Abdominal Oblique Muscles: Functional Anatomy Guide

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The External and Internal Oblique Muscles

The abdominal wall (informally called abs by most bodybuilders) is made up of a very complex mesh of muscles that belong to the group known as the core muscles:

  1. The rectus abdominis, commonly called the abs (the “six-pack” muscle)
  2. The external obliques, on both sides of the rectus abdominis
  3. The internal obliques, under the external obliques
  4. The transversus abdominis, under the obliques

In this post you will find out everything you need to know about the functional anatomy of the external and internal oblique muscles – shape (appearance), function (muscle action), location, insertion, and origin.

Oblique muscles

  • m. obliquus externus abdominis (external oblique muscle)
  • m. obliquus internus abdominis (internal oblique muscle)

external and internal oblique muscles

Muscle Overview: Location, Shape, Function, Insertion, and Origin

Location

The oblique muscles are located on both sides of the abdomen (sides of waist).

  • External obliques. Top layer, closest to the skin, running downwards and forwards.
  • Internal obliques. Located lower near your hip and deeper, below the external obliques (farther inside you) and on top of the transversus abdominis muscles, running downwards and outwards.

Muscle Shape (Appearance)

They are roughly rectangular in shape.

You can imagine all three layers of muscle in the anterolateral (side) abdominal walls:

  • the outermost layer or external oblique;
  • a middle layer or internal oblique, and
  • the innermost layer or transversus abdominis

as a sheetlike muscles.

Function

The obliques are astoundingly versatile muscles. Both sets work together to help you achieve lateral flexion of your trunk, meaning they allow you to bend side-to-side and rotate your mid-body.

Aesthetically, when these muscles are toned, it creates a V-shaped, super-slim waist that highlights the central muscles, the rectus abdominis. Perhaps more importantly, because your obliques wrap around to you back as well, strong obliques will help with proper posture, which helps reduce back pain.

More precisely,

External obliques:

From their position on the sides of your waist, they provide movement by allowing you to bend and twist, and provide stability by helping you resist those same movements.

  • flexion of the torso;
  • bending to same side and turning to opposite side (acting on one side only);
  • lowering the ribs;

Internal obliques:

  • flexion of the torso;
  • bending and turning to same side (acting on one side only);
  • lowering the ribs;

Because the fibers run perpendicular to each other, the ex­ternal and internal oblique muscles alternate duties when you twist. For instance, when you twist to the left, you use the external obliques on your left side and the internal obliques on the right side.

The obliques also help you bend and straighten your body to the sides. This time, the internal and external obliques work to­gether on the same side of your body. Thus, when you crunch your torso to the left, the internal and external obliques on the left side pull your ribs closer to your hip. When you straighten your body after it’s bent to one side, the obliques on the pulling side work together, along with your lower-back muscles.

Because the internal obliques originate in the rear of your midsection, they’re also considered postural muscles. That is, they have to contract throughout the day to keep you upright. You can work them anytime you’re sitting or standing by pulling in your waist and straightening your back. In other words, like the TA, the internal obliques contribute compressive forces to help stabilize the spine. Their connective tissues merge with those of the lats to form a belt-like protective mechanism in your lower back.

The internal obliques are mostly made up of slow-twitch muscle fibers. These are endurance-oriented muscles, designed to go long rather than generate a lot of power in a short burst. That’s why the internal obliques are considered especially important for maintaining good posture. They can produce small amounts of force for a long time.

Origin and insertion of the external and internal obliques

External oblique muscles:

  • Origin: ribs (7th or 8th and last)
  • Insertion: iliac crest, inguinal ligament

The external oblique fibers originate on the lower eight ribs and run diagonally to attach along the top of the pelvis.

Internal oblique muscles:

  • Origin: ribs (last 4)
  • Insertion: inguinal ligament, iliac crest, lumbodorsal fascia

The internal oblique fibers run diagonally upward from the lumbar fascia (in the lower back) and pelvis and attach to the cartilage of the eighth, ninth, and tenth ribs.

Put another way, the external oblique fibers run diagonally downward from the middle of the rib cage, while the internal oblique fibers run diagonally upward from the pelvis. The bottommost internal oblique fibers, however, are more horizontal.

Palpation

  • External oblique muscle. Lying on your back with your knees bent and feet flat on the floor, curl up about 20-degrees so that your head and shoulders rise off the floor. Now rotate toward the left. You can palpate the contraction of the right external oblique by placing your fingertips below the ribs and about 4 inches (10 centimeters) lateral to the navel (umbilicus).
  • Internal oblique muscle. Because the obliques and transverse abdominis are thin layers of muscle running just superficial or deep to one another, their individual actions cannot be well differentiated. However, when one performs the curl-up with rotation to the left (just described for palpating the external oblique), the ten­sion palpated on the left side of the abdomen, just medial to the front of the crest of the pelvis, is in part due to contraction of the left internal oblique.

Exercises for strengthening external and internal oblique muscles

Exercises for strengthening external and internal oblique muscles

The transverse and oblique abdominal muscles form an excellent natural girdle, compressing the abdomen, but they are normally relatively untrained. If you need to choose which part of the abdomen to train first, start with the external and internal obliques, then move onto exercises for the rectus abdominis.

Both the internal and external obliques are best targeted by exercises that flex the spine laterally to the left and right, such as oblique crunches. They also are targeted with exercises that involve flexing the spine forward and rotating it to the left or right, such as with crossover crunches.

However, obliques are only desirable if you have a small waist. If you do not, you will ruin your taper by increasing their size.

Unless you are involved in a strength sport, do not use too heavy a weight when working your obliques. Light weights and long sets will help you eliminate the fat that easily accumulates in this area.

List of the most important exercises that build external and internal oblique muscles:

Closing thoughts

The external and internal oblique muscles are located on either side of the rectus abdominis. They are responsible for rotation and lateral flexion of the trunk. They also assist in trunk flexion and stabilization. Good strength and flexibility in these muscles will make you more agile and able to react swiftly and effectively throughout your daily life. Oblique workouts will include crunches, side twists and leg lifts to hit the muscles in a variety of ways are really getting them toned.

About Author

Hey! My name is Kruno, and I'm the owner and author of Bodybuilding Wizard. I started this website back in late 2014, and it has been my pet project ever since. My goal is to help you learn proper weight training and nutrition principles so that you can get strong and build the physique of your dreams!

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