External Oblique

The external oblique is a paired muscle located on the anterolateral trunk and is superficial to the internal oblique and lateral to the rectus abdominis.

The muscle fibers run at an oblique angle from the lateral ribs anteriorly and inferiorly to the ilium, inguinal ligament, and linea alba. The origin of the external oblique interdigitates with the costal attachments of the serratus anterior and forms a distinct zigzag line on the lateral trunk, just below the armpit.

The external oblique is a thick, strong, prime mover muscle that works with the internal oblique and transverse abdominis to compress and protect the abdominal contents during forced exhalation. During movement, the right and left sides of the external and internal obliques work together in various combinations. Forward flexion is achieved when all four muscles (right and left external obliques and right and left internal obliques) are activated. Lateral flexion occurs with activation of the external and internal obliques on the same side. For rotation, the right external oblique teams up with the left internal oblique to turn the trunk to the left.

Conversely, the left external oblique works with the right internal oblique to turn the trunk to the right. As these motions occur, the transversospinalis muscles, located much deeper and attaching to the vertebral column, maintain vertebral alignment. The external obliques are active during large, powerful motions like swinging an axe, throwing overhand, or pushing with one or both hands.

Both excessive and inadequate activation of the external obliques can be problematic. If the deeper stabilizer muscles are underutilized or atrophied, the external obliques may become hypertonic and produce global "bracing" of the trunk during movement.

This often perpetuates vertebral stiffness and may lead to more serious chronic issues, such as intervertebral disk degeneration. Poor activation and associated muscle atrophy of the external obliques exacerbates postural deviations like anterior pelvic tilt and contributes to an overall lack of core strength.

A Deeper Dive—Palpating the External Oblique

Positioning: client supine.

1. Standing at the client's side, face the abdomen and locate the inferior edge of the anterolateral rib cage with the palm of your hand.
2. Slide your hand inferiorly into the space between the iliac crest and inferior edge of the rib cage.
3. Locate the sloping fibers of the external oblique as it angles anteriorly and inferiorly from the lateral rib cage toward the linea alba.
4. The client gently curls the trunk, lifting the shoulder toward the opposite hip to ensure proper location.

Client Homework

Bilateral stretch: extension

1. Stand or sit with good upright alignment.
2. Place both palms on your low back, just above the buttocks.
3. Begin by looking up at the ceiling, then, as you exhale, gently curl your spine back, opening up your chest and abdomen.

Unilateral stretch: lateral flexion

1. Stand or sit with good upright alignment.
2. Elongate your spine as you take in a deep breath.
3. As you exhale, curl your spine to one side as you reach your shoulder toward your hip.
4. Take several breaths as you relax and lengthen the muscles on the opposite side.
5. Return to upright position and repeat on the other side.

Editor's note: The Client Homework element in Functional Anatomy is intended as a take-home resource for clients experiencing issues with the profiled muscle. The stretches identified in Functional Anatomy should not be performed within massage sessions or progressed by massage therapists, in order to comply with state laws and maintain scope of practice.