Human Movement Science & Functional Anatomy of the:

Internal Obliques

by Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS

 

 

Internal Obliques:

 

  • Origin: Inner surface of ribs 6-12 - interdigitating with the diaphragm, deep layers of the thoracolumbar fascia, anterior 3/4 of the internal lip, 2/3 or the intermediate line, and portion of the iliac crest near the anterior superior spine, and the inguinal ligament.
  • Insertion:  The crest of the pubis, medial part of the pectineal line, linea alba by means of an aponeurosis, medial border of 10 through 12th rib.
    • This internal obliques lay between the external obliques superficially, and the transverse abdominus and peritoneum deep to it.  The fascia of the internal obliques invests with the external oblique to run superficially as the rectus sheath into the linea alba.  It is difficult to differentiate the fibers of the internal obliques, whose fibers run from lateral/inferior to medial/superior, from those of the external obliques and transverse abdominis during palpation.
  • Nerve: segmentally innervated from T7 - T12, L1.
  • Action:
    • Ipsilateral rotator of the spine
      • Note: this must occur in synergy with the contralateral external oblique (a contralateral rotator).
    • Posterior pelvic tilt (this may contribute to sacral nutation).
    • Unilaterally the internal oblique may contribute to lateral flexion.
    • By pulling the ribcage inferior and compressing the abdominal contents this muscle aids in forceful respiration.
        Note: some text differentiate fibers of the internal obliques and state the lower anterior fibers of the internal obliques have an action more closely resembling that of the transverse abdominis (compression and support of the abdominal viscera) (11).  Although the fiber direction is similar research on muscle recruitment strategies show this muscle to have a similar faring rate and sequence as the rectus abdominis and external obliques (13).

     

 

Integrated Function:

  • Stabilization: Stabilization of the lumbar spine, thorax, and pubic symphysis, and potentially the sacroiliac joint by way of attachment to the thoracolumbar fascia.
  • Eccentrically Decelerates:
    • Eccentric deceleration of contralateral rotation of the spine.
      • This has been referred to as "anti-rotation" and may be the most important function of this musculature. The ability to decelerate and stabilize the spine against forces that twist us is paramount to preventing injury.
    • Eccentric deceleration of extension of the spine.
    • Eccentric deceleration of contralateral flexion of the spine
    • Eccentric deceleration of pelvic anterior tilt, also contributing to deceleration of lumbosacral extension and sacroiliac counter-nutation.
      • This function is of particular importance in preventing hyper-extension and excessive reduction of the neural foramina.
  • Synergists:
    • The internal obliques assist in spine rotation with a co-contraction of the contralateral external oblique. Without this co-contraction the internal oblique would produce lateral flexion, and/or pull the rectus abdominis and linea alba laterally. The external obliques have a more advantageous fiber direction and likely a larger cross-sectional area, but this necessary synergy between internal and external obliques resul

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