Dance Anatomy & Kinesiology

84 Dance Anatomy and Kinesiology

abdominal area laterally toward the iliac crest and

has been shown to demonstrate greater activity in

rotation than the external oblique (Ng et al., 2002).

In contrast, the external oblique has been shown to

exhibit greater activity in lateral flexion than the inter-

nal oblique. Bilateral contraction of the right and left

internal obliques can produce spinal or trunk flexion

and movements like those of the rectus abdominis.

Similar to the external obliques, the internal obliques

can also help flatten the abdominal wall, pull the lower

rib cage down, posteriorly tilt the pelvis, and maintain

spinal stability.

Palpation: Because the obliques and transverse

abdominis are thin layers of muscle running just

superficial or deep to one another, their individual

actions cannot be well differentiated. However, when

one performs the curl-up with rotation to the left (just

described for palpating the external oblique), the ten-

sion palpated on the left side of the abdomen, just

medial to the front of the crest of the pelvis, is in part

due to contraction of the left internal oblique. FIGURE 3.14 The internal oblique abdominal muscle

(lateral view).

Attachments and Primary Actions of Transverse Abdominis

Muscle Lateral attachment(s) Medial attachment(s) Primary action(s)

Transversus abdominis

(trans-VER-sus ab-DOM-i-nis)

Thoracolumbar fascia,

anterior 3/4 of iliac crest,

lateral inguinal ligament, ribs

7-12 (costal cartilages)

Linea alba, pubis Constriction of abdominal

wall and contents

Assists with spinal

stabilization

Transverse Abdominis

(Transversus Abdominis)

As its name suggests, the transverse abdominis (L.

trans, across + versus, to turn + abdom, abdomen)

runs across the abdominal area in an approximately

horizontal manner (figure 3.15). It forms the deepest

layer of the abdominal muscles, lying just beneath

the internal oblique muscles. Similar to the internal

and external obliques, it is a flat muscle, and its

muscular fibers are primarily situated at the sides of

the abdomen. The anterior aponeuroses of the trans-

verse abdominis fuse with the anterior aponeuroses

of the internal and external oblique muscles to form

a single tendon (linea alba) that splits centrally to

form a sheath, in which the rectus abdominis runs

vertically.

In contrast to the other abdominal muscles, the

transverse abdominis is considered primarily a

postural muscle and a muscle of respiration. With

its horizontally directed fibers, it is not capable of

producing spinal flexion. Instead, when its muscle

FIGURE 3.15 The transverse abdominis (anterolat-

eral view).