The Spine 111anatomical position from left lateral flexion would
be termed right lateral flexion, and vice versa.
The classic concentric use of the spinal lateral
flexors occurs when the spine laterally flexes against
gravity or resistance such as in side-ups (see table
3.4K [p. 139]). The quadratus lumborum, oblique
abdominal muscles, and erector spinae are considered
the primary lateral flexors. Note that the external
and internal obliques on the same side of the body
would be working to produce the same motion (e.g.,
when lying on your right side, the left external and
left internal oblique would both produce the desired
left lateral flexion). In some cases, the semispinalis,
deep posterior spinal extensors, rectus abdominis,
and iliopsoas also assist with the movement. Which
muscles contribute to the movement is influenced by
the amount of resistance, speed of the motion, and
specific positioning of the trunk. For example, when
pure lateral flexion occurs there appears to be little
action of the rectus abdominis, but when it is com-
bined with slight flexion of the torso, the rectus and
oblique co-contract to help produce the motion.
During upright standing, the spinal lateral flexors
work whenever the torso is bent to the side. This
motion is commonly used in modern and jazz move-
ments and second-position floor or barre stretches in
which the torso is bending or reaching to the side as
seen in figure 3.34. In the pictured movement, the
right lateral flexors initiate the movement. Then
once the spine is off center, the left lateral flexors
would primarily work to control the motion eccentri-
cally, motivated primarily by gravity once the spine is
off center. As with side-lying movements, the specific
contribution of the spinal lateral flexors appears to
be affected by position of the trunk. However, the
oblique muscles appear to be particularly impor-
tant, with the contribution of the spinal extensors
more variable (Basmajian and DeLuca, 1985). For
example, one study found greater activity in theFIGURE 3.33 Sample dance movement showing spinal
extension.
© Angela Sterling Photography. Pacific Northwest Ballet dancer Melanie Skinner.FIGURE 3.34 Sample dance movement showing spinal lateral
flexion.
Photo courtesy of Bill Evans. Photographer: Jack Mitchell. Dancer: Bill Evans in “Five Songs.”