Sunday, April 29, 2012

The "New" Understanding of Anatomy: Pre-Stressed Systems

PRE-STRESSED SYSTEMS: The first installment of the ¨Wheel¨ series is an introduction to a fundamental characteristic of complex biological systems. The very definition of ¨complex¨ indicates that these types of systems are difficult to de-construction and effectively understand...therefore I will present this specific characteristic in a more straight-forward and ¨simplistic¨ way. It is important to realize and understand the fundamental difference between organic and inorganic structures. This statement may seem trivial...of course there is a difference...however, the reality (and experience) shows that this logic goes completely out the window when we examine conventional rehabilitative strategies. Simple mathematical models and equations can successfully be applied to simple (inorganic) structures without any significant concern for error. The inconvenient reality is that these same simple mathematical models (lever classes, axis of rotation, range of motion, etc) are being ¨imported¨ to represent complex organic if they were both the same. This is effectively where the proverbial ¨boat¨ gets missed. Effective rehabilitation strategies hinge on understanding the fundamentals of the organic ¨Superstructure¨...which is a structure that is PRE-STRESSED. Pre-stressed systems are characterized by a built-in tensional component that allows it to respond / adjust to the changing environment and, consequently, the internal forces it generates. This phenomenon is ironically all around us...and can be observed every single day. For example, the earthquake that struck Haiti a couple of years ago left the entire country devastated. It was a large magnitude quake that left the buildings in ruins and rubble. However, a significantly larger quake hit Chile...and even with the larger, taller buildings almost none of them came down. Why? The buildings are built PRE-STRESSED. Therefore, ground force reaction (represented by the earthquake) is efficiently distributed throughout the entire system and permits the building to adjust. How is this applicable to the human body and rehabilitation? Let´s move into some specifics:
A simple wagon wheel is a rigidly made structure that is essentially built for obvious purposes. This is a good example of a non-stressed structure.
When it rolls along the ground, the individual spoke (and the rim in contact with the ground) take absorb the ground force reaction while the other spokes do nothing. In effect, the entire weight of the wheel (and therefore all of the ground-force reaction) goes through a relatively small area. This illustrates the ¨Support comes from the bottom¨ the bottom part of the wheel provides 100% of the support for the movement.

A bicycle wheel, although functionally equivalent to the wagon wheel, is a much more sophisticated and efficient contruction. The spokes of a bicycle wheel are PRE-STRESSED...therefore they have a pre-existing tensional component to them (green arrows).

As the wheel rolls, ground force reaction enters from the bottom, thereby reducing the tension on the bottom spokes...which consequently results in an INCREASE IN TENSIONAL SUPPORT FROM THE UPPER SPOKES. This global response allows the wheel to absorb significantly more force and stress without failing (breaking). The question may arise again: How in the world is this applicable? The body is not a bicycle wheel! Indeed, it is not...but it IS pre-stressed!

As ground-forces are imposed into the system from the bottom, the reaction is the same. The tensional support (tensegral) comes from the top. This is easily observed by placing your fingers between the trochanter and iliac bone and walking a few steps. As you heel strike, you will feel a palpable increase in tension. This is a counter-intuitive reaction and can therefore create some relative confusion. However, a study of pre-stressed systems (as well as a delve into Biotensegrity) will reveal that this is by far the most accurate representation of how complex systems work. Therefore, a radical shift in rehabilitative assessment and evaluation is in order. Traditional ¨proven¨ techniques such as gait analysis do not take this into account...therefore produce very diluted and simplistic strategies. If we take this realization further and quickly examine the sitting position, the Tensegral / Pre-stressed paradigm takes on a much more tangible role.

When seated, support will be derived from the top. As the ground forces are imposed on the pelvis, the entire system will adjust accordingly. In summary, the entire framework of ¨rehabilitation¨ needs to be established based on how the body actually works. The current health care delivery system is geared to address the masses...and therefore needs to be simplified to the most common denominator and provide strategies that fit the majority. However as INDIVIDUAL helath care providers, we need to make a concerned effort to customize our protocols towards strategies based in fundamentals of the human organism. I hope I have been somewhat successful in delivering this important message. Part 2 will continue the exploration into compex systems and attempt to draw links and bridge gaps. Cheers!

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