SerratusSerratus Anterior

chestMusculus serratus anterior

The serratus anterior is the fan of finger-like slips along the side of the ribcage that holds your shoulder blade against your ribs and swings it around as you reach overhead. Without it, the arm cannot get above the head.

Look at the side of a lean torso below the armpit and you can see the serratus as a row of angled ridges over the upper ribs — the pattern that gave it its name, from the Latin for a saw. It wraps from those ribs around the side of the chest, passes underneath the shoulder blade, and attaches all along the shoulder blade's inner edge.

Its first job is unglamorous and constant: it holds the shoulder blade flat against the ribcage. The scapula is not fixed to the torso by a joint the way most bones are — it floats on muscle — and the serratus is the strap that keeps it there. Push your hands hard into a wall and you can feel it fire along your ribs.

Its second job is what makes it matter for lifting. Raising your arm overhead is not just a shoulder movement; the shoulder blade has to swivel so that the socket turns upward, and the serratus, working with the upper and lower trapezius, is what turns it. Roughly a third of the total range of raising your arm comes from the shoulder blade rather than the shoulder joint.

When the serratus is not doing its job, the inner edge of the shoulder blade lifts away from the ribcage instead of staying flat — the appearance known as a winged scapula. This is a mechanical description, not a self-diagnosis: winging has several possible causes and is a question for a professional rather than for a website.

Training notes

The serratus is trained by reaching, not by pulling. The distinguishing cue is that the shoulder blade must be allowed to travel forward around the ribs — which is precisely what most lifting advice tells beginners to stop doing. Cues to pin the shoulder blades back and down are useful for keeping a bench press stable and useless for training this muscle.

The two most direct movements are the push-up plus — a normal push-up with an extra few inches of pushing at the top, letting the upper back round forward — and any overhead press taken to full lockout with the arms genuinely finishing over the head rather than in front of it. Both ask for the two things the serratus does: protraction and upward rotation.

It is a muscle worth knowing about mainly because it is the quiet prerequisite for overhead work. When someone cannot press overhead without their lower back arching, an inability to rotate the shoulder blade far enough is one of the common reasons the arms cannot travel further back.

Anatomy

Origin
  • Outer surfaces of the first to eighth or ninth ribs, by a row of fleshy slips
Insertion
  • Medial border of the scapula on its costal surface, with most fibres converging on the inferior angle
Actions
  • Protracts the scapula, drawing it forward around the ribcage
  • Rotates the scapula upward so the arm can reach overhead
  • Holds the medial border of the scapula against the ribcage
Innervation
Long thoracic nerve (C5–C7)

Serratus anterior wraps the side of the thorax. It arises by a series of fleshy digitations from the outer surfaces of the upper eight or nine ribs — the saw-toothed pattern the name refers to — then passes backward beneath the scapula to attach along the whole length of its medial border, on the surface facing the ribs.

The distribution of muscle along that border is uneven and this determines what it does. The lower fibres, the largest part, converge on the inferior angle; when they shorten they swing the bottom corner of the scapula forward and around the ribcage, which is upward rotation. The upper fibres pull the scapula forward more directly, which is protraction.

It works as a pair with the trapezius. Serratus anterior and the upper and lower trapezius attach to different corners of the scapula and together produce the upward rotation that accompanies raising the arm — roughly sixty degrees of scapular rotation across a full overhead reach, contributing about a third of the total range.

Its supply by the long thoracic nerve is clinically prominent: the nerve runs superficially down the side of the chest, and loss of its function produces medial scapular winging, in which the inner border of the shoulder blade lifts away from the ribcage. That is a description of a sign, not guidance — winging has several causes and belongs to a clinician.

Under load

It is loaded by movements that let the scapula travel forward and rotate upward. Push-ups taken past the normal lockout into scapular protraction, overhead pressing with the arms finishing genuinely vertical, and any weighted reach forward all recruit it.

Cues to retract and depress the scapulae, useful for stabilising a heavy press, directly oppose what this muscle does. Both are correct in their place; the point is that they are different places.

Its endurance role is larger than its movement role. It holds the scapula flat against the ribcage continuously during any load carried in the hands, which is a different demand from the short protraction efforts that most direct exercises train.

Exercises

No exercise in the library names Serratus yet. Nothing has been invented to fill the gap — a false reference costs more than an absent one.

Antagonists

Synergists