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The abdominal muscles are a group of muscles that surround the trunk, between the rib cage and pelvis, and keep the abdominal organs safe. They support the trunk, allow movement, and hold organs in place by regulating internal abdominal pressure. The deep abdominal muscles, together with the back muscles, make up the core muscles, which help keep the body stable and balanced and protect the spine. The abdominal muscles are also needed to maintain posture and support the spine. The transversus abdominis, rectus abdominis, external oblique, internal oblique, and pyramidalis muscles are the five muscles that surround the abdomen.
| Characteristics | Values |
|---|---|
| Location | Between the ribs and the pelvis |
| Function | Support the trunk, allow movement, hold organs in place, and maintain uniform pressure inside the abdomen |
| Composition | Four main muscle groups: transversus abdominis, rectus abdominis, external oblique muscles, and internal oblique muscles |
| Core muscles | Include deep abdominal muscles and back muscles, such as multifidus |
| Exercises | Abdominal draw-in, stomach vacuums, bird dogs, dead bugs, hollow body holds, planks, wipers, Pilates |
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What You'll Learn
Transversus abdominis
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. The transversus abdominis muscle is important for maintaining normal abdominal tension and increasing intra-abdominal pressure. It helps to stabilise the trunk and maintain internal abdominal pressure.
The transversus abdominis arises from the lower six ribs and the hip bone and attaches to the pubic crest. It is innervated by the lower intercostal nerves (thoracoabdominal, nerve roots T7-T11), as well as the iliohypogastric nerve and the ilioinguinal nerve. 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 transversus abdominis fibres course horizontally over the lateral abdominal wall towards the midline, oriented perpendicular to the linea alba.
The transversus abdominis is also known as the transverse abdominis, transversalis muscle, and transverse abdominal muscle (TVA). The transverse abdominal muscle is the innermost of the flat muscles of the abdomen. It serves to compress and retain the contents of the abdomen, as well as assist in exhalation. The transverse abdominal helps to compress the ribs and viscera, providing thoracic and pelvic stability. It can contract during the exhalation phase of respiration to force air out of the thorax.
The TVA is vital to back and core health and has the effect of pulling in what would otherwise be a protruding abdomen, hence its nickname, the "corset muscle". Training the TVA is key to achieving a "flat" belly, as it helps to brace the human core. The TVA works in tandem with the segmental stabilizers of the spine, such as the multifidi.
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Rectus abdominis
The rectus abdominis is a long, flat muscle that extends along the whole length of the front of the abdomen. It is commonly referred to as the "six-pack" and is responsible for the bumps and ridges that appear on the abdomen when it contracts. The rectus abdominis is the top layer of the abdominal muscles and is separated from its fellow on the opposite side by the linea alba, a connective tissue.
The rectus abdominis is attached to the pubic bone at the front of the pelvis and to the 5th, 6th, and 7th ribs. It acts to flex the spinal column, tense the anterior wall of the abdomen, and assist in compressing the contents of the abdomen. This muscle is innervated by the thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves. The sensory supply comes from the 7-12 thoracic nerves.
The rectus abdominis is an important postural muscle, responsible for flexing the lumbar spine, as seen in a crunch or leg-hip raise. It also assists with breathing and plays a role in respiration during forceful exhalation, such as after exercise.
The rectus abdominis is part of the core muscles, which act like a natural weight belt to protect the lower back from injury. These muscles help to stabilise the trunk and maintain internal abdominal pressure. Weak core muscles can lead to spinal problems.
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External oblique muscles
The external oblique muscles are the outermost abdominal muscles, also known as the obliquus externus abdominis. They are located on the lateral sides of the abdominal wall, extending from the lower half of the ribs around and down to the pelvis. These muscles cover the sides of the abdominal area, sitting on the top surface of the abdomen, right below the subcutaneous fat and skin. They are the largest and most superficial of the flat abdominal wall muscles.
The external oblique muscles work together with the internal oblique muscles, which lie underneath them on each side of the trunk. They originate from the external surfaces of the lower eight ribs and attach to the hip bone. These muscles help you turn your trunk from side to side, allowing the trunk to twist, but to the opposite side of whichever external oblique is contracting. For example, the right external oblique contracts to turn the body to the left.
The external oblique muscles are paired muscles, with one on each side of the body. They contribute to a variety of trunk movements, including flexion and contralateral rotation of the torso. They also help pull the chest downwards, which compresses the abdominal cavity. The upper two-thirds of the external oblique muscles are supplied by the lower intercostal nerves T7-T11 and the subcostal nerve T12, while the lower third is supplied by the iliohypogastric L1 from the lumbar plexus.
The external oblique muscles receive blood supply from the branches of the lower posterior intercostal and subcostal arteries, which supply the upper two-thirds of the muscle, while the deep circumflex iliac artery supplies the lower third. These muscles have a variety of functions, depending on whether they contract unilaterally or bilaterally. When contracting unilaterally, they work with the contralateral internal oblique to rotate the trunk to the opposite side. When working bilaterally with the ipsilateral abdominal and back muscles, they contribute to lateral flexion of the trunk on the same side.
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Internal oblique muscles
The internal oblique muscles, or obliquus internus abdominis, are paired muscles that lie on either side of the abdomen. They are located deeper than the external oblique muscles but outside the transversus abdominis, which is the deepest abdominal muscle. The internal oblique muscles originate on the inguinal ligament, which runs from the anterior iliac spine to the pubic bone, and they also originate on the anterior iliac crest.
The internal oblique muscles enable you to twist and turn your trunk. They work together with the external oblique muscles as synergists to achieve this torsional movement. For example, the right internal oblique and the left external oblique contract as the torso flexes and rotates to bring the left shoulder towards the right hip. The internal oblique muscles also act as an accessory muscle of respiration, helping to reduce the volume of the chest cavity during exhalation. When the internal oblique muscles contract, they compress the organs of the abdomen, pushing them upwards into the diaphragm, which then intrudes back into the chest cavity, reducing the volume of the lungs and producing an exhalation.
The internal oblique muscles are one of the three layers that create our abdominal walls, along with the external oblique muscles and the transverse abdominis muscle. The internal oblique muscles are a broad, thin muscular sheet found on the lateral side of the abdomen. They have a slanting direction, with fibres that reach across the body.
The internal oblique muscles are important for maintaining normal abdominal tension and increasing intra-abdominal pressure. Along with the other abdominal muscles, they help to hold the abdominal organs in place.
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Multifidus
The multifidus muscle is a deep back muscle that runs along the spine and is involved in moving the trunk. It is an important stabilizer of the lumbar spine and functions together with the transversus abdominis and pelvic floor muscles for spine stability. The multifidus muscle is probably active in all anti-gravity activities. It stabilizes the vertebrae as the spine moves, allowing each spinal bone (vertebra) to work individually and more efficiently. This helps protect against spinal deterioration and the onset of arthritis.
The multifidus muscle is situated on both sides of the lumbar spine and provides stability and strength to the lower back. Any weakness in the multifidus muscle can lead to spinal instability, vertebral compression, and back pain. Exercise targeting the multifidus muscle and other core muscles can help prevent back pain and protect against arthritis and other problems affecting the lower back.
There are several exercises that can help strengthen the multifidus muscle. One example is the pelvic tilt exercise, which involves lying on your back with bent knees and flat feet. You then flatten your lower back against the floor by contracting your abdominal muscles and hold this position for 5-10 seconds before releasing. This exercise can be repeated 10-15 times. Another exercise is the bridge, which also involves lying on your back with bent knees and flat feet. In this exercise, you lift your hips towards the ceiling while squeezing your glutes and tightening your core.
Other exercises that can help strengthen the multifidus muscle include the dumbbell bench exercise, the deep multifidus contraction, the Superman exercise, and the forward bend. It is important to consult a qualified healthcare professional or fitness instructor before beginning any new exercise program, especially if you have any pre-existing conditions or injuries.
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Frequently asked questions
The abdominal muscles are the muscles forming the abdominal walls, the abdomen being the portion of the trunk connecting the thorax and pelvis. The abdominal muscles support the trunk, allow movement, and hold organs in place.
The deep abdominal muscles, together with muscles in the back, make up your core muscles. Your core muscles help keep your body stable and balanced, and protect your spine.
Some exercises that target the transverse abdominis include stomach vacuums, bird dogs, dead bugs, hollow body holds, planks, wipers, and the Pilates one-hundred. Stability exercises, such as isometric contractions, can help increase core stability.
Strategies to prevent abdominal muscle strain include regular stretching, warming up before exercise and cooling down afterward, and maintaining good form while playing sports.
