Dominic Stone
The abdominal muscles are located between the rib cage and the pelvis, at the front of the body. There are five main abdominal muscles: pyramidalis, rectus abdominis, external obliques, internal obliques, and transversus abdominis. These muscles help hold organs in place, support the body during movement, and assist in breathing. The rectus abdominis is the muscle that creates the `six-pack` look when visible. The external and internal obliques are responsible for twisting and turning movements, while the transversus abdominis is the deepest muscle layer, providing stability to the trunk and spine. Together, these abdominal muscles form the core, along with the intrinsic back muscles, and contribute to overall core stability, strength, and posture.
| Characteristics | Values |
|---|---|
| Number of abdominal muscles | 5 main muscles |
| Location | Between the ribcage and pelvis at the front of the body |
| Types | Rectus Abdominis, External Obliques, Internal Obliques, Transversus Abdominis, Pyramidalis |
| Function | Holding organs in place, supporting the body during movement, twisting and turning the trunk, regulating breathing, protecting the spine |
| Appearance | The Rectus Abdominis is the "six-pack" muscle, while the External Obliques are the V-shaped muscles |
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What You'll Learn
- Rectus Abdominis: a pair of muscles that run down the middle of the abdomen
- Transversus Abdominis: deepest muscle layer, stabilises the trunk
- External Obliques: largest of the flat muscles, sit at the bottom of the stack
- Internal Obliques: smaller, sit on top of external obliques, inside hip bones
- Pyramidalis: a small, triangular vertical muscle
Rectus Abdominis: a pair of muscles that run down the middle of the abdomen
The rectus abdominis is a pair of long, straight muscles that run down the middle of the abdomen, from the ribs to the pelvis. They are divided into two segments by a muscle called the linea alba. The rectus abdominis is responsible for holding internal organs in place, keeping the body stable during movement, and regulating breathing. It is also the muscle that gives people a ""six-pack" when they have a trim, fit abdomen.
The rectus abdominis is the muscle that people are usually referring to when they talk about their "abs". It is one of the five main abdominal muscles, along with the pyramidalis, external obliques, internal obliques, and transversus abdominis. These muscles work together to support the body's trunk and hold organs in place.
The rectus abdominis is a very long, flat muscle that extends along the whole length of the front of the abdomen. It is separated from its fellow on the opposite side by the linea alba, which runs down the centre of the abdomen. The muscle is innervated by thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves.
The rectus abdominis plays an important role in respiration, especially during forceful exhalation, such as after exercise or in certain medical conditions. It also assists in flexing the trunk of the body, such as when doing a crunch or sit-up exercise. To isolate the rectus abdominis during exercise, the knees should be bent to minimise the engagement of the hip flexors.
Strains and injuries to the rectus abdominis are common, especially with weak abdominal muscles. A rectus sheath hematoma is an accumulation of blood in the sheath of the muscle, causing abdominal pain. This condition may be caused by the rupture of the epigastric artery, muscular tear, anticoagulation, coughing, pregnancy, abdominal surgery, or trauma.
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Transversus Abdominis: deepest muscle layer, stabilises the trunk
The transversus abdominis is the deepest abdominal muscle layer. It is located underneath the rectus abdominis and obliques. It wraps around the waist to support the spine, helping to prevent instability and supporting the lower back.
The transversus abdominis is a broad, paired muscular sheet found on the lateral sides of the abdominal wall. It is one of the anterolateral abdominal wall muscles, which also include the rectus abdominis and pyramidalis. These muscles are located towards the front of the body, between the ribs and the pelvis.
The transversus abdominis has several origin points, including the lateral one-third of the superior surface of the inguinal ligament and the anterior two-thirds of the inner lip of the iliac crest. From these origin points, the muscle fibres course horizontally over the lateral abdominal wall towards the midline, perpendicular to the linea alba.
The main roles of the transversus abdominis are to stabilise the trunk and maintain internal abdominal pressure. It helps to regulate breathing and protects the internal organs by creating intra-abdominal pressure. It also helps with movement between the ribcage and the pelvis, allowing the trunk to be in constant motion.
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External Obliques: largest of the flat muscles, sit at the bottom of the stack
The external obliques are a pair of muscles, one on each side of the rectus abdominis. They are the largest of the flat muscles and sit at the bottom of the stack. They are the outermost of the three flat abdominal muscles of the lateral anterior abdomen. The external obliques are broad, thin, and irregularly quadrilateral. They are not visible in most humans due to subcutaneous fat deposits and the small size of the muscle.
The external oblique muscle originates from the external surfaces of the lower eight ribs. The muscle fibres fan out towards the midline and inferior margins of the abdomen. The most posterior fibres course almost vertically, while the remainder passes anteromedially. The external obliques function to pull the chest downwards and compress the abdominal cavity, increasing intra-abdominal pressure. This pressure helps protect the internal organs, similar to the function of the rectus abdominis.
The external obliques also cause ipsilateral lateral flexion of the trunk and contralateral rotation of the trunk when they contract unilaterally. Bilateral contraction flexes the trunk anteriorly, increasing intra-abdominal pressure, which is useful in processes such as breathing, singing, and defecation. The external obliques allow the trunk of the body to twist, with the external oblique on the opposite side of the direction of the twist controlling the movement. For example, when twisting to the left, the right external oblique is engaged.
The external oblique is supplied by the ventral branches of the lower six thoracoabdominal nerves and the subcostal nerve on each side. The cranial portion of the muscle is supplied by the lower intercostal arteries, while the caudal portion is supplied by branches of either the deep circumflex iliac artery or the iliolumbar artery.
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Internal Obliques: smaller, sit on top of external obliques, inside hip bones
The internal obliques are one of the five main abdominal muscles. They are a pair of muscles that sit on top of the external obliques and just inside the hip bones. They are much thinner and smaller than the external obliques. The internal obliques work with the external obliques to allow your trunk to twist and turn.
The internal obliques are responsible for twisting and turning, controlling the opposite side of the movement. For example, when you twist to the right, you are contracting the right internal oblique and the left external oblique at the same time. Because of this, internal obliques are sometimes called "same-side rotators".
The internal obliques originate on the inguinal ligament, which is a ligament that runs from the anterior iliac spine to the pubic bone. They also originate on the anterior iliac crest. The fibres of the internal obliques are oriented perpendicularly to those of the external obliques.
The internal obliques can function bilaterally, meaning both sides work together, or unilaterally, meaning one-sided. Bilaterally, they flex the trunk and compress its contents. Unilaterally, they flex the trunk and rotate it to the same side.
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Pyramidalis: a small, triangular vertical muscle
The abdominal muscles are located between the ribcage and the pelvis at the front of the body. They are made up of five pairs of muscles, two of which are vertical and run down the middle of the body. The pyramidalis muscle is one of these two vertical abdominal muscles.
The pyramidalis is a small, triangular vertical muscle. It is located at the base of the pubic bone. It sits in front of the rectus abdominis, attaching to the linea alba. The rectus abdominis is a pair of muscles that run down either side of the middle of the abdomen, from the ribs to the pelvis. The pyramidalis is also situated just above the external and internal obliques, which are flat muscles stacked on top of each other towards the sides of the trunk.
The pyramidalis is an important muscle that helps maintain internal pressure in the abdomen. It is one of the five main abdominal muscles, along with the rectus abdominis, external obliques, internal obliques, and transversus abdominis. These abdominal muscles work together to support the trunk, allow movement, and hold organs in place.
Interestingly, about 20% of people do not have a pyramidalis muscle. Despite this, those who do have it can still benefit from its presence in their abdominal structure. The pyramidalis is part of the core, which includes the abdominal muscles and the lower back muscles. Together, these muscles help to keep the body stable and balanced, as well as protect the spine.
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Frequently asked questions
The abdominal muscles are the muscles forming the abdominal walls, which is the portion of the trunk connecting the thorax and pelvis. There are five main abdominal muscles: pyramidalis, rectus abdominis, external obliques, internal obliques, and transversus abdominis.
The rectus abdominis is composed of paired sheets of long, straight muscles that are located in the middle of the abdomen, from the ribs to the pelvis. These are the muscles that you use to flex yourself forward and are the muscles that create a six-pack look.
The external obliques are a pair of muscles, one on each side of the rectus abdominis, and are the largest of the flat muscles. They run from the sides of the body toward the middle and allow the trunk to twist from side to side. The internal obliques are a pair of muscles on top of the external obliques, just inside the hip bones. They are much thinner and smaller than the external obliques but work together with them to allow the trunk to twist and turn.
