Tuesday, December 11, 2012

The Human "Hybrid" Skeleton

What in the world are you talking about?!  This is the likely question.  The obvious understanding of human anatomy is that we are effectively characterized by an endoskeleton...or "bony structure lies underneath soft tissue" .  Well...although these familiar labels are quite convenient, they are equally simplistic.  My intention is to use this relatively "light" discussion as an introduction to my upcoming (and comparatively "heavy") post on what true posture really is (title yet to be assigned).

The definition of endoskeleton has already been given, and as the cartoon post image demonstrates, creatures with an exoskeleton are characterized by an external skeleton while the soft tissue remains contained within.  If the question were to be asked "are humans endo or exo?", the odds are that 99.9% would say ENDO.  Therefore, am I suggesting that we are EXO?  As with all biological organisms, humans are a mixture of both.

This is an intuitive question, but requires some extensive leaps into evolution and the process by which man moved from water to land...which I will save for another time.  However, it should be understood that because of the realities of entropy, we are engineered in the most efficient manner...therefore there must be an architectural reason for the development of a "hybrid skeleton".  I will follow with a more detailed explanation of what i refer to as a hybrid skeleton, but i wanted to convey a fundamental message beforehand:  the realities of moving within a gravitational field have resulted in an efficient blend of compressional and tensional properties (biotensegral properties) that allow for some of the most fluid and precise movements on the planet.  

The Hybrid skeleton is characterized by an exoskeletal "core" and an endoskeletal "periphery".   The core is defined by the thorax, abdomen, and pelvis...while the periphery are the limbs (including the neck).


The above image illustrates the exoskeletal characteristics of the core.  The thorax is amazingly removed from the vertebral column and, given that the arms interact with the shoulder blade, the entire portion can be removed like a "coat".  Therefore this is essentially the representation of an exoskeleton...the superficial muscles (pectoralis, latissimus dorsi, subscapularis, etc...) essentially serve dynamic function and therefore are excluded from the exoskeleton definition.

Soft visceral core

What remains is demonstrated above...a soft tissue "hydraulic" core that is characterized by the lungs, abdominal and pelvic contents, as well as the fascial "wrapping" that encompasses them.  I will exhance this concept in greater detail in the upcoming postural post, however the visceral core of the body is what provides us with postural competence (or postural ability).  The architectural qualities of the exoskeleton provide the most efficient mechanism to provide compressional (postural) strength under a gravitational field.

Visceral core within thoracic cage and pelvic girdle

Above is a demonstration of the soft tissue core "in situ" within the thorax and pelvis.  This informative image gives tremendous perspective into how the deep visceral core (true core) drives the developmental growth of the pelvis and thorax...and therefore the legs and arms.

Tensional characteristics of the arms
The arms and legs therefore exhibit the endoskeletal characteristics dues to the fact that the tensional properties are required for human locomotion.  Effectively the muscles effect tensional force on top of compressional integrity to facilitate movement...hence the concept of biotensegrity.  A fundamental understanding:  tensional force cannot be generated without a competent compressional component.
This last stement will be the key focus of the "true posture" post to follow.

Again, credit to Richard Paletta for formalizing the visceral core concept with the images within this post.  Further credit goes to the works of Frederick Woods Jones who makes some rather startling comparisons between the human organism and our sea-dwelling creatures.

Stay tuned for what will hopefully be an insightful formalization of an interesting concept of posture...more importantly how it fits onto the complex and comprehensive world of movement disorders.