The external oblique is the largest and most superficial lateral abdominal muscle. Its fibres run inferomedially ('hands in pockets' direction), and its aponeurosis forms the anterior wall of the rectus sheath and contributes to the inguinal ligament. The external oblique aponeurosis has a superficial ring (external inguinal ring) that transmits the spermatic cord or round ligament.
| Origin | External surfaces of ribs 5-12 (digitations interleaving with serratus anterior at the upper ribs) |
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| Insertion | Anterior iliac crest, ASIS (via the inguinal ligament from anterior superior iliac spine to pubic tubercle), linea alba (via aponeurosis), and pubic tubercle |
| Nerve Supply | Intercostal nerves T5-T11, subcostal nerve T12 |
| Blood Supply | Lower intercostal and subcostal arteries |
| Actions | Ipsilateral lateral flexion; Contralateral rotation (working with the opposite internal oblique); Bilateral contraction: trunk flexion, abdominal compression, forced expiration |
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External oblique strain from rapid trunk rotation in throwing and racket sports produces lateral abdominal pain. The external oblique aponeurosis contributes to inguinal hernia anatomy — the posterior wall of the inguinal canal is reinforced by the external oblique aponeurosis anteriorly and the conjoint tendon posteriorly.
The external oblique is palpable along the lateral thoracic cage and the flank, becoming firm during resisted trunk rotation to the opposite side.
Trunk rotation overload producing lateral abdominal pain managed conservatively with progressive loading.
