Bruce,
Could you provide details of the sample employed in the study by
Gracovetsky.
Thanks,
Simon
----- Original Message -----
From: "Bruce Williams" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, May 19, 2002 3:48 PM
Subject: Re: case of hallux RIGIDUS
> Eric;
> Gracovetsky says the following: " Earlier we discussed how the
potential
> energy of the trunk is converted to kinetic and then elastic potential
> energy at heel-strike. A quantitative measure of just how much energy is
> liberated can also be derived from the data of Cappozzo(1983) and Thurston
> and Harris (1983). Again, dividing the displacements of the upper body in
> the lateral sagittal planes by five to obtain the average displacement per
> joint in the lumbar region ( but this time asuming the thoracic IV joints
to
> be relatively stiff in these planes), we can calculate the average
> mechanical work per joint done on the upper body to overcome inertia. The
> results of such calculations are shown in Fig. 10.12. Note the large
> negative value of work done in the lateral plane at heel-strike; this
> indicates that mechanical energy is released by the upper body at this
> stage.
> Unfortunately, such data provide no way of deciding exactly where this
> energy goes. Our hypothesis is that theis energy is not wasted, but that
> most of it is stored as elastic potential energy in the lumbodorsal fascia
> and subsequ3ently recovered to rotate the pelvis via the coupled motion.
> The calculations given in Figs. 10.23-10.25, which show a large power
> absorption pulse for rotation in the transverse plane appearing shortly
> after heel -strike, are consistent with this hypothesis."
> Hope this helps.
> Bruce
> ----- Original Message -----
> From: <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Sunday, May 19, 2002 2:45 AM
> Subject: Re: case of hallux RIGIDUS
>
>
> > Howard writes:
> >
> > <<<
> > Glad to hear that my comments are essentially in agreement w/ Winter.
The
> > significance of the peak in thrust is to point out how the power is
> created,
> > not necessarily how it is utilized. The peak is reached by the end of
> single
> > support phase. Momentum will continue to produce longitudinal ground
> shear
> > through the 1st half of double support phase. Hence the positive nature
> of
> > the shear graph from mid single support through mid double support.
Since
> > the braking and thrusting require some time to transition from one to
the
> > other, the timing from peak braking to peak thrusting is important in
the
> > overall understanding of how we create the power to walk. Since the
peaks
> > occur in precise timing to the onset and termination of single support
> phase,
> > it would seem difficult to ignore the effect of the swing limb's
function
> on
> > power development.
> > >>>
> >
> > Howard, I think I understand a little better where you are coming from.
> I
> > have been looking at ground shear from a slightly different perspective.
> > Ground reactive shear can result from the relationship of the center of
> > pressure to the center of mass. The swing leg, as part of the center of
> mass
> > will effect the position of the center of mass. When the center of mass
> is
> > anterior to the center of pressure, the body will rotate forward. With
> > enough friction from the ground the foot will stay in the same place and
> the
> > face will fall flat on the ground. Without friction, the feet will
slide
> > backward and the face will fall flat on the ground. The friction will
> allow
> > the body to push against the ground, creating thrust, when the center of
> mass
> > is anterior to the center of pressure. However, there is more than one
> > possible source of ground reactive shear. Another source of ground
> reactive
> > shear is muscular push off. Think of a sprinter in a starting blocks,
the
> > sprinter can create ground active shear with muscular power with muscle
> > activity at either the hip, knee, or ankle. The thing that is really
> > exciting about inverse dynamic and energy calculations is that you can
> figure
> > out where the power contribution comes from. The body has a certain
> amount
> > of energy. The energy can either be in the form of kinetic (motion)
> > potential (height) or chemical (muscular). Power is the rate of change
of
> > energy. Chemical energy (muscles) can be used to add energy or remove
> energy
> > from the body. When you jump up you gain potential energy. As you
fall
> you
> > lose your potential energy and convert it to kinetic energy. When you
> land
> > you absorb that kinetic energy into muscular activity. With each step
> there
> > is simultaneous braking (contact limb) and acceleration (propulsive)
limb.
> > Each time energy is lost it must be added again to maintain the
velocity.
> > Winter's analysis of gait shows that there is a cycling of potential and
> > kinetic energy. At the end of double support to the middle of single
> support
> > the body has to gain elevation and Winter measured that there was a
> decrease
> > in forward velocity (kinetic energy) as this occurred. And then the
> > potential energy was converted back into kinetic energy from the middle
of
> > single support into double support as the body falls forward and looses
> > height. The highest point is when the body is over the stance leg and
the
> > lowest is when there is equal weight on both feet. The above describes
> whole
> > body energetics.
> >
> > Lower limb energetics are a little different because the limb
essentially
> > starts and stops every step and hence there is a lot of energy change in
> the
> > leg. At heel contact the kinetic energy of the leg is absorbed into
> muscular
> > contraction (ant tib, quads) and the leg loses both kinetic and
potential
> > energy. Prior to the initiation of swing energy has to be added back to
> the
> > leg from some source. Perhaps, there is some energy stored elastically
in
> > the spinal engine, but it cannot be the total amount lost because some
is
> > lost to energy absorption in muscular contraction. It has been a while
> since
> > I read the spinal engine, is part of the elastic chain muscular? Does
> > passive muscle stretch and return need some addition of chemical energy?
> > Does the spinal engine always store energy every step and must it use
this
> > energy to swing the leg forward every step? What if you all of a sudden
> > notice that you don't want step where your next natural step would put
> your
> > foot. Do you have to fight the spinal engine in this case. Is this an
> > evolutionary advantage?
> >
> > Anyway the faster the swing leg moves the more energy was put into it.
If
> > you see a much faster gait (or swing phase) it would make sense that
more
> > than one source of energy was responsible for making it swing faster.
If
> > your treatment changed the gait from one which there was no ankle
plantar
> > flexion to a gait where there was ankle plantar flexion and the swing
leg
> was
> > moving faster, then there is a pretty good chance that increased ankle
> power
> > was partly responsible for the faster swing.
> >
> > Cheers,
> >
> > Eric Fuller
> >
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