Dance Anatomy & Kinesiology

82 Dance Anatomy and Kinesiology

Individual Muscles of the Spine

Anterior Muscles of the Spine

The anterior muscles of the spine include various muscles that primarily act on the head and neck

(sternocleidomastoid, three scaleni, prevertebral group), the abdominal muscles, and the iliopsoas. The

abdominal muscles are composed of the paired rectus abdominis, external oblique, internal oblique,

and transverse abdominis. The iliopsoas crosses the hip joint, as well as the spine, and only its func-

tion relative to the spine will be addressed in this chapter.

FIGURE 3.12 The rectus abdominis (anterior view).

Attachments and Primary Actions of Rectus Abdominis

Muscle Inferior attachment(s) Superior attachment(s) Primary action(s)

Rectus abdominis

(REK-tus ab-DOM-i-nis)

Crest of pubis of pelvis, pubic

symphysis

Cartilages of ribs 5-7 Spinal flexion

Spinal lateral flexion (same)

Rectus Abdominis

As its name suggests, the rectus abdominis (rectus,

straight + abdom, abdomen) runs up and down, verti-

cally, in the central portion of the abdomen as seen

in figure 3.12. The rectus abdominis is a relatively

narrow muscle but prominent, and the right and left

recti are separated by a tendinous band called the

linea alba (linea, line + alba, white). The muscle fibers

are parallel in arrangement and are crossed by three

approximately horizontal fibrous bands termed tendi-

nous inscriptions, giving rise to the term “six pack”

used to describe highly developed abdominal muscles.

The rectus abdominis is located superficially and is

encased within a sheath formed by the aponeuroses

of the other abdominal muscles as seen in figure

3.21C. The primary action of the rectus abdominis is

spinal flexion, and the rectus abdominis is considered

the most powerful flexor of the spine. This action of

the rectus is used when one curls the torso up from

a supine position in floor work or performs “contrac-

tions” of the torso in modern or jazz dance. When one

side of the rectus abdominis contracts alone (unilateral contraction), the rectus abdominis can also

assist with spinal lateral flexion to the same side. Posturally, the rectus can also work to pull downward

on the rib cage, depressing the lower ribs and preventing “rib leading,” or to pull upward on the pubic

bone, creating a tucked position of the pelvis (posterior pelvic tilt).

Palpation: Lying on your back with your knees bent and feet flat on the floor, curl up so that your

head and shoulders rise off the floor. The rectus abdominis can be palpated just to the sides of the

midline of the abdomen running from the bottom of the sternum (xiphoid process) to the pubic bone

(symphysis pubis). Also, run your fingertips along the midline of the abdomen. Dancers who have

borne children may occasionally find a crevice between the paired recti abdominis. This separation in

the connective tissue—termed diastasis recti—can occur from the extreme stresses associated with

pregnancy and labor.