to find out if anyone has discussed this phenomenon. Eric, would you agree that such moments of retrograde motion exist, and if so, when time and body momentum are moving forward, and, in say toe to heel patterns, the foot is moving backward in certain moments, isn't that shear at the ankle joint. Two divergent forces moving on the same plane?

    Jay
  • Quote:

    Hi Dennis,

    Yes, largely that's true, especially when adding mods like rearfoot varus posts, but it does depend on foot type, existing foot conditions, and biomechanical abnormalities.  Since motion and stasis require different muscular engagement and demands on the musculoskeletal system, one relatively supinates the static foot to control pronation in forward motion, which is, as you say Dennis, problematic for other walking patterns and general stasis. 

    Jay, it is helpful to quote the part of the previous posters statement that you agree with.  If you were referrring to: "If correct, wouldn't that logically imply that treating The Gait Cycle may in fact be creating harmful forces when applied to other lifestyle activities?" I'd say that statement is correct around half of the time.  I occaisionally get sinus tarsi pain.  Orthotics with a medial heel skive and a rearfoot post help that both in straight ahead gait and in side to side motion sports.  

    That does raise the interesting question of when, and why, your normal orthotics should be modified for specific activities.  I've added a high lateral plange to a fencers trailing foot orthotic because there is so much medial to lateral force in that foot.  (push off in a lunge)  Anybody have other examples?

    Eric

  • Hi Dennis,

    Yes, largely that's true, especially when adding mods like rearfoot varus posts, but it does depend on foot type, existing foot conditions, and biomechanical abnormalities.  Since motion and stasis require different muscular engagement and demands on the musculoskeletal system, one relatively supinates the static foot to control pronation in forward motion, which is, as you say Dennis, problematic for other walking patterns and general stasis. 

  • Quote:

    Jay:

    Am I correct in stating that you theorize that when a person is walking toe-heel instead of heel-toe, the physics/forces of that activity may be/is different than the physics of The Gait Cycle.

    and

    When a chef moves side to side along his cooking surface, the physics/forces of that movement are different to the other two?

    and if I were in the gym doing a 300 press while in stance, the physics/forces of that movement are different than the other three?

     

    If correct, wouldn't that logically imply that treating The Gait Cycle may in fact be creating harmful forces when applied to other lifestyle activities?

    Dennis

    Not necessarily.   Treating high forces seen in heel to toe gait may also help reduce forces in side to side motions.  A long 2nd metatarsal will tend to have higher forces on it when compared to other types of feet regardless of the type of weight bearing activity.   Reducing force on an injured anatomical structure should help that structure in any activity. 

    Eric

  • Quote:

    Hi Eric;

    Thanks for the response.  By retrograde motion I mean tracking movement contrary to momentum by way of gait line graphings of center of pressure.  For instance, if one landed on the forefoot or midfoot, then settled back on the heel while momuntum (and the body itself) was striding forward, this would appear to create shear at the ankle joint as the foot motion is going backward while the body is moving forward.  I have tracked this with forefoot strikers while running and in oblique walking such as a chef would do in a commercial kitchen.  Are you familiar with any studies dealing with these type of scenarios?

     

    Best Regards,   Jay

    Hi Jay,

    For examining shear you should not look at the center of pressure path and you should look at medial to lateral and anterior to posterior forces.  These forces can be examined using some specialized force platforms.  Many platforms don't measure ap and ml shear.  A platform, or inshoe sensor that measures pressure over discrete areas can be used to calculate the center of pressure of vertical force.  The center of pressure of vertical force is just the average point of vertical force.   The center of pressure path is just a picture with the location of the center of pressure over time.   The direction of the center of pressure path over time is independent of shear forces.   I described center of pressure in my 1999 JAPMA paper.

     

    Eric

  • Jay:

    Am I correct in stating that you theorize that when a person is walking toe-heel instead of heel-toe, the physics/forces of that activity may be/is different than the physics of The Gait Cycle.

    and

    When a chef moves side to side along his cooking surface, the physics/forces of that movement are different to the other two?

    and if I were in the gym doing a 300 press while in stance, the physics/forces of that movement are different than the other three?

     

    If correct, wouldn't that logically imply that treating The Gait Cycle may in fact be creating harmful forces when applied to other lifestyle activities?

    Dennis

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