108 Dance Anatomy and Kinesiology
intra-abdominal pressure generation, and its role is
probably more that of control of movements of the
spine. Hence, abdominal strengthening exercises
should be selected and cued to emphasize strengthen-
ing the transverse and oblique abdominal muscles.Psoas Paradox
Although the iliopsoas is primarily considered a hip
flexor, it can also produce movements of the spine
that are influenced by the position of the body. When
the spine is in a flexed position, the line of pull of the
iliopsoas is generally anterior to the axis of rotation
of the lumbar intervertebral joints, and it will tend to
produce flexion of the lumbar spine (Levangie and
Norkin, 2001). The iliopsoas acts in this function
during rope climbing, Graham contractions, and
various dance warm-ups performed on the floor that
involve swinging the leg forward (hip flexion) with
the lumbar spine in flexion. However, in most cases
(such as with normal standing) when the lumbar
spine is in extension, the line of pull of many of the
fibers of the iliopsoas runs posterior to the lumbar
intervertebral joints and tends to produce extension
(hyperextension) of the lumbar spine. This appar-
ent role reversal from its usual tendency to produce
extension of the lumbar spine to being a flexor of
the lumbar spine is termed the psoas paradox. This
general tendency to produce lumbar hyperexten-
sion may be desirable in some instances, such as to
help maintain the lumbar curve with upright stand-
ing. However, there are many other cases, such as
when lifting the gesture leg to the front in dance
or in double-leg lift abdominal exercises, when it is
undesirable, and firm contraction of the abdominal
muscles is required to stabilize the proximal attach-
ments of the iliopsoas and prevent the undesired
anterior pelvic tilt and spinal hyperextension.Muscular Analysis of Fundamental Spinal Movements
In analyzing movements of the spine, it is important
to realize that they are often linked with movements
of the pelvis. This relationship will be discussed in
chapter 4. It is also important to realize that the
segmental structure of the spine allows different
movement capacities in different regions of the spine
and allows one part of the spine to move in one direc-
tion while another part moves in another direction.
However, for purposes of simplicity, it is helpful to
first learn movement of the spine as a whole.To understand what muscles are producing a
given movement of the spine, it is essential to appre-
ciate the role of gravity when standing upright. In this
upright position, the spine is in a potentially precari-
ous position, and if it is moved in any direction “off
center,” gravity will tend to make it fall in that direc-
tion. Often a slight voluntary concentric contraction
is used to initiate movement in a desired direction.
Then gravity becomes the primary mover, and
muscles with actions opposite to the movement pro-
duced by gravity are used to control that movement.
To visualize these movements, it is helpful to think of
the spine as a flexible column with the muscles acting
like guy ropes relative to the spine (Smith, Weiss, and
Lehmkuhl, 1996). When the vertebral column is verti-
cal, little or no tension in the guy ropes is required.
However, when the vertebral column leans off the
vertical, the guy ropes (e.g., muscles) opposite to the
direction in which the spine is leaning must contract
to control or prevent the falling of the spine in that
direction. Muscles of the spine are also often used
together (co-contraction) in a coordinated manner
to create a stable desired position of the spine. A
summary of the muscles capable of producing the
fundamental movements of the spine is provided
in table 3.2, and an illustration of the fundamental
movements of the spine was given in figure 3.11.Spinal Flexion
Spinal flexion is forward bending in the sagittal
plane, tending to bring anterior surfaces of the
vertebrae and trunk together. However, because the
cervical and lumbar regions curve in the direction
of hyperextension (concave posteriorly), flexion of
these regions may represent a decrease in extension
or a flattening of the curve, without actually neces-
sarily producing a position of flexion of the adjacent
vertebrae. It is common in the cervical curve for
flexion to reduce the curve to a straight line; and in
flexible individuals, the lumbar curve may actually
be reversed.
The classic concentric use of the abdominal mus-
cles and other spinal flexors occurs when the spine
flexes or the pelvis posteriorly tilts against gravity or
another external resistance. When gravity offers the
resistance, a supine position of the body allows for
effective resistance. For example, in the isometric
curl-up (see table 3.4B [p. 134]), the spinal flexors
work concentrically on the up-phase to curl the torso.
The rectus abdominis and right and left external and
internal obliques all act together to produce spinal
flexion, while the transverse abdominis ideally aids
with pulling the abdominal wall inward. With slow