Abdominal Muscles

Original Editor - Anne Millar

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Introduction[edit | edit source]

The abdominal region is supported by the anterior and posterior abdominal wall that supports the viscera and maintains the posture where there's no bony support.

The anterolateral abdominal wall formed of 4 layer skin, fascia, muscles, and peritoneum[1]. Muscles of the anterior abdominal wall consists of two vertical muscles located on the midline and bisected by linea alba; Rectus abdominis and pyramidalis and three flat muscles on the anterolateral side arranged from superficial to deep; external abdominal oblique, internal abdominal oblique, transversus abdominis.

The posterior abdominal wall consists of lumbar vertebrae, pelvic girdle, muscles, and associated fascia (quadratus lumborum, iliacus, psoas major and minor).

Acting together forming a firm wall that supports the muscles of the spine and helps to maintain an erect posture, Support internal visceral organs where there is no bone, protect the abdominal viscera from injury and help to keep them in their anatomical position. In addition, the contraction of these muscles helps in forceful expiration and to increases the intra-abdominal pressure such as in sneezing, coughing, micturating, defecating, lifting, and childbirth.[2]Have a role in preventing hyperextension.

Anterolateral Abdominal Wall[edit | edit source]

Anterior Wall Fascia[edit | edit source]

Above the umbilicus it is a single connective tissue sheet as a continuous with superficial fascia. Below the umbilicus divided into two layers, camper’s fascia the superficial fatty layer, and Scarpa's fascia the membranous deep layer. Nerves and superficial vessels run Between the two layers.[3]

Anterolateral Abdominal Wall Muscles[edit | edit source]

External obliques muscle, the most superficial anterolateral abdominal muscle its fibers run inferomedially, unilateral action results in ipsilateral side flexion and contralateral rotation of the trunk bilateral action to flex the vertebral column by drawing the pubis towards the xiphoid process[4].

Internal obliques directed superiomedially perpendicular to the external obliques it acts unilaterally for ipsilateral trunk rotation and side flexion and bilaterally to compress the abdominal viscera, pushing them up into the diaphragm, resulting in a forced expiration.

Transversus abdominis is the deepest of the abdominal muscles, it is an important core muscle and its primary function is to stabilise the lumbar spine and pelvis before movement of the lower and /or upper limbs occur[5].

Rectus abdominis is a long strap muscle that extends the entire length of the anterior abdominal wall lies close to the midline, it is an important postural and core muscle. With a fixed pelvis, contraction results in flexion of the lumbar spine. When the ribcage is fixed contraction results in a posterior pelvic tilt. It also plays an important role in forced expiration and in increasing intra-abdominal pressure.[4]

Pyramidalis with rectus abdominis it forms the anterior abdominal wall when they contract bilateral tense the linea alba.

Rectus Sheet[edit | edit source]

The three anterolateral flat muscles (obliques and transversus abdominis) form an aponeurosis on both sides that is a broad flat tendon called rectus sheat, enclose the rectus abdominis, and consists of two layers anterior and posterior layer.

Anterior layer consisting of the aponeurosis of the external obliques and half of internal obliques, the posterior layer formed by the behalf of internal obliques and transversus abdominis. join in midline forming linea alba (in which the abdominal muscles insert) extend from xyphoid process of sternum to symphysis pubis.
At a point midway between the umbilicus and symphysis pubis the posterior wall of the rectus sheet disappears and all aponeurosis sheet presented anterior forming anterior wall.

Peritoneum[edit | edit source]

Fig1. visceral and parietal peritoneum

It is a membrane that linin the abdominal cavity, covers all abdominal viscera support the viscera with abdominal muscle and provide, and divided into two layers visceral and parietal Fig1.


Posterior Abdominal Wall[edit | edit source]

Posterior Wall Muscles[edit | edit source]

Quadratus, quadrate shape on the lateral side of the posterior abdominal wall. originate from the ilium directed superior medially to insert into transverse process of L1-L4 and lower border of 12th rib. One of the functions of QL is lateral flexion and extension of the vertebral column and during the inhalation assist with the diaphragm and fixes the 12th rib.

Psoas major, located lateral to the lumbar vertebrae, originate from the transverse process of T12-L5 directed inferolateral and insert into the lesser trochanter. It flexes the thigh at the hip.

Psoas minor, doesn't present in all populations and originates from Tthe 12-L1 transverse process and inserts into pubic pectineal line.

Iliacus, originates from the iliac fossa, and with psoas major they form iliopsoas muscle that is the main flexor of the hip.

Diaphragm, the posterior aspect of the diaphragm.

Posterior Wall Fascia[edit | edit source]

It is presented between the muscles and peritoneum and is a continuous sheet with transversals fascia, it is named according to the area it covers[7]. It attaches to the lumbar vertebrae medially and thoracolumbar fascia laterally and continuous inferiorly with iliac fascia covers the psoas major muscle (psoas fascia).

Thoracolumbar fascia, consists of three layers anterior, middle, and posterior, between which the muscles enclose, quadratus lumborum between anterior and middle, deep back muscles between the middle and posterior layers.


Muscle Actions Explained[edit | edit source]

cross-section abdominal muscles

From all we mentioned before we can see that all abdominal muscles have different muscle fibers orientation and act in all three planes during movements. are linked together even by having a common site of connection or by lying fascia. When contracting one muscle other muscles will contract. For example when you aim to contract TrA at the beginning of contraction you will involve it then if you will continue or contract stronger IO will be involved then EO if you will keep going the rectus abdominis will be involved in the function.

Our body is designed to move, they work together to control the movement of the spine, pelvis, and rib cage, during gait there is relatively a counter-rotation between the upper and lower part and the arm and leg are moving in opposite direction to each other.

During normal gait, there is a time when rectus abdominis and external obliques at one side act eccentrically to decelerate the anterior pelvis tilting created by the extension of the hip of that side and RA and external obliques of the other side work eccentrically to control thoracic extension and rotation created by the extension of the shoulder.

"To describe the function of abdominal muscle it can be easily demonstrated from the supine position and flex the spine as this movement is controlled by the brain but this isn't how they actually work" stated Dr, Gray a physical therapist[9]. During mid-range of spine flexion, RA and external obliques shorten and the transversus abdominis lengthen and work together and internal obliques generate maximum of its force[10].

During the exercise program, we need to involve muscles in functional exercise for better outcome[11].


Clinical Relevance[edit | edit source]

The abdominal viscera can be palpated through the abdominal wall and their place can be visually marked, the umbilicus is the most marked it is fond usually midway between the xiphoid and symphysis pubis. The linea alba splits the rectus abdominis into two half and extends from a vertical groove that presented from xiphoid process.

Fig2. 9 regions of abdominal cavity

The abdomen is divided into 9 regions by two horizontal and two vertical plans, these regions are with benefit to describe the location of pain, identify the visceral organs, and in surgical procedures Fig2.

Transverse abdomimis as a deep abdominal muscle and one of the main important core muscle that contributes to supporting lumbopelvic stability and deficit in its function affects our back causing low back pain (LBP). We need to include it in our rehabilitation program[13]

As we mentioned before the abdominal muscles together participate to maintain your erect posture and prevent hyperlordosis pf vertebral column, hence the abdominal muscles have are flexors at the of the vertebral column. Weakness of lumbar extensors with insufficient abdominal muscle contraction in a way that can not oppose the lordosis participate in developing the hyperlordosis.

Deficit in the abdominal wall muscles congenital from birth or acquired postoperatively as a result of a poor wound healing, wound infection, or acquired weakness after pregnancy and labor for example. can manifest in the form of hernia congenital or acquired.

Fig3. acquired hernia

Congenital hernia happens during infant development as a result of embryological malformations or weakness in the neonatal abdominal wall, it may be fatal in some cases and need urgent and surgical intervention as; gastroschisis, or resolve without need to surgical intervention as in umbilical hernia.

Acquired hernia happens in the area of weakness and varies in its severity[14]:

Umbilical hernia that is more serious and has a higher rate of morbidity in adult more than infants and may need surgical intervention. Inguinal hernia protrudes at the inferior border of anterolateral muscles. Epigastric hernia, above the umbilicus through the midline of the linea alba. Spigelian hernias, and incisional hernia as a result of postoperative incision.

Rectus diastasis happens due to prolong transverse stress on linea alba during pregnancy, or post-menopausal women.

Psoas sign, that indicates there is irritation to the iliopsoas muscle group and you can test it by passive flexion of thigh if there is pain in the lower abdomen the test is positive when it is presented on the right side may be an indication of appendicitis.[15]

Physical Therapy Intervention[edit | edit source]

Abdominal exercises need to be gradually progressed from how to activate muscles and maintain contraction to integrate them with functional movement, but there's special considerations, precaution, and exercise modification that we will take these exercises for a patient with a hernia.

  • Abdominal draw in exercise, easy to apply, target mainly transversus abdominis as well as the diaphragm it's an important respiratory exercise[16]. Exercise can be progressed by adding external resistance, upper limb or lower limb movement while holding abdomen drawing in. Patients with lumbar hyperlordosis draw-in exercise from borne hip extension increase the activity of gluteus maximus, weakness GM speed up lumbar hyperhidrosis, and increase the load on lumbar spine and pelvis so this exercise will be with benefit[17].
  • Curl up exercise, target rectus abdominis, transverse abdominis, and obliques in addition to hip flexors, chest, and neck, start the exercise with slow movement, few repetitions and make sure the back is in contact with the floor and eccentric curl up is most effective at angle at 30∘.[18]


  • Bridging, modified bridging with hip abduction or unstable surface show to increase core stability, trunk control. The activation of internal abdominis, rectus abdominis along with erector spine is greater in modified bridging when compared to standard bridging[20].


  • William protocol of spine flexion has a positive effect on lumbar hyperhidrosis, back pain, increased flexibility of hip flexor and back extensions, abdominal muscle strength, and hamstring flexibility, examples of William exercises[22]:
    • Pelvic tilt, from flat position and knees in flexion try to flatten your back without pushing down with your leg
    • Single and double knee to chest
    • Partial sit-up, with maintaining the pelvic tilt curl your head and shoulder off.
    • Hamstring stretch
    • Hip flexor stretch and squat.


  • Plank and pilates exercises activate and strengthen core muscles along with abdominal muscles.

For more exercise descriptions see Core stability and Lumbar motor control training

References[edit | edit source]

  1. Flament JB. Functional anatomy of the abdominal wall. Der Chirurg; Zeitschrift fur alle Gebiete der operativen Medizen. 2006 May;77(5):401-7.
  2. Drake RL, Vogyl AW, Mitchell AW. Gray's anatomy for students. 3rd edition. Philadelphia: Churchill Livingstion Elsevier; 2015. 282p.
  3. Anterior abdominal wallhttps://teachmeanatomy.info/abdomen/muscles/abdominal-wall/
  4. 4.0 4.1 Drake RL, Vogyl AW, Mitchell AW. Gray's anatomy for students. 3rd edition. Philadelphia: Churchill Livingstion Elsevier; 2015. 286p
  5. Lee D. The Pelvic Girdle. 2nd Ed. Edinburgh: Churchill Livingstone, 1999.
  6. Anatomy Zone. Muscles of the Anterior Abdominal Wall-3D Anatomy Tutorial. Available from: http://www.youtube.com/watch?v=mvOajxO8mXO [last accessed 11/07/15]
  7. Posterior abdominal wallhttps://teachmeanatomy.info/abdomen/muscles/posterior-wall/
  8. Anatomy Zone. Muscles of the Posterior Abdominal Wall - 3D Anatomy Tutorial. Available from: http://www.youtube.com/watch?v=ovQYBAiv8cI[last accessed 17/5/2020]
  9. ACE, Functional anatomy of abdominal muscles
  10. clinical gait, anatomy, and biomechanics of abdominal wall muscle.
  11. McGill S. Core training: Evidence translating to better performance and injury prevention. Strength & Conditioning Journal. 2010 Jun 1;32(3):33-46.
  12. tendosport. How Abdominal Muscles Work. Available from: http://www.youtube.com/watch?v=4MeLHSjESlU[last accessed 20/5/2020]
  13. Selkow NM, Eck MR, Rivas S. Transversus abdominis activation and timing improves following core stability training: a randomized trial. International journal of sports physical therapy. 2017 Dec;12(7):1048.
  14. Flynn W, Vickerton P. Anatomy, Abdomen and Pelvis, Abdominal Wall. InStatPearls [Internet] 2019 Dec 9. StatPearls Publishing.
  15. https://en.wikipedia.org/wiki/Psoas_sign
  16. Oh YJ, Park SH, Lee MM. Comparison of Effects of Abdominal Draw-In Lumbar Stabilization Exercises with and without Respiratory Resistance on Women with Low Back Pain: A Randomized Controlled Trial. Medical Science Monitor: International Medical Journal of Experimental and Clinical Research. 2020;26:e921295-1.
  17. Kim TW, Kim YW. Effects of abdominal drawing-in during prone hip extension on the muscle activities of the hamstring, gluteus maximus, and lumbar erector spinae in subjects with lumbar hyperlordosis. Journal of physical therapy science. 2015;27(2):383-6.
  18. Ha SY, Shin DC. The effects of curl-up exercise in terms of posture and muscle contraction direction on muscle activity and thickness of trunk muscles. Journal of Back and Musculoskeletal Rehabilitation. 2020 Feb 28(Preprint):1-7.
  19. Health e-University. How to do a Curl Up: Health e-University. Available from: http://www.youtube.com/watch?v=lsWQ0XpiNkE[last accessed 25/4/2020
  20. Yoon JO, Kang MH, Kim JS, Oh JS. Effect of modified bridge exercise on trunk muscle activity in healthy adults: a cross sectional study. Brazilian journal of physical therapy. 2018 Mar 1;22(2):161-7.
  21. Physio Fitness | Physio REHAB | Tim Keeley. Glute Bridges and back pain - Don't flex the spine! | Feat. Tim Keeley | No.70 Physio REHAB. Available from: http://www.youtube.com/watch?v=SwyDMwpcW38[last accessed 25/4/2020
  22. Fatemi R, Javid M, Najafabadi EM. Effects of William training on lumbosacral muscles function, lumbar curve and pain. Journal of back and musculoskeletal rehabilitation. 2015 Jan 1;28(3):591-7.
  23. Ccedseminars. Williams Flexion Exercises for Lumbar Spine. Available from: http://www.youtube.com/watch?v=757ucsakxoc[last accessed 21/5/2020]