Oblique Muscle Anatomy

Oblique Muscles

The oblique muscles are 2 muscles:

  • External Oblique
  • Internal Oblique

Internal Oblique Muscle

Internal Oblique

Origin: Lumbar fascia, anterior two-thirds of the iliac crest, and the lateral two-thirds of the inguinal ligament
Insertion: Costal margin, aponeurosis of the rectus sheath, conjoined tendon to the pubic crest and pectineal line, 10-12 rib
Actions: Lateral flexion and rotation of the spine
Innervation: Ventral primary rami of T7 to T12; conjoined tendon supplied by L1
Blood Supply: Branches from the musculophrenic artery, the lower two or three posterior intercostal arteries, the subcostal artery and branches from the superficial epigastric artery

Primary Actions of the Internal Oblique

1. Lateral flexion of the thoracic spine when acting unilaterally

  Agonists: Muscles located on the same side of movement

  • Iliocostalis Cervicis
  • Iliocostalis Thoracis
  • Iliocostalis Lumborum
  • Longissimus Cervicis
  • Longissimus Thoracis
  • External Oblique

  Antagonists: Muscles located on the contralateral side of movement

  • Iliocostalis Cervicis
  • Iliocostalis Thoracis
  • Iliocostalis Lumborum
  • Longissimus Cervicis
  • Longissimus Thoracis
  • External Oblique

Note: Semispinalis cervicis, semispinalis thoracis, and the intertransversarii assist with lateral flexion of the thoracic spine.

2. Lateral flexion of the lumbar spine when acting unilaterally

Agonists: Muscles located on the same side of movement

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Psoas major
  • External oblique

Antagonists: Same muscles on contralateral side

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Psoas major
  • External oblique

Note: The intertransversarii assist with lateral flexion of the lumbar spine.

3. Ipsilateral rotation of the trunk when acting unilaterally

Agonists: None

Secondary Actions of the Internal Oblique

  1. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists:

  • Rectus abdominis

  Antagonists:

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Spinalis thoracis
  • Semispinalis cervicis
  • Semispinalis thoracis

Note: External oblique and psoas major assist with flexion of the thoracic spine.

2. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists:

  • Rectus abdominis

  Antagonists:

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Spinalis thoracis

Note: External oblique and psoas major assist with flexion of the lumbar spine.

3. Assists with forced expiration

Agonists:

  • Serratus posterior inferior
  • Transversus abdominis

  Antagonists: 

  • Serratus posterior superior
  • Levatores costarum breves
  • Levatores costarum longi

Note: Rectus abdominis and external oblique assist with forced expiration.

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External Oblique Muscle

External Oblique Muscle

Origin: Angle of the 9th rib, blending with serratus anterior and from the angles of the 10th, 11th, and 12th ribs, blending with latissimus dorsi.
Insertion: Outer anterior half of the iliac crest, the inguinal ligament, the pubic tubercle and crest, and the aponeurosis of the anterior rectus sheath.
Actions: Lateral flexion and rotation of the spine
Innervation: Ventral primary rami of T7 to T12; conjoined tendon supplied by L1
Blood Supply: Branches from the musculophrenic artery, the lower two or three posterior intercostal arteries, the subcostal artery and branches from the superficial epigastric artery

Primary Action of the External Oblique Muscle

1. Lateral flexion of the thoracic spine when acting unilaterally

  Agonists: Muscles located on the same side of movement

  • Iliocostalis Cervicis
  • Iliocostalis Thoracis
  • Iliocostalis Lumborum
  • Longissimus Cervicis
  • Longissimus Thoracis
  • External Oblique

  Antagonists: Muscles located on the contralateral side of movement

  • Iliocostalis Cervicis
  • Iliocostalis Thoracis
  • Iliocostalis Lumborum
  • Longissimus Cervicis
  • Longissimus Thoracis
  • External Oblique

Note: Semispinalis cervicis, semispinalis thoracis, and the intertransversarii assist with lateral flexion of the thoracic spine.

2. Contralateral rotation of the trunk when acting unilaterally

Agonists: Muscles located on the same side of movement

  • Semispinalis cervicis
  • Semispinalis thoracis
  • Multifidus

Antagonists: Same muscles on contralateral side

  • Semispinalis cervicis
  • Semispinalis thoracis
  • Multifidus

Note: The rotatores assist with contralateral rotation of the trunk.

3.Lateral flexion of the lumbar spine when acting unilaterally

Agonists: Muscles on the same side

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Psoas major
  • Quadratus lumborum
  • Internal oblique

Antagonists: Same muscles on contralateral side

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Psoas major
  • Quadratus lumborum
  • Internal oblique

The intertransversarii assist with lateral flexion of the lumbar spine.

Secondary Action of the External Oblique:

1. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists:

  • Rectus abdominis

  Antagonists:

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Spinalis thoracis
  • Semispinalis cervicis
  • Semispinalis thoracis

Note: Internal oblique and psoas major assist with flexion of the thoracic spine.

2. Assists with flexion of the lumbar spine when acting bilaterally

  Agonists:

  • Rectus abdominis

  Antagonists:

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Spinalis thoracis

Note: Internal oblique and psoas major assist with flexion of the lumbar spine.

3. Assists with forced expiration

Agonists:

  • Serratus posterior inferior
  • Transversus abdominis

  Antagonists: 

  • Serratus posterior superior
  • Levatores costarum breves
  • Levatores costarum longi

Note: Rectus abdominis and external oblique assist with forced expiration.

4. Supports the abdominal wall
Agonists:

  • Rectus abdominis
  • Transversus abdominis
  • Internal oblique

Antagonists: None

The oblique muscles contributes to pain in the  abdomen and groin.

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