The Rectus Abdominis and Friends: An Intro to the Ab Muscles

When people think of working out at the gym, chances are that they imagine doing planks, crunches, and sit-ups. Why? Core work is a central component of fitness because building strong abdominal muscles helps with balance and stabilizes the spine, improving posture and aiding in both sports activities and the simplest of everyday movements. If you’ve ever been sore after a tough workout, or if you’ve felt the pain of recovering from abdominal surgery, you’ll know just how active your abs are on a daily basis—it’s hard not to engage them.

So let’s take a couple of minutes and talk about this “core” group of muscles!


Transversus Abdominis

The transversus abdominis muscles are the deepest of the ab muscles, and their job is to tense the abdominal wall, compress abdominal viscera (the internal organs of the abdomen), and stabilize the pelvis and lumbar spine. One transversus abdominis muscle wraps around each side of the abdomen.

ab-muscles-transversus-abdominis-2Image from Muscle Premium

See the “holes” towards the bottom of each transversus abdominis? Each head of the rectus abdominis passes through one of them on its way from the pubis to the xiphoid process and ribs (you’ll see how in the next section).

Origin(s)

- Inguinal ligament
- Iliac crest
- Thoracolumbar fascia
- Inner surface of the cartilage of lower six ribs

Insertion Point(s)

- (Forms aponeurosis)
- Pubis
- Xiphoid process
- Linea alba

Innervation

- T07–T12 spinal nerves
- Iliohypogastric and ilioinguinal nerves (L01)

Blood Supply

Subcostal arteries


Rectus Abdominis

The rectus abdominis muscles are a pair of long muscles that run vertically up the front of the abdomen, stretching from the pubis to the xiphoid process. They compress the viscera and tense the abdominal wall.

You’ll notice in the picture below that the lower part of the rectus abdominis rests underneath the transversus abdominis, and the upper part rests on top.

ab-muscles-rectus-abdominisImage from Muscle Premium

As one of the primary movers in spine flexion, the rectus abdominis also helps to flex the vertebral column and bring the pelvis forward. The internal and external obliques are the other primary movers in spine flexion.

ab-muscles-motion-spine-flexion-gifVideo footage from Muscle Premium

Origin(s)

- Pubis
- Pubic symphysis

Insertion Point(s)

- Xiphoid process
- Fifth, sixth, and seventh ribs

Innervation

T07–T12 spinal nerves

Blood Supply

Superior and inferior epigastric arteries


Did you know that the rectus abdominis is responsible for the appearance of “six-pack” abs? The linea alba vertically separates the right and left rectus abdominis muscles, and bands of tissue divide each one into distinct segments.

The rectus abdominis is held within the rectus sheath, which is formed from the aponeuroses  (sheets of connective tissue) of the transversus abdominis and the internal and external obliques.

ab-muscles-rectus-sheathImage from Muscle Premium


Internal Obliques

The internal obliques are located between the transversus abdominis and the external obliques. When both internal obliques work together, they join the other abdominal muscles in compressing the abdominal viscera. They also help with spinal flexion. When working individually, the internal oblique muscles are principal movers in the rotation and lateral flexion of the spine.

ab-muscles-internal-oblique

ab-muscles-motion-spine-rotation-gifImage and video footage from Muscle Premium

Origin(s)

- Inguinal ligament
- Iliac crest
- Thoracolumbar fascia

Insertion Point(s)

- (Forms aponeurosis)
- Pubis
- Inferior border of lower three or four ribs
- Linea alba

Innervation

- T08–T12 spinal nerves
- Iliohypogastric and ilioinguinal nerves (L01)

Blood Supply

- Intercostal arteries
- Subcostal arteries



External Obliques

The external obliques are the outermost abdominal muscles. They are also key participants in spinal flexion and the compression of the viscera. Individually, they act alongside the internal obliques in lateral flexion and spinal rotation.

ab-muscles-external-oblique

ab-muscles-motion-spine-lateral-flexion-gifImage and video footage from Muscle Premium. 

Origin(s)

- Sternum
- External surfaces and inferior borders of ribs 5–12

Insertion Point(s)

- (Forms aponeurosis)
- Pubis
- Linea alba
- Iliac crest

Innervation

- T07–T12 spinal nerves
- Iliohypogastric and ilioinguinal nerves (L01)

Blood Supply

- Intercostal arteries
- Subcostal arteries
- Deep circumflex iliac arteries



Pyramidalis

The pyramidalis muscles are small muscles that sit in the lower abdominal wall within the rectus sheath. Some people have pyramidalis muscles on both sides, some only have one, and some don’t have any at all. When present, the pyramidalis assists with abdominal cavity compression.

Origin(s)

- Anterior pubis
- Pubic symphysis

Insertion Point(s)

Linea alba

Innervation

Cutaneous branches (part of the ventral portion) of T12

Blood Supply

Superior and inferior epigastric arteries

 

 

So what’s the take-home message here? First, your abs are constantly doing a lot of work to stabilize your pelvis and regulate the pressure on your abdominal cavity. Each layer, from the transversus abdominis to the external obliques, has its own role to play in keeping you moving with good balance and posture. All in all, they make a pretty killer team. You might even say they’re fABulous.


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