Internal Oblique
Musculus obliquus internus abdominis
The internal oblique lies just beneath the external oblique, with fibers running perpendicular to it (upward and inward). It flexes and side-bends the trunk and rotates it to the SAME side, so it works as a functional pair with the opposite-side external oblique to produce trunk rotation. Like the external oblique it is trained through rotational and anti-rotation work and contributes strongly to bracing and intra-abdominal pressure during heavy lifts.
- Actions
- Trunk flexion, Lateral trunk flexion (ipsilateral), Ipsilateral trunk rotation, Increases intra-abdominal pressure, Forced expiration
- Origin
- Thoracolumbar fascia, anterior two-thirds of the iliac crest, and lateral half of the inguinal ligament
- Insertion
- Inferior borders of ribs 10-12, linea alba, and pubic crest/pecten pubis (via conjoint tendon)
- Innervation
- Thoracoabdominal nerves (T7-T11), subcostal nerve (T12), iliohypogastric and ilioinguinal nerves (L1)
- Blood supply
- Lower posterior intercostal, subcostal, and deep circumflex iliac arteries
Antagonists Erector Spinae
Exercises (16)
Trains as a primary mover
Assists in