Abdominal Muscles

Click on the one you want to see:

  1. Rectus Abdominus
  2. External Oblique
  3. Internal Oblique
  4. Transverse Abdominus
  5. Pyramidalis

Abdominal muscles span the anterior torso from the xiphoid process, the anterior crest of the ribcage and the lumbar vertebra to the pelvic bones and the linea alba. The linea alba, in Latin, means white line. The white line passing from the xiphoid process to the pubic symphysis that separates the left and right sides of the abdominal muscles is the linea alba. A “six pack” or “eight-pack“ form is made by the rectus abdominus muscle which is divided down the middle by the linea alba. The linea alba is also the insertion for the transverse abdominus muscle, the external oblique muscle, the internal oblique muscle and the pyramidalis muscle. In the picture, at right, you can see how each of these muscles attach to the linea alba directly, or via the abdominal aponeurosis. Fibers from the external oblique muscle, the internal oblique muscle and the transverse abdominus muscle all transition into aponeurosis fibers, where they pass under the rectus abdominus. The aponeurosis allows the rectus abdominus muscle to slide on a smooth surface, as it contracts and relaxes. The horizontal white lines in the rectus abdominus muscle are where the fibers of the rectus abdominus muscle transitions from red muscle tissue to white tendon tissue. For one to have a “six-pack” they must exercise the rectus abdominus muscle, which causes the separations between the red and white fibers to become more pronounced. Also, one must lose the excess fat layer located between the skin and the rectus abdominus muscle. 

 

In order to devise an intelligent way to exercise the rectus abdominus muscle, one needs to understand which bones it attaches to, and how it moves those bones. Leg raises, for example, are commonly used with the intention of toning the lower rectus abdominus muscle. This exercise does indirectly exercise the rectus abdominus muscle because it is used to stabilize the pelvis, but it does not directly exercise it because this movement is performed by, and targets, the hip flexor muscles. While this exercise does a great job of toning the hip flexor muscles, it can lead to unsatisfactory results for toning the rectus abdominus muscle. To exercise the lower rectus abdominus muscle, one would need to use an exercise that brings the pubic bone toward the chest, for example, hip raises, while lying on one’s back with one’s feet up in the air. This exercise targets the the lower rectus abdominus muscle because it moves the insertion (pubic bone) toward the origin (ribcage). Study each of the abdominal muscles until you can visualize, and understand, how they should be exercised. Time is precious. Only a small amount of time studying the muscles of the body will save a person hours of otherwise wasted time exercising the wrong way.

 

Abdominal muscles are held together by connective tissue, for example, the linea alba. One’s large intestine, small intestine, bladder, liver and spleen are located directly beneath the abdominal muscles. Abnormalities in the connective tissue of the abdominal muscles can cause spaces to open up between the abdominal muscles. When this happens, the intestines can spill forward through the weak muscle tissue, or openings. This condition is called a hernia. Hernias can be life-threatening because they can cause a complete blockage of the intestine. Hernias occur in several places around the abdomen. The most common hernias are inguinal (inner groin), incisional (result of surgery), femoral (outer groin), umbilical (belly button) and hiatal (upper abdomen). 

 

Now that you have a general idea of where the abdominal muscles are and what they do, let us take a look at them individually.

 

The pyramidalis muscle is the smallest abdominal muscle. It is located anterior to the rectus abdominus muscle just above the pubic bone.  Its name is derived from its pyramid like shape. It originates from the anterior aspect of the pubis bone and pubic symphysis. It inserts onto the linea alba and depresses it, thereby tensing the abdominal wall. 

 

Anchored by its origin at the pubic bone, and pubic symphysis, the rectus abdominus muscle travels superiorly, in front of the intestines, liver and stomach, to its insertion onto the fifth through seventh rib and xiphoid process. Here, the terms origin and insertion are used loosely. The rectus abdominus muscle can move either the pubic bone toward the chest or the chest toward the pubic bone. This means either side can be called the origin or insertion. The insertion is simply the side that moves when a muscle contracts. If you are doing a sit-up, the ribcage is the insertion.  If you are lifting your pelvis toward your chest, the pubis bone is the insertion – a situation similar to the scalenus muscles.  

 

In geometry, oblique means an angle that is not a multiple of 90 degree angles. The oblique abdominal muscles cross the anterior abdomen at an angle, that is in fact not a 90 degree angle. There are two oblique muscles of the abdomen – the external oblique muscle (shown on previous page) and the internal oblique muscle. Serrated  finger-like extensions of the external oblique muscle weave into the serrated finger-like extensions of the serratus anterior muscle. Ribs five through twelve are the origin of the external oblique muscle. From its origin, this muscle wraps inferiorly and medially at an oblique angle, and then becomes the abdominal aponeurosis. The abdominal aponeurosis passes over the rectus abdominus muscle, and finally it inserts onto the linea alba.  When it contracts it rotates and flexes the vertebral column, while it also depresses the linea alba, thereby tensing the abdominal wall.Lower, lateral, fibers of the external oblique muscle insert onto the pubic bone, and the most lateral fibers insert onto the iliac crest. 

 

The external oblique and internal oblique muscles work together to bring the iliac crest and pubis bone toward the ribcage. These movements are called spinal flexion and rotation because ultimately the vertebral column is the portion of the skeleton that moves. The external and internal oblique muscles also support the internal organs, periteneum and abdominal contents by constricting the abdominal space. Vertebral rotation with flexion can be imagined in this way: While laying on one’s back with their hands folded behind their head, elbows out and feet in the air, to raise their hip on one side toward their ribcage on the opposing side, the internal and external intercostal muscles would be used to provide the power. This exercise could be called a crossing crunch, but this core movement is present in many other abdominal exercises. The internal and external oblique muscles can work together in this way because of the linea alba. The linea alba provides a meeting line for these two muscles. Because they are joined at the linea alba, they can function like one large muscle that can pull either side of the ribcage toward either side of the pelvis.

 

As its name implies, the internal oblique muscle is located internal to the external oblique muscle. The internal oblique muscle originates from the iliac crest, inguinal ligament thoracolumbar fascia. Lateral fibers of the internal oblique muscle wrap superiorly, from its origin, to insert onto the lower ribs. Middle fibers of the internal oblique muscle span to the xiphoid process and the linea alba, via the abdominal aponeurosis. Lowest fibers of the internal oblique muscle actually curve from their origin, at a medial/inferior angle to insert onto the inguinal ligament and the pubis bone. 

 

The word “transverse” means across. The transverse abdominus muscle basically spans across the abdomen. At its middle, the transverse abdominus muscle originates from as far back as the transverse process of the middle three lumbar vertebra via its own aponeurosis that passes between the quadratus lumborum muscle and the erector spinae muscle. Superior fibers of the transverse abdominus muscle originate from the anterior crest of the ribcage, and its inferior fibers originate from the iliac crest. All of the fibers of the transverse abdominus muscle insert onto the linea alba, via the deepest layer of the abdominal aponeurosis. The peritoneum (the lining around the intestines), liver and spleen lay directly beneath the transverse abdominus muscle. The job of the transverse abdominus muscle is to compress the abdominal viscera and constrict them to perform activities like singing or bowel compression. Since the transverse abdominus muscle constricts the waist, it is also a key muscle for the aesthetics of the body. When the transverse abdominus muscle is toned, it pulls in the waist-line. This is an important detail for body sculpting.

 

Hopefully, you now have a better understanding of where the abdominal muscles attach, and how they move the bones they are attached to. This knowledge should give you the ability to devise logical exercises for the abdominal muscles. If someone, including you, were to develop an abdominal hernia, knowing where the abdominal muscles are positioned will inform you on where the abdominal muscles are opening up to allow the hernia through. 

 

Abdominal muscles, like all muscles in the body, will spasm when they become strained or fatigued. The attachment sites for the abdominal muscles on the skeleton suffer from chronic inflammation, when the abdominal muscles spasm. Also, the bones that the abdominal muscles (in spasm) attach to become misaligned, causing the nerves trying to pass between them to become pinched. The linea alba can also become literally pulled apart at the seam by spasm of the abdominal muscles, especially the transverse abdominus muscle. The areas that will suffer from nerve impingement, chronic inflammation and associated symptoms when the abdominal muscles are in spasm include: pubic, inguinal, iliac, lumbar, anterior crest of ribcage and the xiphoid process.