Dear all,
First, I would like to thank Kevin for his kind words.
When we began this project and for the first couple
of years, we were essentially in the dark so far as
positive reinforcement. I can say that this
discussion is certainly giving me the "steam"
necessary to press onward. Thanks again.
I would like to make a couple of comments regarding
speed and axial load of the DGR (Dynamic Gait
Replicator). It does indeed function at slower than
normal gait velocity, approximately one half speed.
It is essential a slow "Sunday stroll". One can
actually walk at the same speed that the DGR functions
but it is not average human gait speed. Future
studies will have the DGR working at full speed after
some minor adjustments to the machine.
As for axial load, the DGR is capable of applying just
over 100 KG or 980N. We began by setting the
pneumatic regulator to replicate the weight found in
the vital statistics provided with each cadaver
specimen. We did find that the feet functioned more
naturally when slightly greater than "live weight" was
applied. This increase may just make up for the
reduced force of half-speed gait. The reduced speed
certainly does reduce inertial force so increasing the
load seems to make up for that to some extent. As we
had stated before, it is a work in progress.
That's about all I can conjure up at this late hour.
Cheers,
Jay
--- Kevin Kirby <[log in to unmask]> wrote:
> Chris, Erin, Jay and Colleagues:
>
> First of all, I commend Chris, Erin, Jay and Daryl
> for their work with the Dynamic Gait Replicator
> (DGR). The first time I saw the replicator in
> action (with Erin showing Chris and I videos of it
> in action at a hotel room on his laptop computer a
> few years ago) my mouth dropped open....I was very,
> very impressed in how lifelike the foot and lower
> extremity moved. I still can't imagine all the
> hours of work that went into it and think it is
> probably one of the most impressive biomechanics
> projects that any group of podiatrists has ever
> undertaken and completed.
>
> However, I have a few more points about the DGR that
> may affect its simulation of a person walking. In
> addition to the lack of intrinsic muscle activity
> mentioned earlier, I know that the DGR "walks"
> significantly slower than normal gait and would
> think that this may affect the kinematics of the
> bones of the foot during the stance phase of gait.
> If I am not mistaken, doesn't the DGR also walk with
> less magnitude of ground reaction force plantar to
> the foot than occurs in a normal sized individual? I
> would think that if this is the case that the
> kinematic results may change as a result of
> differences of loading forces on the plantar foot.
>
> Jay wrote:
>
> <<On control: Initially, we controlled more
> forcefully the sagital, transverse, and frontal
> planes. We were not satisfied with the resulting
> gait pattern. Through trial and error, we stumbled
> upon an interesting and important fact. The more we
> controlled, the poorer the function. The less we
> controlled, the more natural was the apparent gait.
> We found that by just controlling extrinsic
> function/timing, forward progression, and axial
> loads leaving freedom of motion in other planes, we
> were able to get the best results. Since every foot
> functioned differently in life, to force it to
> walk"properly" was hopeless. To allow it to walk as
> it "wished", was effective.>>
>
> I loved this comment from Jay. Here is the lesson I
> think we can learn from Jay's experimental
> observation. Any "control" exerted proximally on
> the tibia from the DGR means that rotational forces
> (i.e. moments) are being applied to the tibia from
> the DGR. However, in the real human being, the
> forces that control the kinematics of the foot
> during the stance phase of gait are probably more
> the result of the interaction of the foot with the
> ground, not a result of the proximal forces on the
> tibia. Any attempt to let the DGR "control" the
> proximal tibia may have caused abnormal moments to
> be applied to the proximal tibia rather than
> allowing the tibial moments to be generated
> primarily from the ground reaction force (GRF), as
> they are in the real human foot. This observation
> may have important implications as to why foot
> orthoses, that exert their primary mechanical effect
> on the temporal patterns, locations and magnitude of
> GRF, can have such a significant effect on the
> function of the foot and of the whole lower
> extremity. I believe that Jay's observation also
> ties in with Benno Nigg's theory of Preferred
> Movement Pathway and why this occurs (or doesn't
> occur) in the human foot and lower extremity.
>
> Thanks to Erin, Jay and Chris for contributing and
> am looking forward to their further contributions on
> these subjects.
>
> Cheers,
>
> Kevin
>
>
****************************************************************************
> Kevin A. Kirby, DPM
> Adjunct Associate Professor
> Department of Applied Biomechanics
> California School of Podiatric Medicine at Samuel
> Merritt College
>
> Private Practice:
> 107 Scripps Drive, Suite 200
> Sacramento, CA 95825 USA
>
> Voice: (916) 925-8111 Fax: (916) 925-8136
>
****************************************************************************
>
>
>
>
>
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