External oblique
The outermost of the flat abdominal muscles, with fibres running the way your fingers point in your pockets.
- Type
- Muscle
- Region
- Trunk
- Standard name
- m. obliquus externus abdominis
- Origin
- Outer surfaces of the fifth to twelfth ribs, interdigitating with serratus anterior and latissimus dorsi
- Insertion
- Iliac crest, pubic tubercle and the linea alba, via a broad aponeurosis
- Actions
- trunk rotationtrunk sidebendingtrunk flexion
- Verify
- TA2 2364 TA98 A04.5.01.008
What it is
The largest and most superficial of the three flat abdominal muscles, forming the outer layer of the side and front of the abdominal wall.
Its fibres run downward and forward, in the direction your fingers point when you put your hands in your front pockets — the standard and genuinely useful mnemonic.
Its origin interlocks with serratus anterior and latissimus dorsi along the ribs, a visible zig-zag in lean people. Towards the midline the muscle becomes a broad flat tendon sheet, an aponeurosis, which contributes to the sheath around rectus abdominis. Its lower border rolls under to form the inguinal ligament.
What it does
Rotates the trunk to the opposite side — the right external oblique turns you to the left. It also side-bends the trunk to its own side and assists in flexing it.
It pairs with the internal oblique on the other side, whose fibres run perpendicular to its own. Rotating your torso is one external oblique and the opposite internal oblique working together — which is why the abdominal wall is built in crossing layers.
With the others it raises intra-abdominal pressure, which is part of how the trunk is stiffened under load.
What loads it
Resisted rotation, anti-rotation work, side bending under load, and single-sided carries — a weight held in one hand loads the opposite side of the abdominal wall continuously.
The side plank loads it hardest, because sideways is the direction nothing else works. The bird dog asks it to resist rotation, and the plank to resist extension.
What is commonly got wrong about it
"Oblique exercises for a smaller waist." Side bends and twists train the muscle. Training a muscle does not reduce the fat over it, and building the abdominal wall does not narrow a waistline — if anything, more muscle is more muscle. The premise is spot reduction and it is false.
That the obliques are one muscle. There are two on each side, running at right angles to one another and doing opposite rotations.
"Core" as a synonym for abdominals. The trunk is stabilised by the abdominal wall, the diaphragm, the pelvic floor and the deep spinal muscles together.