ABDOMEN

GENERAL INFORMATION

The abdomen is the region between the chest and pelvis that houses vital organs such as the stomach, liver, intestines and kidneys. It plays a crucial role in digestion, respiration and protecting internal organs. The abdominal muscles also support posture, movement and core stabilisation.

ORIGIN

The muscles of the abdomen originate from different points along the pelvis, ribs and spine:

• Rectus Abdominis: Originates from the pubic crest and pubic symphysis.
• External Oblique: Originates from the outer surfaces of the lower eight ribs.
• Internal Oblique: Originates from the inguinal ligament, iliac crest and thoracolumbar fascia.
• Transversus Abdominis: Originates from the iliac crest, inguinal ligament and lower six ribs.

INSERTION POINT

The muscles of the abdomen insert into various structures to support movement and posture:

• Rectus Abdominis: Inserts into the sternum’s xiphoid process and ribs’ costal cartilages 5–7.
• External Oblique: Inserts into the linea alba, pubic tubercle and anterior half of the iliac crest.
• Internal Oblique: Inserts into the linea alba and ribs 10–12.
• Transversus Abdominis: Inserts into the linea alba, pubic crest and pectineal line of the pelvis.

MAJOR ARTERIES

The abdomen receives its blood supply from major arteries, including:

• Superior epigastric artery: Provides blood to the upper portion of the rectus abdominis and anterior abdominal wall.
• Inferior epigastric artery: Supplies blood to the lower part of the rectus abdominis and lower abdominal muscles.
• Lumbar arteries: Supply blood to the posterior abdominal wall and the lower back muscles.

NEURAL INNERVATION

The following nerves innervate the abdominal muscles:

• Thoracoabdominal nerves: These nerves, derived from the lower six thoracic spinal nerves, provide motor innervation to the rectus abdominis, external and internal obliques and transversus abdominis.
• Iliohypogastric nerve: Provides sensory and motor innervation to the lower abdomen and hip region.
• Ilioinguinal nerve: It innervates the lower abdomen muscles and provides sensation to the groin and inner thigh.

TRIGGER POINT

Trigger points can develop in the abdominal muscles, especially the rectus abdominis and obliques, causing pain and discomfort. These trigger points often result from poor posture, overuse or injury.

CONCENTRIC FUNCTION

The concentric functions of the abdominal muscles are critical in movements like:

• Rectus Abdominis: Contracts to flex the spine, aiding in movements like crunches or bending forward.
• External Oblique: Assists in rotating the trunk and flexing the spine.
• Internal Oblique: Helps rotate and laterally flex the trunk, contributing to core stability.
• Transversus Abdominis: Acts to compress the abdominal contents, stabilising the core and supporting posture.

ECCENTRIC FUNCTION

The abdominal muscles play an essential role in eccentric movements by controlling the extension of the spine:

• Rectus Abdominis: Eccentrically controls the lowering of the torso during sit-ups or when bending backwards.
• External and Internal Obliques: Control the deceleration of trunk rotation or lateral flexion during dynamic movements.
• Transversus Abdominis: Helps stabilise the core during the controlled relaxation of abdominal tension.

ISOMETRIC FUNCTION

The abdominal muscles engage isometrically to stabilise the core during static postures:

• Rectus Abdominis: Contracts isometrically to maintain posture and core stability during activities like planking.
• Obliques: Engage to stabilise the torso during isometric holds such as side planks.
• Transversus Abdominis: Helps maintain abdominal tension and support during static exercises or heavy lifting.

RELATED MUSCLES SCIENTIFIC NAMES

• Rectus Abdominis: The “six-pack” muscle supports trunk flexion and stabilises the core.
• External Oblique: Involved in trunk rotation and lateral flexion, providing side-to-side movement and core stability.
• Internal Oblique: Supports trunk rotation and side bending, working with the external oblique for core strength.
• Transversus Abdominis: The deepest abdominal muscle helps compress the abdomen and stabilise the core during movement.
• Psoas Major: Located deep in the abdomen, it plays a role in hip flexion and stabilising the lumbar spine.

ANTAGONIST

• Erector Spinae: Opposes the rectus abdominis by extending the spine during movements like backbends or standing upright.
• Quadratus Lumborum: Works against the obliques by assisting in lateral flexion and stabilising the spine during trunk movements.
• Latissimus Dorsi: Acts as an antagonist during trunk flexion, providing stability and supporting the back during rotational movements.

COMMON INJURIES

• Abdominal Strain: Occurs when the abdominal muscles are overstretched or torn, often during heavy lifting or sudden twisting, causing sharp pain and weakness.
• Hernia: A protrusion of abdominal contents through the muscle wall, often caused by weakness or strain, leading to discomfort and a visible bulge.
• Rectus Diastasis: A separation of the rectus abdominis muscles along the linea alba, commonly occurring during pregnancy or from excessive strain, causing abdominal weakness.
• Oblique Strain: Involves the overstretching or tearing of the oblique muscles, often from sudden twisting movements, resulting in pain along the side of the abdomen.
• Core Muscle Injury: A sports hernia involves damage to the lower abdominal muscles, leading to chronic pain in athletes during intense physical activity.

EXERCISES

• Crunches: Targets the rectus abdominis by flexing the spine, helping build core strength and abdominal definition.
• Russian Twists: Engages the obliques by rotating the torso from side to side while sitting, improving core rotation and stability.
• Planks: Strengthens the entire core by holding a static position, engaging the rectus abdominis, obliques and transversus abdominis.
• Leg Raises: Targets the lower part of the rectus abdominis by lifting the legs while lying on the back, improving core strength and stability.
• Bicycle Crunches: Works the rectus abdominis and obliques by mimicking a pedalling motion, enhancing core rotation and abdominal endurance.

STRETCHES

• Cobra Stretch: Stretches the abdominal muscles by arching the back while lying face down, helping to increase flexibility and relieve tension.
• Side Stretch: Targets the obliques by reaching the arm overhead and leaning to one side, stretching the sides of the abdomen.
• Child’s Pose: Gently stretch the lower back and abdominals by sitting on the heels and extending the arms forward, releasing tension in the core.
• Cat-Cow Stretch: Involves alternating between arching and rounding the spine while on all fours, improving flexibility and relieving abdominal tension.
• Standing Overhead Reach: Stretches the entire core by extending the arms overhead and reaching upward, elongating the abdominal muscles and improving flexibility.