Serratus anterior
The muscle that holds your shoulder blade against your ribcage, and rotates it so you can reach overhead.
- Type
- Muscle
- Region
- Shoulder
- Standard name
- m. serratus anterior
- Origin
- Outer surfaces of the upper eight or nine ribs
- Insertion
- Medial border of the scapula, on its costal surface
- Actions
- scapular protractionscapular upward rotationscapular stabilisation
- Verify
- TA2 2307 TA98 A04.4.01.008
What it is
A broad sheet wrapping around the side of the ribcage, from the ribs to the inner edge of the scapula — passing between the shoulder blade and the ribs. Its origin is a row of finger-like slips along the ribs, which is where the name comes from: serratus, serrated, like a saw blade. Those slips are visible on the side of the chest in lean people.
It is sometimes called the boxer's muscle, for its role in punching.
It is supplied by the long thoracic nerve, which runs down the outside of the muscle in an exposed position.
What it does
Two jobs that matter.
It holds the scapula flat against the ribcage. The shoulder blade has no bony joint with the ribs — it floats on muscle. Serratus anterior is the main muscle pulling it inward against the chest wall.
It rotates the scapula upward, turning the socket to face more upward, which is what allows your arm to go overhead. Raising your arm fully is not just a shoulder-joint movement; roughly a third of the range comes from the shoulder blade rotating, and this muscle and trapezius do that together.
If the long thoracic nerve is damaged, the muscle stops holding the blade down and the medial border lifts away from the ribs — scapular winging, the classic and genuinely diagnostic sign.
What loads it
Pushing movements where the shoulder blade travels forward — push-ups, particularly the part past lockout — and overhead reaching against resistance.
What is commonly got wrong about it
Every prominent shoulder blade is "winging". True winging from long thoracic nerve palsy is a specific neurological sign. A shoulder blade that simply sits prominently, common in slim people and in those with less muscle, is not the same thing and is usually of no significance.
"Serratus activation" as a fix for shoulder pain. It is a widely prescribed idea built on a plausible mechanism, and the supporting evidence is modest. It is also, where there is actual pain, a clinical question.
That it is an obscure muscle. It does a third of the work of raising your arm overhead.