Anterior Oblique Subsystem (AOS)

Anterior Oblique Subsystem Integration

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


The Anterior Oblique Subsystem (AOS) is comprised of:


  • External Obliques
  • Abdominal Fascia/Linea Alba
  • Contralateral Anterior Adductors
  • Internal Obliques
  • Rectus Abdominis
  • Note: The internal obliques and rectus abdominis are not traditionally viewed as muscles of the AOS.  However, based on my considerations of anatomy, function, and available research, and observations in practice, adding these muscles to this subsystem adds congruence to our understanding of muscular synergies, motor behavior, and predictive models of movement impairment.


Function (Brief):

Stabilization of the anterior kinetic chain (including the joints of the pubic symphysis, hip and lumbar spine), transfer of force between lower and upper extremities, integrated (whole body) pushing movements, “turning-in” of the kinetic chain, eccentric deceleration of total-body supination.


Functional Arthrokinematics:
The Anterior Oblique Subsystem (AOS) is an important stabilizer of the anterior kinetic chain.  This subsystem has little direct effect on joint arthrokinematics (when compared to the Posterior Oblique Subsystem (POS) and the sacroiliac joint); however, it is indirectly involved in stabilization of the lumbar spine, thoracic spine, rib cage, pubic symphysis, and hip joint.

The AOS is responsible for eccentric deceleration of rotation and extension of the lumbar and thoracic spine – a movement pattern that may lead to facet joint and posterior disk compression and has been indicated in lumbar spine injury.  The AOS is also involved in eccentric deceleration of an anterior pelvic tilt, especially during standing, pushing motions.  As an anterior pelvic tilt includes lumbar spine extension, sacroiliac joint (SIJ) motion, and if not symmetrical may include rotation; any dyskinesis of the SIJ, lumbar spine, or change in pelvic rotation may indicate AOS involvement.

The AOS directly stabilizes the pubic symphysis, although the most notable relationship in the AOS synergy relative to this joint is the fascial continuity between rectus abdominis (a muscle not traditionally viewed as an AOS muscle) and the adductor longus.  Although relatively rare, pubic symphysis dyskinesis does occur and can be painful.  Optimal function of the AOS bilaterally, ensures control of rotation, superior/inferior glide, and other accessory motions at the pubic symphysis associated with the normal pelvic torsion during gait.

Asymmetrical dysfunction in the AOS may lead to dyskinesis of the lumbar and thoracic spine, SI joint, and pubic symphysis via rotation of the spine and/or innominate. This dysfunction may present as rotation, lateral flexion, a hip hike, anterior or posterior tilting of one or both sides of the pelvis, and dyskenisis of the pubic symphysis.  Note that asymmetrical postural dysfunctions like these have been correlated with injury.  At the very least, these dysfunctions will increase strain on the human movement system leading to pattern overload and the cumulative injury cycle.


Illustration of pelvis and sacrum torsion… consider how the AOS would be lengthened on the side closest to us (right side), and shortened on the other (left side). -


Integrated Function:

These muscles play an important role in transferring force between lower and upper extremities and stabilizing the anterior kinetic chain.  The AOS is stressed most during pushing motions, and “turning-in” of the kinetic chain.  This musculature also functions as an eccentric decelerator of “total-body supination” (spinal extension and rotation, hip extension, abduction and external rotation).  The importance of decelerating total body supination can be seen during the “loading phase” of a throw or swing, or when an individual is hit from the front – for example, a football lineman being hit in the upper-body by an opponent.  Along with the optimal function of our ISS (Intrinsic Stabilization Subsystem) and POS (Posterior Oblique Subsystem) the AOS  ensures optimal stabilization, alignment and movement of the LPHC, and optimal arthrokinematics of our hip joint and lumbo-sacral joints.  Although a bit simplistic, it may be worth considering this the anti-rotator/anti-extension subsystem – our number one defense against lumbar extension injuries.


Motor Behavior:

The AOS could be termed “the Jeckyl & Hyde”  of the core subsystems.  In Upper Body Dysfunction (UBD) the AOS is over-active, in Lumbo Pelvic Hip Complex Dysfunction (LPHCD) the AOS is often under-active, and in Lower Leg Dysfuction (LLD) the AOS is either not involved, over-active in the case of an excessive forward lean, or under-active as is the case of LLD presenting with an anterior pelvic tilt.  The behavior and relative length of the AOS during Sacroiliac Joint Dysfunction (SIJD) is a bit more involved than this article will consider, but further information can be found by following this hyperlink to “Sacroiliac Joint Motion and Predictive Model of Dysfunction

In Upper Body Dysfunction UBD the AOS is overactive/dominant and is paired with under-active/inhibited POS.  This may be most obvious in those individuals who exhibit an excessive thoracic kyphosis (flexion of the thoracic and lumbar spine).  However, the factors contributing to dominance of the AOS in upper-body dysfunction may be far more intricate and nuanced.  Often, during an overhead squat assessment, an individual will present with UDB signs (arms fall forward, scapula elevate), but until the overhead squat is done again with the hands on the waist the AOS dominance signs will not present (flexion of the lumbar/thoracic spine and/or excessive forward lean). The increase in latissimus dorsi activity in upper-body dysfunction may lead to an alteration in the motor pattern used to stabilize the LPHC.  That is – synergistic dominance of the latissimus dorsi leads to inhibition of the Intrinsic Stabilization Subsystem (ISS); either due to changes in arthrokinematics or the adoption of a compensatory pattern that results in a latent firing pattern of the ISS and eventual de-conditioning.  In time, the lack of intrinsic stabilization creates a decrease in activity threshold for recruitment of the global trunk musculature including the AOS (global muscles become active for movements that were previously to “light” to initiate activity) to stabilize the LPHC leading to over-activity.  In this case it is likely best to avoid exercise that would further increase AOS activity and strength – examples may include planks, crunches, chops, and standing push patterns.  Instead focus on ISS activation and static stabilization including the drawing-in maneuver.

          In the most common Lumbo Pelvic Hip Complex Dysfunction (LPHCD) ( an Anterior Pelvic Tilt – APT) the AOS is under-active, and is paired with under-activity of the POS.  In this case the AOS is not capable of tilting the pelvis posteriorely or maintaining enough lumbar flexion to attain a neutral spine, a scenario that is concurrent with the large and synergistically dominant latissimus dorsi and iliacus pulling the individual into lumbar extension.  Verbal, visual and tactile cuing of a posterior pelvic tilt to reinforce optimal pelvic alignment and integrating the AOS (legs w/ push) is effective for improving this dysfunction.  Note: The use of an AOS integration exercise with an individual who has an APT will often lumbo-pelvic hip alignment, but in some cases results in an excessive forward lean.  In this case it is appropriate to follow an AOS integration exercise with a POS integration exercise.

  The AOS is generally not involved in Lower Leg Dysfunction (LLD); however, some individuals present with LLD and an excessive forward lean or anterior pelvic tilt.  In the case of an excessive forward lean avoid exercise that could increase the strength and activity of this musculature, and focus instead on ISS activation and POS integration.  In the case of an anterior pelvic tilt, consider the suggestions discussed for LPHCD above.

Additions to the AOS:


Relationship between adductor longus and rectus abdominis tendons –


Rectus Abdominis:

Could the Rectus Abdominis be part off the Anterior Oblique Subsystem (AOS)?  The rectus abdominis is enveloped by the rectus sheath and transverse abdominal fascia and is bisected by the linea alba.  These structures aid in the transmission of force and may influence the tonicity of the muscles invested.  This would include the rectus abdominus and obliques.  Further the rectus abdominis tendons and linea alba invest with superficial fascia that continues into the anterior adductor tendons.  In essence the abdominal fascia runs with some continuity from the abdomen, through the pubic symphysis, into the tendons of the anterior adductors and superficial fascia of the anterior thigh.  The idea of fascial continuity, and the idea of muscular synergy recruitment for trunk motion are central ideas that have lead to the conceptualization of core subsystems (muscular slings).  Although the AOS is traditionally viewed as the external oblique, abdominal fascia, and contralateral adductor (excluding the rectus abdominis) – the most notable fascial relationship is actually between the tendon of the rectus abdominis and the tendon of the adductor longus (see image below).

The rectus abdominis is active during all functions of the AOS. Forward bending, turning-in of the kinetic chain, total body pronation, eccentric deceleration of hyper-extnesion, turning-out of the kinetic chain, and supination, as well as, the transfer of force between lower and upper extremities – all require optimal activity of the rectus abdominis.

Further, the muscle activity and relative length of the rectus abdominis, when viewed relative to movement impairment/postural dysfunction, matches the activity of the AOS perfectly.  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 and so is the rectus abdominis, in Upper Body Dysfunction UBD the AOS is overactive and so is the rectus abdominis, in Lower Leg Dysfunction (LLD) the relative position of the pelvic dictates the activity of the AOS, but the rectus abdominis matches that activity.  In Sacroiliac Joint Dysfunction (SIJD), the AOS is often over-active on the side of dysfunction and under-active on the contralateral side, although it is not possible to work a single side of the rectus abdominis injury and pain patterns would suggest a pairing once again.   Most often the over-activity of the AOS is paired with under-activity of the Posterior Oblique Subsystem (POS).

In my humble opinion, the ideas above should lead to the inclusion of the rectus abdominis in the AOS.  Exercise selection for the rectus abdominis should be considered in conjunction with this subsystem for all modalities – release, lengthening, activation, core exercise, and subsystem integration in fitness, rehab, and performance enhancement training.

Internal Obliques:

The superficial abdominal fascia and linea alba are invested by the external obliques, internal obliques and rectus abdominis.  This fascial continuity, along with shared function makes it hard to point to instances where these muscles are not acting synergistically. The internal obliques assist in spine rotation with a co-contraction of the contralateral external oblique. Without this co-contraction the external obliques would produce lateral flexion, and/or pull the rectus abdominis and linea alba laterally resulting in inefficient motion. 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 inseparable pairing.

The internal obliques are also synergist for all motions and activities associated with the AOS, from trunk stabilization and transmission in force to flexion and ipsilateral rotation of the spine, to eccentric deceleration of supination.  Although, likely third in ability to produce force behind the external obliques and the prime mover, the rectus abdominis, this muscle is involved in all AOS activities.

Finally, research shows that the internal obliques are active during potentially the most important function of the AOS.  The internal obliques are an important stabilizer when the body resists a significant external load, especially when that load is anterior to posterior. 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 (ISS); however, 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 “3″ below and the article 3 Classic Studies in Core Muscle Recruitment).

Assuming this muscle is part of the global muscular system, this muscle would have the same behavior as the external obliques during postural dysfunction, and result in the same exercise selection.  If this muscle by chance, happens to be part of the the ISS than we would consider it during ISS/TVA activation, however this would still not change our exercise selection.

Subsystems, Postural Dysfunction, and Integrated Exercise Selection:

The summaries below are intended for a quick reference in practice and do not illustrate all possible scenarios.

Subsystem Activity Based on Postural Dysfunction:

Subsystem ISS POS LS AOS DLS  
Upper Body Dysfunction Underactive Underactive   Overactive  
LPHC Dysfunction Underactive Underactive   Underactive Overactive
SIJ Dysfunction Underactive Underactive Underactive on affected side Overactive on Contralateral Side Underactive on affected Side Overactive on Contralateral Side Overactive
Lower-leg Dysfunction   Underactive Underactive   Overactive

Effect on Exercise:

  Activate Subsystem Integration Limit/Inhibit
Upper Body Dysfunction ISS POS AOS
LPHC Dysfunction ISS AOS  –> POS DLS
SIJ Dysfunction ISS POS on Affected Side DLS on Affected Side
Lower Leg Dysfunction ISS




Subsystem Integration  Common Behavior Clue  
Intrinsic Stabilization
TVA Activation Under-active “TVA and Friends”
Posterior Oblique
Legs with Pull (Row) Under-active “Almost always underactive”
Single Leg w/ Shoulder Series; Frontal Plane Preferred   Dysfunctional “Victim system”
Anterior Oblique
Legs with Push (Chest Press) Over-active  > Underactive “Jeckyl & Hyde”
Deep Longitudinal (DLS) Inhibit Over-active “Almost always overactive”


Exercise Selection

If movement assessment leads us to believe that the AOS is underactive (Anterior Pelvic Tilt) consider the following changes to your exercise programming.

Core:  It may be beneficial to add planks, crunches, and chop patterns to the core portion of the integrated warm-up.

Subsystem Integration/Whole Body Exercise Selection: The exercises used to integrate the AOS can be summarized as “legs with push.”  Because of the inherent difficulty of these exercises it may be necessary use a static chop progression and standing chest press progression as prerequisites before starting the integrated exercise progression below.

Resistance Training:  There is no difference between the exercises selected for Subsystem Integration found on the “Integrated Warm-Up Template” and the Whole Body Movement used in the “Resistance Training Template.”  If someone presents with an under-active AOS it may be ideal to continue using “legs w/ push” movements during the Whole Body Movement.  If you choose to use the same exercise for both Subsystem Integration and Whole Body Movement, than the last exercise of your integrated warm-up is also the first exercise of your resistance training program; there is no need to repeat sets.  If someone has “cleaned-up” the majority of their dysfunction you can add other whole body movement patterns to their resistance training routine that may or may not relate to their movement dysfunction.

Progress chest and back movements to exercises without a stable back support.  For example, standing chest press, and/or kneeling pull downs.  It may also be wise to limit overhead pressing for shoulder movements until better LPHC stabilization is attained.

We could say that once you have completed an integrated warm-up; your knowledge of subsystems and movement assessment will influence, but not dictate, your resistance training exercise selection.

If movement assessment leads us to believe that the AOS is Overactive (Upper Body Dysfunction, Excessive Forward Lean) consider the following changes to your exercise programming.

Core:  It may be beneficial to avoid planks, crunches, and chop patterns in the core portion of the integrated warm-up and spend more time on TVA activation and bridges.

Subsystem Integration/Whole Body Exercise Selection: Avoid AOS integration exercise and focus on POS integration (See Posterior Oblique Subsystem (POS) Article for more on those exercise): The exercises used to integrate the POS can be summarized as “legs with pull.”

Resistance Training:  If someone presents with an over-active AOS it may be ideal to continue using “legs w/ pull (POS Integration)” movements during the Whole Body Movement.

Regress chest movements with a back support.  For example, bench press or dumbbell press on a stability ball.  It may also be wise to limit overhead pressing for shoulder movements until better LPHC stabilization is attained.


AOS Subsystem Integration Progression:

  • Standing Static Chop Pattern and Progressions
  • Standing Chest Press and Progressions
  • Legs w/ Push
  1. Step-Up to Chest Press
  2. Step-Up to Unilateral Chest Press
  3. Step-Up to Balance to Chest Press
  4. Step-Up to Balance to unilateral Chest Press
  5. Frontal Plane Step-Up to balance to Chest Press
  6. Frontal Plane Step-Up to balance to unilateral Chest Press
  7. Transverse Plane Step-Up to balance to Chest Press
  8. Transverse Plane Step-Up to balance to unilateral Chest Press
  9. Reverse Lunge to Chest Press
  10. Reverse Lunge to Contra-lateral Chest Press
  11. Transverse Plane Lunge to Contralateral Chest Press
  12. Reverse Lunge to Single Leg Balance to Chest Press
  13. Reverse Lunge to Single Leg Balance to Unilateral Chest Press
  14. Transverse Plane Lunge to Single Leg Balance to Contralateral Chest Press


Stretching, Core, and Integrated Movement Patterns for addressing the Anterior Oblique Subsystem (AOS)

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.

Ball Crunch:

Side Plank:

Static Chop:

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):

Core Power:



  1. Dr. Mike Clark & Scott Lucette, “NASM Essentials of Corrective Exercise Training” © 2011 Lippincott Williams & Wilkins
  2. Donald A. Neumann, “Kinesiology of the Musculoskeletal System: Foundations of Rehabilitation – 2nd Edition” © 2012 Mosby, Inc.
  3. 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



© 2013 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged!


Anterior Oblique Subsystem (AOS) — 32 Comments

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  7. Hi Brent, could you talk about your source for the word “subsystems”, and the difference btw/crossover of subsystems and myofascial slings. Thank you!

    • I first heard of subsystems through NASM… I do not believe there is any difference between subsystems and myofascial slings. Any references you have would be greatly appreciated, the research overall seems very scarce. However, the concept does a wonderful job of explaining activity and function of core musculature.

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  10. Hi brent,
    I read the series of your articles that deals with “Core Subsystems”.
    Good articles and great methodological connection between the theory and practice.

    I have an Msc degree in Exercise and Sport Science, i know and read most of the the literature that published from the figures in that knowledge area (core):
    – the australian team – Hodges, Hides and Richardson.
    – the candian group – Stu Mcgill and his colleagues and students.
    – Andry Vleeming and his group from the netherlands.
    – Thomas myers (with continue his mentors) – anatomy trains and/or myofascial meridians/slings.

    The approach that you present here is very interesting, it seems (correct me if im wrong) that you do a synthesis of your wide knowledge with the basic idea of the subsystems (that name and approach is new to me).
    I will be happy for your Proffesional comment and more happy if you write some references that you rely on them, because i wand to read and learn ;-)

    Thanks in advance
    (sorry about the poor english)


    • Hey Roy,
      You are absolutely right… I am relying on my knowledge base, my theoretical models of postural dysfunction, and previous experience and should put some more effort into a lit review. My first introduction to the subsystems was via the NASM (National Academy of Sports Medicine) texts. Part of the reason why this blog exists is for me to “vet” my new ideas and continue refining my writing before compiling a formal text. Comments like yours are exactly what I need to ensure I continue to grow and deliver the product everyone wishes to see.
      The Core Subsystems articles have become some of my most popular articles to my great surprise. It is obvious that I need to increase my efforts to refine these writings.
      Thanks again,

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  13. Pingback: External Obliques |

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  15. I read this article and it was very well written. Because of attending your workshops, I was able to pretty much comprehend everything. Thank you for everything.

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  27. very informative and usefull info.
    my case is a medical problem I have had a number of years.
    I have ataxia(or so they say)but is it?i have been having differing opinions as to my problem over a number of years.
    at one time I was examined in a hospital by neurologists,professors,doctors phisios,chiropractors,muscular skeletal specialists and the like.
    they have given me every possible medical tests(x ray,mri scan of brain and spine,blood tests for every possible medical condition and have all come back ok.
    there is difference of opinion between even top neurologists but I believe it is a muscle weakness problem.
    do you have a clinic which people like myself can attend in this country because bupa and the nhs are unable to sort out a problem like mine.

  28. Brent,

    I’ve been following you for a while and your articles have really helped me with LPHCD. Glutes are firing again and other muscles are starting to feel freer which is amazing. THANK YOU!

    There is one thing I can’t figure out though. I have a bit of a twisting dysfunction, most likely due to SIJD. The rectus is overactive on the right and I can’t seem to get it firing on the left side (specifically in the lowest portion of the muscle). You mention in this article that it is not possible to isolate one side of the rectus, so what should I do? All exercises (chop and lift, oblique curls, etc) only seem to recruit the right side and I sometimes cramp up.

    I’ve read your article on SIJD. I am a massage therapist and it still gave me a bit of a headache but I was able to follow most of it. I believe my dysfunction is on the right side. Do you think that if I follow the corrective exercise routine that this problem will resolve eventually?

    • If the program was going to work, it should have had some effect the first time you tried it.
      It is possible that you have joint dyskinesis that requires manual intervention (pubic symphysis, sacroiliac and lumbar facet dysfunction). You may consider seeing a physical therapist for an in-person evaluation.

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