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42 m a s s a g e & b o d y w o r k n o v e m b e r / d e c e m b e r 2 0 2 0 FUNCTIONAL ANATOMY education 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. Christy Cael is a licensed massage therapist and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (New York: Jones & Bartlett Learning, 2010; www.jblearning.com). Contact her at christy_cael@hotmail.com. External Oblique By Christy Cael EXTERNAL OBLIQUE Attachments • Origin: External surfaces of ribs 5–12 • Insertion: Anterior half of iliac crest, inguinal ligament, and linea alba Actions • Flexes spine (bilateral action) • Laterally flexes spine to same side (unilateral action) • Rotates spine to opposite side (unilateral action) • Compresses and supports abdominal organs Innervation • Intercostal nerves T7–11 (upper 2 /3) • Subcostal nerve T12 (upper 2 /3) • Iliohypogastric nerve L1 (lower 1 /3)