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self-contained tensegrity. We term this point of view
'tension-dependent spectrum' - the body operating
through different mechanical systems in different situa-
tions and in different parts of the body.
A herniated disc is surely the result of trying to use
the spine as a continuous compression structure, con-
trary to its design. On the other hand, a long jumper
landing at the far end of his leap relies momentarily but
definitively on the compressive resistance of all the leg
bones and cartilages taken together. (Though even in
this case, where the bones of the leg could be thought
of as a 'stack of bricks', the compressive force is distrib-
uted through the collagen network of the bones, and out
into the soft tissues of the entire body in 'tensegrity'
fashion.) In daily activities, the body employs a spec-
trum of structural models from tensegrity to more com-
pression-based modeling. 10 2
Looking at some models that fill in the range from
the pure compression of a stack of blocks to the self-
contained tensegrity of Figure 1.59, a sailboat provides
one of several 'middle ground' structures (Fig. 1.61). At
anchor, the mast will stand on its own, but when you
'see the sails conceive, and grow big-bellied with the
wanton wind', the fully loaded mast must be further
supported by the tensional shrouds and stays or it will
snap. By means of the tensile wires, forces are distrib-
uted around the boat, and the mast can be thinner and
lighter than it otherwise would be. Our spine is simi-
larly constructed to depend on the balance of tension
member 'stays' (the erector spinae, longissimus specifi-
cally) around it to reduce the necessity for extra size and
weight in the spinal structure, especially in the lumbars
(Fig. 1.62).
The structures of Frei Otto, beautiful membranous
biomimetic architecture that relies on tensional princi-
ples but is not pure autonomous tensegrity (because it is
anchored to and relies on its connections to the ground),
can be seen in Denver's new airport, or at www.freiotto.
com (Fig. 1.63). Here we can see, especially with the cable
and membrane structures that characterize the Munich
Olympiazentrum, a further exploration of a tension-
compression balance which leans strongly toward reli-
Fig. 1.62 In a similar way, the erectors, specifically the
longissimus, act as our 'stays' in the spine, allowing the spine to
be smaller than it would otherwise have to be if it were a
continuous compression structure. The iliocostalis is constructed
and acts like the mast below (Image provided courtesy of Primal
Fig. 1.61 A sailboat is not strictly a tensegrity structure, but the
structural integrity still depends somewhat on the tension members
- the shrouds, stays, halyards, and sheets that take some of the
excess strain so that the mast can be smaller than it otherwise
would have to be.
Fig. 1.63 This mast of Frei Otto relies even more heavily on
tension for its integrity. The core is flexible, and would fall over
without the cables to hold it up. By adjusting the cables and then
securing them, this mast can be made a solid support in any
number of different positions.
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