Human Movement Science & Functional Anatomy of the:
by Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS
- 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.
- 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).
- Ipsilateral rotator of the spine
- 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.
- Eccentric deceleration of contralateral rotation of the spine.
- 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 results in the “obliques” (both internal and external) being labeled as the primary rotators of the spine in most texts.
- The internal obliques are synergists to trunk flexion, although, likely third in ability to produce force behind the external obliques and the prime mover, the rectus abdominis.
- The internal obliques are synergists for lateral flexion of the spine, again likely third in ability to produce force behind the external oblique, and prime mover quadratus lumborum.
- The internal obliques are an important stabilizer when the body resists a significant external load. The use of global trunk musculature to stabilize the spine is often termed “bracing” and includes isometric contractions from all trunk musculature including the internal obliques. There is some debate on whether this muscle is truly a global muscle or part of the intrinsic stabilization subsystem. The work by Richardson et. al seems to point toward a recruitment pattern that links these muscles with the external obliques and rectus abdominis (see reference “13” below and the article 3 Classic Studies in Core Muscle Recruitment). However, some studies show that TVA activation is often paired with an increase in internal oblique activity (13, 14). This is not surprising as the fiber arrangement of these two muscle is very similar, the most lateral aspects of the internal obliques may invest in the lateral raphe of the thoracolumbar fascia just superior to the TVA, and the most inferior/anterior fibers of the internal obliques blend with the TVA to create the conjoint tendon. Although most often I believe this muscle to function with the anterior abdominal muscles as a spinal flexor, rotator and lateral flexor, there is little doubt that the internal oblique plays dual roles.
- During forceful expiration the internal obliques not only increase intra-abdominal pressure (especially the anterior/inferior fibers) along with the TVA, rectus abdominis and external obliques, but depress the lower rib cage as well, decreasing the space within the intrathoracic cavity. Considering the internal oblique as a muscle of respiration results in potential synergies with not only anterior trunk muscles, but muscles of respiration as well. Could the internal obliques be part of a motor synergy that includes posterior serratus inferior, and the internal intercostals?
From This Point On:
These articles on functional anatomy serve as a rough draft for my 3rd publication – “Integrated Functional Anatomy” (I hope to finish by late 2015). In creating the articles for the anterior trunk muscles – rectus abdominis, external obliques and internal obliques – there is little doubt that these muscles have very similar function and behavior and could be viewed as a “synergy.” It is very likely that in the published text these muscles will be analyzed together. You will note only subtle differences between the information below and the information previously posted in the Rectus Abdominis and External Obliques articles.
- The internal obliques are part off the Anterior Oblique Subsystem (AOS). Investing in the rectus sheath, transverse abdominal fascia, and running continuous with the linea alba, through the pubic symphysis to the contralateral adductor tendons and musculature. By contributing to this synergy the internal obliques play a key role in forward bending, turning-in of the kinetic chain, and total body pronation. The AOS may also eccentrically decelerate hyper-extnesion, turning-out of the kinetic chain, and total body supination, as well as, isometrically transfer force between lower and upper extremities.
- The muscle activity and relative length of the external obliques, when viewed relative to movement impairment/postural dysfunction, matches the activity of the AOS. I have nicknamed the AOS the “Jeckyl & Hyde” system, because unlike other subsystems it may be under-active or over-active depending on the compensation pattern adopted. In Lumbo Pelvic Hip Complex Dysfunction (LPHCD) the AOS is often under-active, in Lower Leg Dysfunction (LLD) and Upper Body Dysfunction UBD this subsystem is often over-active. In Sacroiliac Joint Dysfunction (SIJD), the AOS is often over-active on the side of dysfunction and under-active on the contralateral side. Most often the over-activity of the AOS is paired with under-activity of the Posterior Oblique Subsystem (POS).
- This muscle plays a role in the arthrokinematics of the spine and lower ribcage.
- Like the rectus abdominis and external obliques the internal obliques produce anterior shear, compression on the anterior vertebral column, facet joint distraction and facet anterior glide (superior on inferior) synonymous with forward bending. For more details on how these arthrokinematics may effect the spine, check out the section on “Arthrokinematics” in the article – Rectus Abdominis
- Theoretically, a unilateral contraction of the internal oblique may laterally flex the spine contributing to facet joint compression and closing on the same side; however, the contralateral rotation and flexion force created by the internal oblique would also open the same facet joints. My guess, it is unlikely that a facet joint stuck in a compressed or closed position will have an over-active internal oblique to blame.
- Dysfunction of the costovertebral and constotransverse joints, especially those in the lower thoracic spine likely leads to reflexive inhibition of the internal obliques on the same side (inferior glide of the rib on both joints, or inferior glide of the rib at the costrotransverse joint and superior glide at the costovertebral joint). As this is often tied to a limit in rotation of the spine to one side, this may be where the function and behavior of the internal and external obliques differ. Here, we may see the internal obliques acting more like the intrinsic stabilization subsystem on the side of dysfunction. This may have something to do with receptor activity originating from the deeper layers of the thoracolumbar fascia, separate from the more superficial layers invested by the external obliques. Costovertebral joint pain can be quite debilitating and resulting in transversospinalis and intercostal muscle spasm and pain during inhalation. I would not be surprised to find a relationship between upper-body dysfunction, AOS subsystem dominance, and slightly under-active internal obliques and costovertebral/costotransverse joint dysfunction.
My Fascial Hypothesis: Large fascial sheaths not only play a role in the transmission of mechanical force, but may also play a role in dictating the function of muscular synergies. This is likely caused by reducing or increasing tone of invested musculature via reflex arcs formed between mechanoreceptors imbedded in the connective tissue and the attached musculature. In this way my view of fascia differs slightly from noted expert on the subject Tom Myers. I think of these large fascial sheaths (specifically the thoracolumbar fascia, iliotibial band, and abdominal fascial sheath) as natures “mother board.” A place for mechanical information to be communicated to the nervous system for more efficient recruitment of the muscular system. Despite having a slightly different philosophy it does not change the fact that fascia plays an important communicative role in the human body and we have Tom Myers to thank for his work.
Fascial Integration of the External Obliques – Much of the fascial integration relative to this muscle was discussed above – please see the discussion under the heading “Subsystems”, for consideration of the fascial integration between the rectus abdominis, external obliques, adductors, and synergistic recruitment of the anterior oblique subsystem.
- The Linea Alba and Rectus Sheaths: The linea alba serves as a central anchor, and along with the abdominal sheaths may serve as a way of communicating force and muscle activity between the anterior trunk musculature. Any lateral, posterior, or rotational force imparted on the truck will result in an increase in rectus abdominis, external and internal oblique, and transverse abdominis activity (3). This ensures the optimal dissipation of forces and protection of non-contractile tissues and joints. Due to a lack of bony support (i.e. no attachment to ribs) the lumbar spine in particular requires optimal synergistic function of trunk musculature to prevent excessive motion and injury.
- The one key difference between the internal obliques and the rectus abdominis and external obliques is the investment of the posterior fibers in the thoracolumbar fascia (another important communicating fascial sheath). This may result in subtle differences in muscle activity between the anterior trunk musculature and the internal obliques (an example is given in the section above on “arthrokinematics”), but more research is needed.
Behavior in Postural Dysfunction:
This muscle may be prone to adaptive lengthening and under-activity, adaptive shortening and over-activity, and is also addressed during core strength training as a prime mover.
The internal obliques like the rectus abdominis are tricky muscles to categorize. It is one of the few muscles that may adopt an increase or decrease in relative length and activity. The only way to ensure effective exercise selection is to carefully deduce the movement impairment most responsible for dysfunction, and address the muscle according to the movement impairment observed.
In Upper Body Dysfunction (UBD) the internal obliques are short/over-active, becoming synergistically dominant for a weak Intrinsic Stabilization Subsystem (ISS) and contributing to a thoracic kyphosis. This can be illustrated using an overhead squat assessment. When the individuals hands are overhead the arms fall forward or adduct, and the spine may stay relatively neutral as the over-activity of the anterior trunk muscles are balanced by over-activity of the latissimus dorsi. But, if the overhead squat is performed again with hands on pelvis the individual will collapse forward into lumbar flexion or an excessive forward lean.
In Lumbo Pelvic Hip Complex Dysfunction (LPHCD) the internal obliques are under-active as illustrated by an anterior pelvic tilt. Although crunches may not be effective, addressing the other structures involved in anterior pelvic tilt followed by Anterior Oblique Subsystem (AOS) integration is incredibly effective for regaining optimal anterior trunk muscle activity.
In Lower Leg Dysfunction (LLD) the internal obliques are either at optimal length (individual can maintain pelvis and spine neutral and tibio/torso angle parallel), or is short/over-active as illustrated by an excessive forward lean.
In short, I often do not address the internal obliques or any of the anterior trunk muscles in isolation. Although trigger point release is effective for addressing short/over-active muscles the internal obliques rarely presents with active trigger points. Practically speaking, there is no bone behind this musculature to press the muscle against for the creation of ischemic pressure. I personally have never seen active trigger points present in the internal obliques, although I have had some success in a self-administered myofascial sheer technique where one foam roll is placed on an incline and the individual assumes a side-lying position facing down the role. The individual is instructed to search for the most tender area and allow themselves to slide down the foam roll until the skin and underlying musculature is put on stretch. If you believe adaptive shortening, over-activity, and trigger points to be an issue you may attempt this technique (first on yourself, and then your client/patient), but it may be best to refer out to a manual therapist with experience treating abdominal musculature.
Stretching this muscle can be done using trunk rotation and extension. I often use a technique designed for self-administered spine mobilization, that could also be viewed as an active stretch. If you assess that static stretching is more appropriate you may hold the end range of this position (see video below).
As mentioned above activation and strengthening of the external obliques is generally done in conjunction with the other trunk flexors, or as part of anterior oblique subsystem integration.
- Rectus abdominis tendonitis
- Sports Hernia
- Diastasis Recti
- Costovetebral and costotransverse joint pain
- Intercostal pain
- Low back pain
- Thoracic pain
- Groin pain
- Sacroiliac joint dysfunction
- Pubic symphysis dyskinesis
Signs of Altered Length/Tension and Tone:
- Overhead Squat:
- Arms Fall Forward: Short/Over-active
- Anterior Pelvic Tilt: Long/Under-active
- Excessive Forward Lean: Short/Over-active
- Asymmetrical Weight Shift: Short/Over-active on side of dysfunction
- Goniometric Assessment
- Decreased Spine Extension
- Decreased Spine Rotation
- Palpation of the Internal Obliques:
- See image below for common trigger point locations and referral pain pattern for active trigger points.
Exercises involving the Internal Obliques:
Active Oblique Stretch
- Note: this exercise was designed for spine mobilization, but is a very effective active stretch for the obliques. Static stretching can be accomplished by holding end range.
Dynamic Chop Pattern:
Reactive Activation for the Core (Crunch and Catch):
Reactive Activation for the Core (Modified Mountain Climber):
Anterior Oblique Subsystem Integration (Step Up to Chest Press):
Anterior Oblique Subsystem Integration (Dynamic Lunge to Press):
- Phillip Page, Clare Frank, Robert Lardner, Assessment and Treatment of Muscle Imbalance: The Janda Approach © 2010 Benchmark Physical Therapy, Inc., Clare C. Frank, and Robert Lardner
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- Leon Chaitow, Muscle Energy Techniques: Third Edition, © Pearson Professional Limited 2007
- Tom Myers, Anatomy Trains: Second Edition. © Elsevier Limited 2009
- Shirley A Sahrmann, Diagnoses and Treatment of Movement Impairment Syndromes, © 2002 Mosby Inc.
- David G. Simons, Janet Travell, Lois S. Simons, Travell & Simmons’ Myofascial Pain and Dysfunction, The Trigger Point Manual, Volume 1. Upper Half of Body: Second Edition,© 1999 Williams and Wilkens
- Cynthia C. Norkin, D. Joyce White, Measurement of Joint Motion: A Guide to Goniometry – Third Edition. © 2003 by F.A. Davis Company
- Cynthia C. Norkin, Pamela K. Levangie, Joint Structure and Function: A Comprehensive Analysis: Fifth Edition © 2011 F.A. Davis Company
- Florence Peterson Kendall, Elizabeth Kendall McCreary, Patricia Geise Provance, Mary McIntyre Rodgers, William Anthony Romani, Muscles: Testing and Function with Posture and Pain: Fifth Edition © 2005 Lippincott Williams & Wilkins
- Brent Brookbush, Fitness or Fiction: The Truth About Diet and Exercise © 2011 Brent Brookbush – http://www.amazon.com/Fitness-Fiction-Truth-About-Exercise/dp/0615503012
- Carolyn Richardson, Paul Hodges, Julie Hides. Therapeutic Exercise for Lumbo Pelvic Stabilization – A Motor Control Approach for the Treatment and Prevention of Low Back Pain: 2nd Edition (c) Elsevier Limited, 2004
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© 2013 Brent Brookbush
Questions, comments, and criticisms are welcome and encouraged.