The Spine 85fibers contract, the transverse abdominis compresses the abdominal contents. Hence, it is sometimes
referred to as the “corset muscle” because it encloses the abdominal cavity similarly to the way a corset
would. The transverse abdominis is used in such actions as forced expiration, coughing, sneezing,
speech, laughing, straining, and pulling the abdominal wall in toward the spine. Although in the case
of breathing, it appears that the transverse abdominis can be preferentially recruited, the other move-
ments just listed are not effected by the transverse abdominis alone but rather usually also include
contraction of the rectus abdominis to a lesser extent and obliques to a greater extent (De Troyer et
al., 1990; Floyd and Silver, 1950). The transverse abdominis has also been shown to be particularly
important for stabilization of the spine when the arms or legs move and for helping protect the spine
during lifting. In dance, the function of the transverse abdominis of “pulling the abdominal wall inward”
to help produce the aesthetically desired “flat abdomen” is often emphasized.
Palpation: Place your hand flat against your abdomen, with the heel of the hand below the ribs and
above the side of the ilium and the fingers pointing toward the umbilicus. Then, forcibly exhale. Part of
the tension felt under your hand is due to contraction of the transverse abdominis.Attachments and Primary Action of Iliopsoas
Muscle Proximal attachment(s) Distal attachment(s) Primary action(s)
Iliopsoas (il-ee-o-SO-us)
Psoas major
(SO-us)Transverse processes, bodies,
and intervertebral discs of T12-L5Lesser trochanter of femur Hip flexion
Posture (maintenance of
normal lumbar curve)
Iliacus
(il-ee-AK-us)Iliac fossa, crest of ilium, sacrum Lesser trochanter of femur Hip flexionIliopsoas
The iliopsoas—composed of the psoas major and
iliacus—is a powerful flexor of the hip, and this func-
tion will be further discussed in chapter 4. However,
it is important to note that due to its attachment
onto the anterior portion of the bodies, discs, and
transverse processes of the last thoracic vertebra
and entire lumbar spine (T12-L5), the psoas major
(G. psoa, muscles of the loin + great) also can
directly influence the lumbar spine, under most
conditions producing lumbar extension and lateral
flexion during upright standing (see Psoas Paradox
on p. 108 for more information). In contrast, the
iliacus (iliac, relating to the ilium) can indirectly
affect the curvature of the spine through its exten-
sive attachment on the pelvis (figure 3.16), since
pulling the top of the pelvis forward (anterior pelvic
tilt) is accompanied by an increase in lumbar exten-
sion. Hence, the iliopsoas is believed to be a key
for maintaining the normal lumbar curve (Hamilton
and Luttgens, 2002; Michele, 1960) during upright
sitting and standing (Basmajian and DeLuca, 1985; Nachemson, 1966), and bilateral tightness can
contribute to an excessive lumbar curvature (lumbar hyperlordosis), while excess length and weakness
can contribute to an inadequate lumbar curve (flat back posture). Unilateral iliopsoas tightness can
produce a lateral curvature of the spine (functional scoliosis) or slight rotations of the spine or pelvis
commonly seen in dancers.FIGURE 3.16 The iliopsoas (anterior view).