Kenneth Snelson
X-Column, 1959
aluminum and bead chain
35.5 x 6 x 6 in
90 x 15 x 15 cm

The engineering specifications for our spines are demanding:

  • Capacity to support a load potentially over 100 lbs. for over 80 years.
  • Twist 180° in each direction (360° total rotation)
  • Bend 90° to each side (180° total bend) and flexion > 90°.
  • Manage shock loads many times greater than the carrying load.
  • Function as a conduit for the nervous system (the closer the spinal cord is to the center of rotation the shorter it can be).

These demands are successfully incorporated into a Spine that evolved to function radically differently. The most ancient quadrupeds in our lineage slid along the ground, using their four legs to push and pull themselves along (consider Alligators). As the descendants of these animals acquired proficiency in managing their mass, they attained the strength and speed that we observe in many Mammals. As our ancestors evolved other uses for their forelegs more demands for weight-bearing were placed on their Pelvis and Spines, leading eventually to our bipedal gait and use of our forelegs as an evolutionarily distinct divergence discussed here as the Manipulation Core.

In four-legged Mammals, the body “hangs” off of a horizontal spine. To implement this, the spine is in tension as much as it is in compression. This is easiest to see in the position of the head forward of the forelegs, which must be “held-up” in tension against a compressional resistance. The vigorous and fluid movements we observe in Mammals require a dynamic interplay of tensional and compressional forces. This interplay is discussed in the section on Biotensegrity. When our ancestors came to stack their weight over their spines these tensional and compressional dynamics facilitated the development of a much lighter and more graceful spine than would be required if it was engineered based purely on compressional loading. The Kenneth Snelson sculpture “X-Column”, shown above, captures this interplay on compressional and tensional forces in a vertical structure. It is challenging for this writer to imagine how a purely compressional structure could embody the range of functions listed at the beginning of this section.

This perspective is important therapeutically. When the spine is understood as a purely compressional (static) structure, dysfunction is approached therapeutically by adding bracing (from Back Braces to surgically implanting rods). When the Spine is understood as a distributed network of compressional and tensional forces localized issues at a specific Spinal Segment are approached by working with those segment’s relationships to the wholistic structure, more directly than with the segment itself. It is even possible that spinal issues may be resolved by working with the feet or the head. Without addressing these relationships, bracing a specific spinal segment transfers the imbalance to neighboring segments, thereby amplifying the issue as those segments shoulder the functional role of the braced segment. Additionally, the tensional attributes are not static as represented by the sculpture “X-Column” illustrated above, but rather dynamic and adaptive, managed by the cognitive mechanisms that coevolved with the emergent structural complexity. It is therefore only possible to approach the Spine therapeutically by assessing the functionality of the associated neuromotor attributes (how we stand and move). These papers elucidate aspects of these functional attributes as they relate to the Spine:

As upright animals, the tensioning mechanism that maintains our erectness is quite sophisticated, extending from the soles of our feet up our backs to the base of our skulls. We describe this mechanism as Postural Extension which is discussed in some detail here:

Additionally, the section on Movement explores spinal function in the broader context of how we move:
and the section on the Sensory/Processing Core explores the cognitive aspect of this tensioning capability as an aspect of our global functionality:

Here are specific discussions on ways to take care of our Spines:


A post on the functional mechanism the Spine supports:

A post on the dynamics of Stance:

A discussion on our Locomotive Core

A discussion on our core structural attributes:

A discussion on the models for our species presented on this website