Bruce,
What I am asking is does the increased stride length from a valgus fore
foot post result from:
1. An increase in firing of the gastrocnemius (as Kevin suggests).
2. Or an increase in midtarsal pronation so there compensation for the
ankle joints sagittal plane motion, and hence a longer stride length.
You have answered that with a shorter midstance, there is less MTJ
compensation, more foot stability and a longer stride as a result of hip
extension (and 1st MPJ dorsiflexion).
So you are saying that MTJ pronation limits hip extension. Can I assume
this is because external rotation of the femur allows for more hip
extension? If this is correct, then forefoot valgus posts would have to
work by causing more external rotation of the femur. Is this what you see?
Respectfully,
Stanley
At 08:15 AM 12/7/04 -0600, you wrote:
>Stan;
> Please let me know if I'm not contributing what you want exactly. I've
>been following this thread loosely at best.
> Determining whether a valgus or varus FF post or pad will increae the
>midstance or propulsive phase is very difficult, and enigmatic at times.
>You must understand that just because there is a prolonged midstance phase
>in a foot that pronates longer, due to FnHL etc., that shortening the
>midstance phase will not necessarily prolong the propulsive phase. The
>timing may indeed be very closely the same for propulsion, not always, but
>often.
> I think that what Dr. Beekman my be getting at is that the valgus pad
>should increase the pressure sub 1st mpj and as I've said before allow the
>medial column to be more stable and provide for a more uniform pattern of
>F/T curves from heel strike to toe off.
> In my opinion, the firing of the gastroc has little to no effect on the
>outcome use in the example. The gastrocs ability to fire has not changed,
>only the foots ability to "roll" thru midstance in a uniform manner has been
>changed.
> So long as the midstance period is "shortened" and more uniform, the MTJ
>will need to compensate the AJ much less and therefore provide much more
>intrinsic stablity to the foot for forward momentum. This leads to a longer
>hip extension and a later knee flexion, more closely tied to the 1st mpj
>extension, and this will increase the stride length.
>Sincerely;
>Bruce Williams
>
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