What is rectus abdominis?

Rectus Abdominis Muscle: Anatomy, Function, Assessment, Exercises, and Related Conditions

Introduction

The Rectus Abdominis is one of the most recognizable muscles of the human body, often referred to as the “six-pack” muscle. It is a long, flat muscle that extends vertically along the front of the abdomen. While popular in fitness culture for its aesthetic appeal, its clinical importance is far greater. The Rectus Abdominis plays a vital role in trunk movement, core stabilization, and respiratory function. It also assists in protecting internal organs and maintaining intra-abdominal pressure.

Understanding the structure and function of this muscle is essential for professionals in physiotherapy, sports science, and medicine.

Anatomy of the Rectus Abdominis

Origin

The Rectus Abdominis originates from the pubic symphysis and pubic crest of the pelvis.

Insertion

It inserts superiorly into the xiphoid process of the sternum and the costal cartilages of ribs 5 to 7.

Nerve Supply

The muscle is innervated by the lower six thoracoabdominal nerves (T7–T11) and the subcostal nerve (T12). These nerves are branches of the anterior rami of the spinal nerves.

Blood Supply

Supplied primarily by the superior epigastric artery (from the internal thoracic artery) and the inferior epigastric artery (from the external iliac artery).

Function of the Rectus Abdominis

The primary functions include:

  • Trunk flexion: It bends the spine forward, such as during a sit-up.

  • Pelvic stabilization: Helps control anterior pelvic tilt.

  • Maintaining intra-abdominal pressure: Supports the abdominal viscera during activities like coughing, sneezing, defecation, and childbirth.

  • Assisting forced expiration: It contracts to help push air out of the lungs during exertion.

Assessment of the Rectus Abdominis

1. Palpation

  • Patient position: Supine lying, knees bent, arms by the side.

  • Procedure: Ask the patient to raise their head and shoulders slightly off the table. The Rectus Abdominis will become prominent and can be palpated along the midline.

2. Muscle Power Test

  • Grade 0–5 system:

    • Grade 0: No visible or palpable contraction.

    • Grade 1: Flicker of contraction.

    • Grade 2: Able to move the trunk with arms extended (gravity eliminated).

    • Grade 3: Partial sit-up with arms extended forward.

    • Grade 4: Arms crossed over chest and completes sit-up.

    • Grade 5: Arms behind head and completes sit-up with ease.

3. Muscle Length Test

The Rectus Abdominis is a postural muscle, and its length is typically assessed via spinal extension:

  • Patient position: Supine at the edge of the table, legs hanging, with opposite knee to chest.

  • Procedure: Extend the spine while maintaining hip position. Excessive tightness restricts spinal extension.

Exercises for Rectus Abdominis

1. Basic Crunches

  • Position: Supine, knees bent, hands behind head or across chest.

  • Procedure: Engage core and lift shoulders off the floor while keeping the lower back on the mat.

  • Repetitions: 3 sets of 10–15 reps.

2. Reverse Crunch

  • Position: Supine, knees bent, arms at the sides.

  • Procedure: Lift the pelvis off the ground by curling it toward the chest using the lower abs.

3. Plank Hold

  • Position: Prone on elbows and toes.

  • Procedure: Engage the Rectus Abdominis to keep the spine neutral.

  • Hold: 20–60 seconds, 3–4 repetitions.

4. Leg Raises

  • Position: Supine, arms by the sides.

  • Procedure: Raise both legs to 90 degrees and slowly lower them down without touching the ground.

5. Physiotherapy Ball Rollout

  • Position: Kneeling, forearms on a Swiss ball.

  • Procedure: Roll the ball forward slowly, engaging the core to return to starting position.

Trigger Points in Rectus Abdominis

Trigger points in the Rectus Abdominis may present as:

  • Deep, aching abdominal pain.

  • Referred pain to the mid-lower back, lower chest, or anterior hip region.

  • Symptoms mimicking gastrointestinal issues or urinary discomfort.

Common Causes of Trigger Points

  • Chronic poor posture

  • Weak core muscles

  • Abdominal trauma or surgery

  • Prolonged sitting

Management

  • Dry needling

  • Myofascial release

  • Stretching exercises

  • Postural correction

Common Injuries and Clinical Relevance

1. Muscle Strain

Often occurs during activities that involve excessive trunk flexion or twisting.

Symptoms:

  • Sharp pain in the abdominal region

  • Bruising

  • Swelling

  • Muscle tightness

Management:

  • Rest, ice, compression, elevation (RICE)

  • Gradual strengthening

2. Diastasis Recti

Separation of the Rectus Abdominis muscles along the linea alba, commonly seen during or after pregnancy.

Symptoms:

  • Midline abdominal bulge

  • Weak core

  • Back pain

Management:

  • Gentle core stabilization exercises

  • Physiotherapy supervision

3. Rectus Sheath Hematoma

A rare but serious condition involving bleeding into the rectus sheath.

Symptoms:

  • Acute abdominal pain

  • Palpable mass

  • Bruising

Requires: Immediate medical attention

FAQs about Rectus Abdominis

Q1: Can everyone get visible six-pack abs?

Not necessarily. Genetics, body fat percentage, and muscle thickness all play a role. Strengthening the Rectus Abdominis is essential, but so is overall fat loss through diet and cardio.

Q2: What’s the difference between core and abs?

The Rectus Abdominis is just one part of the core. The core also includes the obliques, transverse abdominis, pelvic floor muscles, and lower back muscles.

Q3: Are sit-ups harmful to the spine?

If done improperly or in excess, sit-ups can place strain on the lumbar spine. Alternative core exercises like planks are often safer.

Q4: How long does it take to strengthen the Rectus Abdominis?

Noticeable improvements may take 6–8 weeks with consistent training, depending on the individual's baseline strength and training intensity.

References

  1. Moore, K. L., Dalley, A. F., & Agur, A. M. R. Clinically Oriented Anatomy (7th Edition).
    https://shop.lww.com/Clinically-Oriented-Anatomy/p/9781451119459

  2. Travell, J. G., & Simons, D. G. Myofascial Pain and Dysfunction: The Trigger Point Manual, Vol. 1.
    https://www.wolterskluwer.com/en/solutions/ovid/myofascial-pain-and-dysfunction-the-trigger-point-manual-vol-1-1498

  3. Physiopedia. Rectus Abdominis.
    https://www.physio-pedia.com/Rectus_Abdominis

  4. Kenhub. Anatomy of the Rectus Abdominis.
    https://www.kenhub.com/en/library/anatomy/rectus-abdominis-muscle

  5. TeachMeAnatomy. Rectus Abdominis.
    https://teachmeanatomy.info/abdomen/muscles/rectus-abdominis/

  6. PubMed – National Library of Medicine. Rectus Abdominis in Clinical Practice.
    https://pubmed.ncbi.nlm.nih.gov/


Location: Pakistan

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