The Spine 81around one axis with motion around a different axis
is termed coupling (Levangie and Norkin, 2001).
Skilled dancers often develop a complex array of
muscle activation patterns to limit some of this cou-
pling when the dance aesthetics require the look of
motion of the spine as a whole in a single plane. For
example, some floor work in modern dance utilizes
rotation with a “long and lifted spine,” with minimal
accompanying visible lateral shift or side-bending of
portions of the spine.
Muscles
In addition to the many strong ligaments and joint
capsules of the vertebral column, many muscles act
on the spine. These muscles range from small slips
vital for local stabilization to large muscles capable
of generating large forces. Given the tremendous
number of joints and the complexity of the spine,
heightened by the presence of the normal sagittal
curvatures, these muscles are vital for moving the
spine, stabilizing the spine, and preventing injuries
that occur so readily in this region of the body.
Description and Functions of Individual Muscles of the Spine.
The back region contains approximately 200 muscles
(Rasch and Burke, 1978), including muscles for res-
piration, moving the upper extremity, and moving
the vertebral column. This text will simplify coverage
to key muscles for stabilization and movements of
the spine, and it will exclude many of the muscles
that move the neck and head. The location of these
selected spinal muscles has a logical relationship
to their actions, with anterior muscles other than
the iliopsoas producing spinal flexion, posterior
muscles producing spinal extension, and lateral
muscles producing lateral flexion. Most anterior
and posterior muscles also have secondary actions
of spinal rotation and lateral flexion. Many of these
muscles attach onto the pelvis and thorax rather than
the vertebrae themselves, making their influence on
the spine indirect. (See Individual Muscles of the
Spine, pp. 82-93.)
Ideal Spinal Alignment and Common Deviations
When one looks from the side, the spine is not a
straight column but has four curves as seen in figure
3.1B. The cervical and lumbar curvatures are convex
anteriorly, and the thoracic and sacrococcygeal
curvatures are convex posteriorly. The thoracic and
sacral curvatures are primary curvatures that develop
during the fetal period and are present at birth (Hall-
Craggs, 1985) as seen in figure 3.1A. The thoracic
curve is due primarily to the wedged shape of the
vertebrae in this region. In contrast, the cervical and
lumbar curvatures do not fully develop until after
birth and thus are termed secondary curvatures.
The cervical curve has been conjectured to develop
in response to the pull of the neck extensors as the
infant begins lifting the head up with sitting and
crawling. The lumbar curve is further formed when
the child starts standing and walking. When the child
stands, the tightness of the iliofemoral ligament and
hip flexors (see chapter 4) will tend to tilt the top
of the pelvis anteriorly, and the lumbar spine must
be extended to keep the torso upright. Unlike the
other curves, the lumbar curve also tends to increase
during the growth years; an approximate 10° increase
occurs between the ages of 7 and 17 (Hall, 1999).
The lumbar curve is unique to the human species
and is believed to be a specialized adaptation to
upright stance and gait (Napier, 1967). The lumbar
and sacrococcygeal curvatures tend to be more pro-
nounced in females than in males. In contrast, the
thoracic curvature tends to be higher in males than
females prior to age 40, and then similar, or in some
cases much greater, in females in later years (White
III and Panjabi, 1978).
When these sagittal curves are of normal mag-
nitude, their balanced presence contributes to the
springlike characteristics of the spine and allows it
to withstand greater forces and move more freely
than if it were a straight column. However, in some
instances, one or more of these curves is excessive,
disrupting this balance and placing undue stress on
some segments of the spine. Exaggerations of the
normal curves in the sagittal plane include cervi-
cal lordosis, kyphosis, and lumbar lordosis, while
a decrease in the lumbar curve is termed flat back
(figure 3.23, p. 94). An abnormal curve occurring
primarily in the frontal plane is termed scoliosis.
Milder forms of these alignment problems may
relate to muscular imbalances and habitual move-
ment patterns, but it is also important to realize that
these alignment conditions may be related to more
serious underlying pathology and may have a strong
genetic basis or psychological basis. Therefore, it is
important that the dancer procure a good medical
evaluation if any of these conditions are accompa-
nied by pain, appear to be progressing, or are severe
in magnitude.
(Text continues on p. 93.)