Dominic Stone
The rectus abdominis muscle, also known as the abdominal muscle or abs, is a pair of segmented skeletal muscles on the front of a person's abdomen. However, the abs are not just one muscle—there are four distinct muscles that make up the abs, each with its own function. These include the transversus abdominis, the rectus abdominis, and the internal and external obliques. Together, these muscles impact core stability, strength, and posture, and provide other important functions.
| Characteristics | Values |
|---|---|
| Number of muscles | 4 |
| Muscle type | segmented skeletal muscle |
| Muscle name | Rectus abdominis |
| Muscle location | Abdomen |
| Muscle function | Support the trunk, allow movement, hold organs in place, regulate breathing, and protect internal organs |
| Muscle appearance | Visible as a 'six-pack' in people with low body fat |
| Muscle thickness | 10mm in non-athletes, 20mm in athletes |
| Muscle volume | 300cm3 in non-active individuals, 500cm3 in athletes |
| Muscle activation | Activated when balancing on an unstable surface or pulling in the belly button |
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What You'll Learn
The rectus abdominis is the central abdominal muscle
The rectus abdominis is contained in the rectus sheath, which consists of the aponeuroses of the lateral abdominal muscles. It is innervated by thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves. The muscle is supplied with blood from several sources, including the inferior and superior epigastric arteries, as well as segmental contributions from the lower six intercostal arteries.
The rectus abdominis is responsible for flexing the lumbar spine, assisting with breathing and respiration, and helping to keep the internal organs intact. It also plays a role in creating intra-abdominal pressure during activities such as exercising, lifting heavy weights, or parturition (childbirth). This muscle is often associated with the six-pack appearance of a fit abdomen.
In terms of exercises, the rectus abdominis can be targeted by performing crunches, sit-ups, or plank variations. It is important to note that abdominal muscles work together as a unit, so functional fitness exercises that activate multiple abdominal muscles at once are recommended.
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The obliques are the V-shaped muscles on the sides
The internal obliques, on the other hand, are much thinner and smaller than the external obliques. They lie underneath the external obliques and work together with them to allow the trunk to twist and turn. Both types of oblique muscles help with the rotation of the spine.
The obliques are a crucial part of the core, which includes the abdominal muscles and the muscles in the lower back. Strong core muscles are essential for daily activities such as standing, sitting, reaching, and bending. They also contribute to better posture and help prevent injuries and back pain.
To effectively work the oblique muscles, it is recommended to diversify your exercise routine and target different types of abdominal muscles. For example, bicycles are a great way to work the obliques, while crunches target the rectus abdominis. By incorporating various exercises, you can improve your functional fitness and ensure that the muscles work effectively as a unit.
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The transversus abdominis is the deepest muscle layer
The transversus abdominis is the deepest abdominal muscle layer. It is a broad, paired muscular sheet found on the lateral sides of the abdominal wall. It is an important core muscle, and its main roles are to stabilise the trunk, increase spine stability, and maintain internal abdominal pressure and abdominal wall tension.
The transversus abdominis is one of the muscles that make up the core, along with muscles in the back and the other abdominal muscles. The core supports the trunk, allows movement, and holds organs in place by regulating internal abdominal pressure. The core also helps keep the body stable and balanced, and protects the spine.
The transversus abdominis is the deepest-down of all the abdominal muscles. It wraps around the midsection and pulls it in like a corset. It is located underneath the internal obliques and external obliques. The internal obliques are the V-shaped muscles running diagonally down your sides that, along with the external obliques, help you rotate your spine.
The transversus abdominis can be targeted with specific exercises. For example, you can lie on your back with bent knees and feet flat on the floor. Place your fingers on the muscles just below your belly button, and then contract those muscles by pulling them down and away from your fingers. Hold this position for 5 seconds, making sure you continue to breathe. The side plank (side bridge) and regular plank are also great exercises for activating the transversus abdominis indirectly.
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The external obliques are the largest abdominal muscles
The rectus abdominis muscle, commonly known as the "abdominal muscle" or "abs", is a pair of segmented skeletal muscles on the front of a person's abdomen. There are five main abdominal muscles, and together with the back muscles, they make up the core muscles. The external obliques are the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. They 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. The external obliques are V-shaped muscles running diagonally down your sides that, along with the internal obliques underneath them, help you rotate your spine. They are the broad, thin, and irregularly quadrilateral muscular portion occupying the side, with their aponeurosis occupying the anterior wall of the abdomen.
The external obliques are the largest and most superficial of the lateral abdominal muscles. They lie beneath the thoracic and abdominal skin, covering the internal abdominal oblique and anterior halves of the ribs and intercostal muscles. The superior, medial, and inferior margins of the muscle relate to their respective attachment points, while the posterior margin is free. The external obliques are innervated by the anterior rami of the thoracic spinal nerves T7-T12. The muscle receives sensory innervation from the lumbar plexus, via the iliohypogastric nerve (L1). The upper two-thirds of the external obliques are supplied with blood by the branches of the lower posterior intercostal and subcostal arteries, while the deep circumflex iliac artery supplies the inferior third of the muscle.
The external obliques have a variety of functions depending on whether they contract unilaterally or bilaterally. When acting unilaterally and in synergy with the internal abdominal oblique, they rotate the trunk to the opposite side. Working together with the abdominal and back muscles, they contribute to the lateral flexion of the trunk on the same side. The external obliques function to pull the chest downwards and compress the abdominal cavity, increasing intra-abdominal pressure. They also perform ipsilateral (same-side) side-bending and contralateral (opposite-side) rotation: the right external oblique would side-bend to the right and rotate to the left, and vice versa.
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The internal obliques are underneath the external obliques
The rectus abdominis muscle, commonly known as the "abdominal muscle" or "abs", is a pair of segmented skeletal muscles that extend along the whole length of the front of the abdomen. The abdominal muscles are made up of four muscle groups: the external obliques, the internal obliques, the rectus abdominis, and the transversus abdominis.
The external obliques are the outermost abdominal muscles, extending from the lower half of the ribs down to the pelvis. They are broad, thin, and irregularly quadrilateral, with the muscular portion occupying the side and the aponeurosis occupying the anterior wall of the abdomen. The external obliques function to pull the chest downwards and compress the abdominal cavity, increasing intra-abdominal pressure. They also perform side-bending and rotation: the right external oblique bends to the right and rotates to the left, and vice versa.
The transversus abdominis is the deepest of the abdominal muscles, wrapping around the midsection like a corset.
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Frequently asked questions
No, there are four separate muscles that contribute to your overall abdominal development.
The four main abdominal muscle groups are the transversus abdominis, rectus abdominis, external obliques, and internal obliques.
The transversus abdominis is the deepest muscle layer and its main roles are to stabilise the trunk and maintain internal abdominal pressure.
The rectus abdominis is a pair of segmented skeletal muscles on the ventral aspect of a person's abdomen. It is the muscle responsible for the six-pack look.
The internal and external obliques help rotate the spine and allow the trunk to twist.
