| Latin | Musculus obliquus internus abdominis |
|---|---|
| Origin |
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| Insertion |
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| Action |
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| Nerve | Thoracoabdominal nerves, subcostal nerve, iliohypogastric nerve and ilioinguinal nerve (T7–L1) |
| Name | Latin obliquus, 'slanting', and internus, 'inner' — it lies just inside the external oblique. |
Palpation
- Client supine with a bolster under the knees, or side-lying.
- Place a flat hand on the side of the waist just above the front of the iliac crest.
- The internal oblique lies under the external oblique, so you feel it through that layer; its fibres run upwards and forwards, roughly at right angles to the external oblique.
- Ask the client to turn the trunk slightly towards the side you are palpating (for example, lift the right shoulder towards the left knee while you palpate the left waist); the internal oblique on your side tightens.
The internal oblique is the middle of the three flat muscles of the abdominal wall. It sits between the External oblique (outside) and Transversus abdominis (inside). Its fibres fan upwards and forwards from the hip and lower back, roughly at right angles to those of the external oblique, so the two layers form a criss-cross that supports the waist.
The internal oblique is a same-side rotator: the left internal oblique helps turn the trunk to the left, working with the right external oblique. Because it attaches to the thoracolumbar fascia of the lower back, clients sometimes feel waist tension as a band between the lower ribs and the back of the Iliac crest.
You cannot feel the internal oblique on its own through the external oblique, so treat the waist as a whole with gentle pressure. Broad strokes and kneading are usually comfortable. When you stroke across the whole abdomen, work clockwise (as you look down at the abdomen), following the colon up the client’s right side, across, and down the left side.