Hi all,

Kevin replied to Bob:
><<Can anyone think of a simple way to measure toe flexion power but taking
>the fascial windlass effect out of the equation.  I have a few ideas but
>would appreciate some collective thinking.>>
>
>If I were to tackle this experimentally, I would first assume that, during
>standing, the plantar fascia is the only structure that is contributing a
>certain magnitude of passive plantarflexion moment to the
>metatarsophalangeal joint (MPJ).  It is this passive plantar fascial
>tension that maintains digital purchase force in relaxed bipedal standing
>(I think that this may be the case in most feet during relaxed bipedal
>stance when the individual is balanced so that their center of mass is not
>too anterior to their ankle joint axis).
>
>Then, from a baseline measurement of the digital purchase force in relaxed
>bipedal stance(which would account for the tensile force within the
>plantar fascia) one could then have the subject volitionally plantarflex
>the digits harder against either a pressure mat or other type of force
>transducing system to assess the plantarflexion moment that is contributed
>by the active contractile elements that produce a MPJ  plantarflexion
>moment.  Subtracting the baseline contribution of the plantar fascial
>passive MPJ plantarflexion moment  from the total plantarflexion moment at
>the MPJ caused by the plantar fascia and the MPJ plantarflexors during a
>volitional maximal contraction should give you a good approximation of the
>maximum force the digital flexors can achieve at each of the five MPJs.
>
>This assessment could also be done in a non-weightbearing setting but I
>believe that this would not be as functionally relevant due to the change
>in the length-tension relationship of the plantar intrinsics and extrinsic
>flexors that occurs with the increase in length of the longitudinal arches
>due to loading of the midtarsal-midfoot joints with normal weightbearing
>forces.
>

You have to be careful in redundant situations.  The fascia has essentially
an identical function as abductor hallucis.  In this situation, as you
increase the tension in the abductor hallucis there will be a decrease in
the tension in the fascia, assuming everything else remains the same.

Speaking of everything else remaining the same, you would also have to
carefully watch body position.  As the subject leans forward there will be
an increase in tension in the Achilles tendon, which increases the bending
moment on the foot, which could lead to an increase in plantar fascial tension.


Cheers,

Eric Fuller

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