Healthcare and Medicine Reference
In-Depth Information
Fig. 1.52 A complex model shows how the pelvis, for instance,
could be made up of smaller pre-stressed tensegrity units. (Photo
and concept courtesy of Tom Flemons, www.intensiondesigns.
com.)
Tensional forces naturally transmit themselves over
the shortest distance between two points, so the elastic
members of tensegrity structures are precisely posi-
tioned to best withstand applied stress. For this reason
tensegrity structures offer a maximum amount of
strength for any given amount of material. 9 0 Addition-
ally, either the compression units or the tensile members
in tensegrity structures can themselves be constructed
in a tensegrity manner, further increasing the efficiency
and 'performance/kilo' ratio (Fig. 1.52). These nested
hierarchies can be seen from the smallest to the largest
structures in our universe. 92,9 3
Now, our commonly held and widely taught impres-
sion is that the skeleton is a continuous compression
structure, like the brick wall: that the weight of the head
rests on the 7th cervical, the head and thorax rest on the
5th lumbar, and so on down to the feet, which must bear
the whole weight of the body and transmit that weight
to the earth (Fig. 1.53). This concept is reinforced in the
classroom skeleton, even though such a representation
must be reinforced with rigid hardware and hung from
an accompanying stand. According to the common
concept, the muscles (read: myofascia) hang from this
structurally stable skeleton and move it around, the way
the cables move a crane (Fig. 1.54, compare to Fig. 1.50B).
This mechanical model lends itself to the traditional
picture of the actions of individual muscles on the bones:
the muscle draws the two insertions closer to each other
and thus affects the skeletal superstructure, depending
on the physics.
In this traditional mechanical model, forces are
localized. If a tree falls on one corner of your average
rectangular building, that corner will collapse, perhaps
without damaging the rest of the structure. Most modern
manipulative therapy works out from this idea: if a
part is injured, it is because localized forces have
overcome local tissues, and local relief and repair are
necessary.
Fig. 1.53 Given the ease of building and simplicity of continuous
compression structures, and given how many of them we make to
live and work in, it is not surprising that the principles of tensegrity
remained obscured for so long. This figure shows a familiar
continuous compression model of the body - the head resting on
C7, the upper body resting on L5, and the entire body resting like
a stack of bricks on the feet. (Redrawn from Cailliet R. FA Davis;
1997.)
Fig. 1.54 The erector spinae muscles can be seen as working like
a crane, holding the head aloft and pulling the spine into its
primary and secondary curves. The actual biomechanics seem to
be more synergetic, less isolated, requiring a more complex model
than the traditional kinesiological analysis. (Reproduced with kind
permission from Grundy 1982.)
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