The Spine 93FIGURE 3.22 Posterior view of primary muscles acting on the spine. (A) Muscles and attachments, (B) deep posterior
spinal group, (C) line of pull and actions.
Ideal Standing Postural Alignment
Although controversial, this text will consider ideal
posture to encompass a balance of these sagittal
curves and a positioning of joints so that the body’s
line of gravity is located in the median plane and runs
in front of the thoracic vertebrae and just anterior to
or through S2 as seen in figure 3.23A (Hamilton and
Luttgens, 2002; Levangie and Norkin, 2001). This
gravity line would ideally pass through or close to thecenters of key weightbearing joints so that undue joint
stress is avoided and minimal muscular contraction is
required to maintain the desired positioning.
More specifically, positioning of the line of gravity
allows much of the necessary support for the spine
to be provided by intervertebral disc pressures and
constraints offered by ligaments, fascia, and capsules
of the facet joints (Caillet, 1996). Slight additional
active support is often provided by low levels of activ-
ity of the spinal extensors (particularly the thoracic