Middle TrapeziusTransverse Part of Trapezius

backPars transversa musculi trapezii

The middle trapezius runs horizontally from the spine to the shoulder blade and pulls the shoulder blades together. It is the muscle doing the last few inches of every row.

Middle Trapezius highlighted on an anatomical figure, from behind.
Where it sits, from behind.

These fibres run more or less straight across from the upper spine outward to the ridge on the back of the shoulder blade. Because the line of pull is horizontal, their action is simple: they pull the shoulder blade toward the spine. Squeeze your shoulder blades together right now and the middle trapezius is what you are contracting.

That movement — retraction — is the finishing half of every rowing exercise. The first part of a row is the arm travelling backward, which belongs to the lat and the rear deltoid. The last part, where the shoulder blades draw together and the chest opens, belongs here and to the rhomboids underneath.

It also has a constant background job. Whenever you pull anything, the shoulder blade needs something holding it in place for the arm muscles to pull against. The middle trapezius is a large part of that anchor, which is why it is working even in movements where retraction is not the point.

The middle trapezius and the rhomboids do very nearly the same thing and sit on top of each other, the trapezius superficial and the rhomboids beneath. The practical difference is the angle: the middle trapezius pulls straight in, while the rhomboids pull in and slightly up, tilting the shoulder socket downward as they go.

Training notes

This is the part of the back that separates people who row from people who pull. If a row is finished when the elbow is behind the torso, the middle trapezius has barely been asked to do anything; the last two or three inches, where the shoulder blades come together, is the entire point for this muscle.

Horizontal pulling is what trains it, and the angle matters. Rows with the elbows out wide, toward shoulder height, put more work through the middle trapezius and rear deltoid; rows with the elbows tucked in tight to the ribs shift the emphasis toward the lat. A back program benefits from having both.

Face pulls and band pull-aparts are the lightest and most repeatable ways to train it, and they are worth their reputation. They are also easy to do badly: if the hands finish in front of the shoulders rather than beside the head, the shoulder blades never retracted and the set trained nothing much.

It is one of the most reliably under-trained muscles in the body, for the simple reason that no part of ordinary daily life pulls the shoulder blades backward, while a great deal of it pushes them forward.

Anatomy

Origin
  • Spinous processes of the seventh cervical to third thoracic vertebrae
Insertion
  • Medial acromion and the upper crest of the spine of the scapula
Actions
  • Retracts the scapula, drawing it straight in toward the spine
  • Holds the scapula steady against the ribcage during any pulling movement
Innervation
Accessory nerve (CN XI), with sensory fibres from C3–C4

Exercises

Antagonists

Synergists