Dr. Rothbart graciously wrote me back via email (he lost his password for the forum) with responses to the questions I posed above. Here is his email:
* What is the evidence that the postural change is a result of a
feedback loop and not just a result of the shift of center of mass?
We don't know. It could be either. However, if it was due to a shift
in the center of mass, then one would expect a 1:1 ratio (geometry of
material:amount of shift in COM). However, this is not what we see. The
first 3mm gives us an approx 70% improvement in the COM (towards
verticality). This would be inconsistent with simply a mechanical support
model.
* Following up the previous question, how can the two variables
(feedback loop or COM shift) be examined independently to determine which
one is indeed the factor contributing to the postural realignment? It would
seem that the proposed mechanism (feedback loop) is a result of the shift in
COM and thus cannot be cited as the mechanism of postural change.
This question has been debated heavily by the French Posturologists (Gagey,
Bricot, Willem). Several excellent textbooks have been written on this
subject (let me know if you want the titles). The consensus of view is that
we are dealing with a feedback loop in the plantar receptors of the foot
that produce the postural shift.
* Is there any force data (inverse dynamics, force plate, etc.) to
examine possible kinetic changes in gait as a result of the inserts?
Yes. My paper presents preliminary information looking at the media
pressure and surface area readings plus changes in the postural sway. We
find the postural tonicity normalizing when appropriate proprioceptive
insoles are used. Conversely, we find the media pressure readings
(indicator of postural tonicity) becoming skewed when supportive type
orthotics are used. This is very similar to Fusco's research (Italian
Posturologist) which demonstrated an unleveling of the pelvis and increase
in spinal curves using supportive orthotics (she used 3d VRs Formetrics to
compile her data).
* Would it be possible to use foot pressure analysis (insole strain
gauge, pedar, etc.) with the medial post to look at the effect it has on
foot pressure through the gait cycle or standing posture or would the foot
presssure insert disturb the function of the medial post?
Unfortunately it wouldn't work. We take all our readings barefooted. That
is, the patient walks in the proprioceptive insole for 5 minutes or so, and
then stands barefooted on the pressure plate. This demonstrates the memory
the body has to these plantar tactile stims (emgrams).
* Is there a concern that the medial post would place a greater load
on the first metatarsal, as this bone is already prone to stress fractures.
This doesn't happen because we are not lifting the 1st metatarsal. In
Primus Metatarsus Supinatus, the 1st metatarsal is structurally elevated
when the foot is placed in STJ nP. We are simply providing a tactile stim
under the 1st metatarsal to direct (not support) the foot to function in a
more vertically aligned position.
* Is there typically an immediate (hopefully acute) decrease in
athletic performance due the person having to readjust motor patterns
learned without the medial post?
Just the opposite. We find an immediate, significant improvement in
performance as body mechanics become more linear.
* In your above post, you said you used pressure plate analysis to
examine the compensation of the muscles. Can you please clarify, is this
conclusion based on what you're thinking is happening and not something that
is directly observed from the data?
We use media pressure readings as an indication of postural tonicity. Since
w
e are recording plantar responses, in reality we are looking at the
posterior postural chain (foot to head). What we are seeing is: (1) a
normalization of media pressure readings with proprioceptive insoles
(indicating a decrease in postural tonicity), a skewing of media pressure
readings with supportive orthotics (increase in postural tonicity). This
correlates closely to motion/palpation studies and subjective outcome
studies.
If you would like to read my current paper (presently in peer review for
publication), let me know. You can read my prior papers at the website
listed below. Look under white papers.
Best Regards,
Brian Rothbart
