Paul and Colleagues:

In a message dated 8/22/99 6:22:25 PM Pacific Daylight Time,
[log in to unmask] writes:

<< Thanks for your responce to my questions, I still have a problem with
 forefoot control effecting heel strike, must be a very heavy forefoot wedge
 (; (smile). The only suggestion I would make is that perhaps pre
 positioning for heel strike is effected by the postion of the foot from the
 previous Heel lift through to toe off, perhaps a better position here is
 maintained in to swing phase and there is therefore an effect on heel
 strike position???????. Sound to me like it needs some research on this
 one,  Anyone with a better explaination/theory?????? >>

As Eric mentioned, there is a growing body of research evidence which points
to the fact that the human body will change the lower extremity joint angles
during running depending on what type of surface it is running on and whether
the running is done on level ground, downhill or uphill surfaces.  This tends
to support the idea that the individual subconsciously will vary the position
of his/her lower extremity joints such as hip flexion angle, knee flexion
angle, ankle dorsiflexion angle and even the touchdown velocity depending on
the surface or slope of the surface the individual is running on.  The same
probably occurs in walking, but to a lesser extent.  I do have the references
and could probably find them eventually.

Paul, I do not see why it is so difficult to understand how changing the
position of the forefoot and rearfoot with a forefoot valgus wedge, for
example, in late stance phase would not also change the STJ pronation and
supination moments of the anterior muscle group of the leg during swing
phase.  In addition, my observations consistently show that the forefoot
valgus wedge makes the forefoot evert more to the ground during swing just to
clear the plantar forefoot from the ground during mid swing phase.

I believe that all of the above factors, in combination, contribute to the
consistent observation I have made that forefoot valgus wedging, by itself,
will alter the position of the rearfoot at heel contact (not greatly, but
slightly) when compared to no forefoot valgus wedging.

Another factor which is worth mentioning is that Benno Nigg's research group
classified the rearfoot pronation occurring during the first half of support
phase of running as being both "passive" and "active".  They felt that the
first 10% of the running support phase rearfoot pronation was related to
touchdown angle of the rearfoot and was uncontrollable by extrinsic muscle
function (i.e. passive).  They also felt that the rest of the rearfoot
pronation occurring in support phase was able to be controlled by extrinsic
muscle function (i.e. active).

I believe that this same phenomenon occurs, to some extent, in walking.  Many
feet with large degrees of rearfoot varus and forefoot valgus deformities
will show an initial STJ supination motion at heel contact during barefoot
walking probably due to the plantar calcaneus being so medial to the STJ axis
at heel contact.  This is probably a "passive" phenomenon which the
individual would find difficult to control with muscle function.  This is,
however, able to be modified by using lateral heel wedging (i.e. a lateral
heel skive on an orthosis) to change the point of ground contact of the
calcaneus to a more lateral position which decreases the supination moment
arm across the STJ axis at the instant of heel contact.

This is why I like teaching gait function to students, residents and
podiatrists by attaching adhesive felt padding on barefoot walking subjects
to show how altering the ground reaction forces acting on the plantar foot
can change the kinematics of the individuals walking gait pattern (then I use
these demonstrations to draw an analogy to how foot orthoses change ground
reaction force (GRF) to orthosis reaction force (ORF) on the plantar foot to
cause the same changes).  Those of you who attended my seminar in England
last year in Cheltenham saw first hand how dramatic these changes can be with
simple adhesive felt padding added to the plantar feet of the subjects.

Cheers,

Kevin

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Kevin A. Kirby, D.P.M.
Assistant Clinical Professor of Biomechanics
California College of Podiatric Medicine

Private Practice:

2626 N Street
Sacramento, CA  95816
Voice:  (916) 456-4768   Fax:  (916) 451-6014
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