Hi all,

Kevin Miller wrote:

>
>Dr. Stanley Beekman said this better than I...."My simplistic
>understanding of gait is that the lifting of the leg puts the energy in
>the system, and the body utilizes this energy via eccentric muscle
>contractions to provide forward motion.  Wouldn't we have a hip flexor
>(ilio-psoas) function eccentrically to provide the external
>rotation?"  This is exactly my point with one exception.  The plantar
>flexors, aided by the windlass, lift the COM in the gravitational
>field.  The reason I put emphasis on the windlass mechanism is because the
>plantar flexors will plantar flex the foot even if the COM is NOT
>raised.  In short, the windlass is the key to generating the potential
>energy.  (Gravitational potential energy is a product of weight and
>vertical displacement.)  Flexing the hips independently does little to
>change COM position.  But a mass as great as a leg moving vertically
>generates enough momentum to ease ! the burden on the planter flexors and
>the windlass.  In short, the magnitude of vertical displacement of the COM
>will be the sum of the forces created by hip flexion and plantar flexion
>acting around a lever created by the windlass mechanism.  The implication
>is that a maximum force will still yield little in the way of
>gravitational potential energy if the lever arm is not sufficiently
>long.  Add to this the timing issues already mentioned, and proper
>formation of the windlass becomes obvious for the MOST efficient
>gait.  However, as I mentioned in the earlier post, fail-safe mechanisms
>will activate to keep the organism ambulating until its limit for
>compensation is reached.

Kevin M., I think you are saying that the windlass helps propulsion by
providing a rigid lever.  I would agree with this with the addition that
the windlass does not even have to wind to add rigidity to the foot.

>
>Eric wrote: "The fascia is oriented vertically and is
>ideally positioned to prevent adduction of the tibia on the femur and the
>femur on the hip. Any twist in the tibia would just twist the fascia
>latta. Fascia has very little torsional stiffness"
>
>Exactly, Eric.  But remember, the most sturdy fibers extend all the way
>across the tibial tubercle, i.e., past the midline of the tibia, where
>tibial torsion due to failure of the windlass results in an eccentric
>external rotation and abduction moment.

The original question was related to the ability of hip muscles to cause
supination of the STJ.  For this to happen there has to be little movement,
in the transverse plane between the femur and the tibia.  The proximal
attachment of the Ilio Tibial band is so far away from the knee that I
doubt that it could significantly effect transverse rotation of the
knee.  It would seem that as you rotate the tibia on the femur you would
just twist the fascial band, without much resistance.  Anybody read any
good articles about which structures prevent transverse plane rotation at
the knee?


Cheers,

Eric Fuller

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