RE: Stability Maneuver (Dwight L. Bates, DPM)
From: Multiple Respondents
This maneuver is used commonly by individuals
attempting to "prove" to an unsuspecting public
that the foot inserts that they are standing on
give them "increased foot stability." The
physics of this maneuver, like most "magic
tricks," is quite simple, but also quite clever.
The subject is first asked to stand without the
inserts under their feet with their hands palm
up in front of their bodies, with their forearms
horizontal. The salesman then applies a force
with their hands in a vertical direction onto
the subject's hands. Since the axis of rotation
with the ground for a standing individual is at
their plantar feet, and since the salesman's
applied force vector is directed anterior to
this axis of rotation at the plantar feet, the
applied force from the salesman will cause a
rotational force (i.e., moment) that will tend
to make the subject rotate forward at their
feet, thus tending to make the subject lose
their balance forward and feel "unstable."
Next, the subject is asked to stand on top of
both of the shoe inserts, again with their
forearms horizontal and hands palm up. The
salesman then applies what he says is the same
force to the subject's hands. The salesman now,
however, instead of applying a directly vertical
force, is making sure he is applying a vertical
and slightly posteriorally-directed force into
the subject’s hands. Since the applied force
vector from the salesman now is directed toward
the feet of the subject, instead of anterior to
the feet as before, the subject will not
experience any rotational force that will make
him tend to lose their balance forward. The
subject will only feel their feet pressing more
firmly onto the shoe inserts, thus imparting a
sense of "stability" from the shoe inserts.
Kevin A. Kirby, DPM, Sacramento, CA,
The maneuver is supposed to be an applied
kinesiology test. The muscle test and the
accuracy of it is the key to this discipline. It
is not easy to do accurately, and requires
practice and skill. The muscle test is looking
for the ability of the muscle to summate, not
necessarily strength. When a muscle summates, it
locks. When it is not summating, you can feel
the fibers slide. Dysponesis can alter the
results.
The problem with the test described, is a
patient/subject can easily recruit other
muscles. A little twist of the body, and the
patient/subject can easily recruit the
supraspinatus. For this reason, more commonly
the infraspinatus muscle is tested in the upper
extremity.
The trick with this test is that if the
patient/subject is not given enough time to
recruit the muscle, the muscle will not be able
to summate. Properly performed, the
patient/subject would have to press against the
examiners hand to contract the muscle before the
examiner gradually increases the force. If the
examiner starts to increase the force before the
patient/subject can contract the muscle fully,
then there will be failure. Another way to
influence the test is to say something to the
patient/subject just about the time the test is
to be performed. This will distract the subject,
so a full contraction will not occur.
Stanley Beekman, DPM, Cleveland, OH
This reminds me of the parlor trick
of "levitation." A group of people place their
hands beneath the thighs of a seated person and
attempt to lift him. Difficult. Then they hold
their hands out above his head, steady, for a
few minutes. Then they lift him again. He goes
up as easily as a feather. Try it.
The baloney explanation consists of energy
fields, auras, etc. I don't know the real
explanation, but I suspect that the act of
preparing to lift, with everyone holding out
their arms, concentrating, breathing, makes each
person's individual effort on the second attempt
a bit more efficient and the combined effort a
bit more synchronized. All of that
makes for a dramatically easier lift. Something
similar here is probably at work.
Steven D Epstein, DPM, Lebanon, PA,
sdepstein@yahoo.com
