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The 5 Main Muscles of Movement.

Anatomy in detail:

2. RECTUS ABDOMINIS

A sketch of a human figure showing the external muscles. Front view. The rectus abdominis muscles are highlighted, extending up the front of the abdomen from pubic symphysis to costal cartilages of the ribs. Like two parallel stacks of panels of muscle, separated by horizontal strips of connective tissue. The linea alba is also labelled, a strip of connective tissue on the body's midline lying between the rectus abdominis muscles.

The left and right rectus abdominis muscles lie parallel to each other, extending from pelvis to chest at front of the abdomen.

rectus ≅ straight

abdominis ≅ abdomen

rectus abdominis keeping it simple

Proximal Attachments Of The Rectus Abdominis.

  • Costal cartilages of the 5th, 6th and 7th ribs (on the medial inferior costal margins).
  • Posterior aspect of xiphoid process of the sternum.
Two images of the rectus abdominis muscles and their attachment sites. Front and back view. Showing the pelvic bones with the pubic symphysis midline at the front from where the rectus abdominis and linea alba originate. The upper attachments of the rectus abdominis are to the outside of the costal cartilage of ribs 5, 6 and 7 so these attachments are covered by muscle on the front view. The costal cartilage and xiphoid process of the sternum are visible on the back view.

Distal Attachment Of The Rectus Abdominis.

  • Pubic symphysis and pubic crest of the pelvis. Home of the clitoris/suspensory ligament of penis.

Sections Of The Rectus Abdominis Muscles.

The rectus abdominis consist of several “panels” of muscle between strips of connective tissue known as tendinous intersections.

These sections are what give the rectus abdominis the “6-pack” look, but the number of panels can vary between individuals e.g. 4, 8, and 10 packs can occur.

Front view of the muscles and connective tissue of the abdomen. On the right side the most external layer of connective tissue, the aponeurosis of the external occipital oblique, has been removed to show the rectus abdominis muscle made up panels of muscle. The left side shows the aponeurosis of the external occipital oblique, with a window cut through to expose the rectus abdominis. Another window is cut through the rectus abdominis to show the deeper aponeurosis. The rectus abdominis muscles running between these aponeuroses in the rectus sheath.

The Rectus Sheaths.

Each rectus abdominis lies within its rectus sheath, a 'tunnel' made from the aponeuroses of the lateral abdominal muscles (the external abdominal oblique, internal abdominal oblique and transversus abdominis) before they merge with the linea alba at the front of the abdomen.

linea alba

The rectus abdominis muscles are the key to feeling the relative positioning of the linea alba, our primary guide for alignment.

Cross section view showing the rectus sheaths containing the rectus abdominis muscles. The rectus sheaths are formed from the aponeuroses of the lateral abdominal muscles on their way to meeting midline to form the linea alba at the front of the abdomen. The rectus abdominis muscles threading through the sheath, like a ribbon in a tunnel.

Cross-section of the anterior abdominal wall.

Rectus Abdominis - Your Base-Line's Central Line.

The rectus abdominis muscles are part of the body's Base-Line, along with the pelvic floor.

Base-Line muscles

human figure from two angles showing the baseline muscles. The pelvic floor, like a basket of muscles. A crescent-shape on midline. The rectus abdominis muscles at the front of the abdomen. The rectus abdominis muscles are the body's central line from pelvis to chest. The body's core pillar of strength to support the movement of the rest of the body when fully activated and elongated.

The rectus abdominis muscles should be 'long and strong', activated and extended to support movement of the rest of the body. When the rectus abdominis are used properly they allow us to stand upright without stress on the spine.

More Information On The Rectus Abdominis:

Narayanan VK, Peter S, Nair AJ. The rectus abdominis muscle in males and females of Keralaa cadaveric study 2017. source

"It has a tendinous origin and a muscular insertion.

It arises by two tendinous heads: Medial head arises from the anterior surface of the pubic symphysis and the lateral head arises from the lateral part of the pubic crest and the pubic tubercle.... The origin was seen to be tendinous and narrow and remained tendinous up to 3 cm from its origin. Pyramidalis muscle when present was seen overlapping this part of rectus abdominis.

The muscle is inserted on the anterior thoracic wall by four fleshy slips that are attached in a horizontal manner to the lower part of the anterior thoracic wall - along a horizontal line passing laterally from the xiphoid process and cutting in that order, the 7th, 6th and 5th costal cartilages.

The paired recti muscles are separated in the median plane by the linea alba.

The muscle is three times as wide superiorly as inferiorly. It is broad and thin superiorly and narrow and thick inferiorly.

An increase in length of 1 to 2 cm in the left rectus abdominis was seen in all the 20 cadavers, which was a striking feature

The rectus abdominis is enclosed in the rectus sheath, which is formed by the aponeuroses of the anterolateral muscles of the anterior abdominal wall.

The muscle usually presents tendinous intersections along its length. ... The absence of tendinous intersections in the foetal specimens could imply that they fully develop after birth, probably after the child becomes ambulant."

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