Posturology - Fact or Fiction?

[rothbart]

In the thread on the Clubby Wedge, Robert wrote "A while ago you may remember that i invited brian to provide the full text (or link thereto) of a kinematic, kinetic or outcome based study on the proprioception concept so that we could review some solid evidence. Perhaps that would be a fertile ground upon which to move forward."

Let's start this discussion by examining one of the pivotal underpinnings of Posturology, that is, by putting a stimulation underneath the foot (be it tactile, vibratory etc) the posture will automatically adjust.

Kavounoudias, Roll etc al (Journal of Physiology) wrote an interesting paper (available on the web) that looked at this very issue. You can access this study at jp.physoc.org/cgi/content/full/532/3/869

Robert, why don't you open the discussion as devil advocate and present an argument challenging this research.

Pror B

[robertisaacs]

Nice one Brian, good thread. Interesting article

I've only skimmed it as yet, i shall go through it properly when i get time. It deserves more than a 10 minute scan.

As a preliminary, several things jump straight out which, perhaps, you can clarify for me before we get started in ernest.

1.

Evidence for an interaction between information from multiple sensory sources also comes from numerous studies showing, for instance, that the direction of the postural responses induced by either visual (Wosley et al. 1996) or vestibular (Lund & Broberg, 1983; Ivanenko et al. 1999) stimulation varies according to the orientation of the eyes, the head and/or the trunk. These data lead to the conclusion that the muscular proprioceptive signals indicating the relative position of the upper body segments are jointly processed with vestibular and visual cues to organise appropriate posture.

This from the introduction

The researcher here is, like any good scientist, seeking to compare the relative significance of proprioceptive vs tactile stimulation to the maintainance of posture. To do this he isolates them by removing visual from the equation (by getting the subject to shut their eyes.

Is there any data comparing the significance of tactile to visual input and / or the "damping" effect of visual stimulus?

2.
The methodology seems to be trying to compare the effect of planter tactile sensation against proprioceptive stimulation of long muscles. (correct me if i'm wrong)

Is applying vibration stimulus to the planter surface of peoples feet (which is a stimulation not found in nature and is therefore alien) equivilent to applying increased pressure on a certain part of the foot (changing pressures being a constantly fluctuating variable based on the stage in gait cycle, terrain etc.).

3.
The change in posture was judged on the basis of :=

The latency of the whole-body sways was considered as being equivalent to the onset of the ankle angle deviations from the vertical because the body always oscillated in the sagittal plane as an 'inverted pendulum' around the ankle joint.

This raises several questions.
3.a CAN we consider the body on the basis of the "inverted pendulum"? What is the relevance of proximal compensations?
Presuming that the bodies system for maintaining balance is homeostatic is it reasonably to suppose that this system will take steps via other mechanisms to maintain the original (pre stimulus) posture.

3.b The concept of "whole body sway" seems based fairly heavily on the concept of the subject standing still. Presuming the average person spends a good proportion of their weight bearing time walking and a good portion of THAT time on one leg, what are the implications for this mechanism in terms of saggital plane progression, planterflexion moments during mid stance, increased ff loading, FnHL etc.

4.
The really striking thing about stimulation, any stimulation, is that it has its maximum effect immediatly then a declining effect thereafter. This is a fairly universal law. Is there any data based on a similar study which stretches the same experiment over hours or days? Is it reasonable to suppose that the effect will dininish with time as the body becomes accustomed to it (the pharmaceutical challenge).

Like i say, i'll give this rather interesting paper a proper read when i get time. There's 4 questions there just to get us started though.

Kind regards
Robert

[rothbart]

Dear Robert,

I was just notified that I need to make a final proof reading of my paper due for publication in May. Unfortunately, this, combined with a very demanding practice, limits my time available for this discussion. However, below I have addressed your preliminary comments. I should be able to continue this thread in early May.

(1) I have not seen any recent studies comparing tactile to visual input.

(2) Your are correct in their methodology. What is most germaine when looking at Proprioceptive Insoles is their work on plantar stimulation. Proprioceptive stimulation can be in the form of increased tactile (pressure) or vibratory.

(3) This paper evaluated posture by looking at Body Sway Patterns, both sagittally (front to back) and frontally (side to side). Many computer programs use the Body Sway Pattern to judge whether the posture is improving or not (high Sway values, poorer postural stability). Personally, I prefer computerized postural analysis (more visual and intuitive).

(4) I am not sure that the “inverted pendulum” hypothesis works here because we are dealing both with Ascending and Descending Patterns. Although this paper only deals with Ascending patterns, in the clinical arena both are very important.

(5) The body seems to maintain balance (erect posture and minimal sway patterns) based on information coming from the feet and other systems (e.g., eyes and bite)

(6) You comment on whole body sway in a standing still position is “right on” (in my opinion). That is why I prefer computerized postural analysis vs. Body Sway Measurements. However, many research facilities are using BSM as their gold standard.

(7) Regarding the immediate impact of stimulation, diminishing in time – I can only answer that question based on my personal experience. I have found an “engramming” affect that occurs over time. That is, the body requires less stimulation as the Cerebellum is being reprogrammed (theory regarding the reprogramming). It is not that the stimulation diminishes over time, rather, the body no longer needs the same signal strength and if the signal is not reduced, the postural can deteriorate.

We can go deeper into this discussion this May.

Prof B