Eric, Stanley and Kevin K.;
    I have to agree with Stanley on this one Eric.  I will not argue the
elements of forces you describe w/ the Nutcracker analogy, but I do have
some questions.  One of them pertains to Kevin's Kinetic / Kinematic
discussion.
    Since you compared the pressure on the nut to the STJ, I will use that
as the basis for my question.  What causes the pressure of the nutcrackers
mouth or hands on the nut?  It has to be the lever at the nutcrackers back,
and this will be caused by pressure from somones hand and there arm, etc.
    If that is the case, then your example is skewed.  I get your point, and
I think it is well meaning.  But, the problem lies in explaining why the arm
and hand on the lever of the nutcracker are no longer needing to push down,
i.e. to "crack that particular nut!"  Pun fully intended! ;-)
    In other words, what exactly has caused the AJ to dorsiflex more, and
the MTJ to stop pronating, thereby decreaseing the pressure on the STJ
(nut)?  And, for this to truly happen, you have to have motion at these
other areas decrease or increase!, by some degree, i.e. kinematics -
measureable or not, to drive the change in the kinetic forces.
    For any kinetic change at one measureable are, such as the STJ,
something has to have happend elsewhere.  We are not talking about magic, it
is mostly physics afterall!  This is why I FEM is too advanced for most
computers at this time.  There is not enough computer power to calculate the
changes at the AJ, and each segment of teh MTJ, and the position of the STJ,
let alon the forces caused by the metatarsals, and fibula and tibia!  Sorry
for the abreviations, but they are usual.
    As for kinematics, I'll not argue that reliably measuring the motion at
any of the segments I mentioned can be difficult, it still can and has to be
done.  I think it has been easier to focus on the calcaneus and teh STJ,
because that was and still is what most people feel drives all pathology of
teh foot.  I think that is changing, and as more reliable measures become
commonplace w/ kinematics, we should find more repeatable studies published
that will add worlds to the explanations of why the kinetic forces have
changed in certain areas such as the STJ.
Sincerely and not quite sleepily!
Bruce


----- Original Message -----
From: "Dr. Stanley Beekman" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, December 16, 2004 1:10 AM
Subject: Re: EVA vs Plastic/Carbon Fibre FFO's: Discuss


> Eric,
>
> You wrote:
>
> >There can be a change in R, and moment, without a change in position.  I
> >have always liked the nutcracker analogy.  Place a nut so that it touches
> >one arm of a nutcracker.  Now slowly move the other arm so that it also
> >touches the nut.  (This is analogous to the maximally pronated
> >position.)  Now squeeze harder.  The position of the nut has not changed
> >relative to the arms of the nutcracker.  The force, and stress, on the
nut
> >has changed.
>
> Thanks for explaining this to me. But I am now further confused. My
limited
> knowledge on the subject is RXF.
> Radius times Force. Since we are not changing Radius, we must be changing
> Force, which is what I seem to understand from your analogy. Since force
is
> a function of body weight, and body weight has not changed (unless too
many
> nuts have been eaten), where exactly does this increase in force come
from.
>
> I will stop eating nuts until this is explained to me.
>
> Sincerely,
>
> Stanley
>
>
>
>
>
> >Good eating,
> >
> >Eric Fuller
> >
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