The internal oblique muscle is a key component of the core, contributing to trunk stability and movement. It is one of the three main layers of the abdominal wall. Understanding this muscle helps in comprehending how the body moves and maintains central stability.
Precise Location of the Internal Oblique
The internal oblique muscle lies in the middle layer of the lateral abdominal wall. It is positioned beneath the more superficial external oblique muscle and rests above the deepest abdominal muscle, the transversus abdominis.
Its fibers originate from several points: the thoracolumbar fascia, a strong connective tissue in the lower back; the front two-thirds of the iliac crest, the curved upper border of the hip bone; and the lateral half of the inguinal ligament, a band extending from the hip bone to the pubic bone. From these origins, the fibers ascend forward and medially.
The internal oblique inserts into the lower three or four ribs, specifically their cartilages, contributing to the rib cage’s stability. Many of its fibers also merge with the rectus sheath, a strong fibrous enclosure around the rectus abdominis muscle, before inserting into the pubic crest and the pectineal line of the pubic bone. The direction of its muscle fibers runs opposite to those of the external oblique, resembling placing hands into pockets.
What the Internal Oblique Does
The internal oblique muscle performs several actions affecting the trunk. When contracting on one side, it contributes to trunk rotation to the same side (ipsilateral rotation). For example, if the right internal oblique contracts, the trunk rotates to the right. It also assists in lateral flexion, which is bending the trunk sideways towards the same side of the contracting muscle.
Beyond movement, the internal oblique plays a role in abdominal compression. This action increases intra-abdominal pressure, a mechanism that supports the spine during activities like lifting heavy objects. It also aids in forced exhalation, helping to expel air from the lungs more forcefully. This muscle is also active during actions such as coughing, sneezing, and defecation.
Identifying Your Internal Oblique
Feeling the internal oblique can help in understanding its location and function. To sense its activation, place your fingers gently on your lower abdomen, just inside the bony prominence of your hip bone. From this position, perform a subtle twist of your trunk to the same side where your fingers are placed. You may feel a slight hardening or contraction of the muscle beneath your fingertips.
Another method involves a gentle cough while your fingers are in the same position. The internal oblique, along with other abdominal muscles, contracts to create the pressure needed for a cough. You should feel a distinct tightening in that area. This tactile feedback helps engage the muscle more effectively for core stability and movement during exercise or daily activities.