TrapsTrapezius

back3 musclesMusculus trapezius

The trapezius is the large diamond-shaped muscle covering your upper back and the back of your neck. It has three parts that pull the shoulder blade in three different directions, and only one of them is the shrug.

Traps: its 3 muscles highlighted on an anatomical figure, from behind — Upper Trapezius, Middle Trapezius and Lower Trapezius.
Where the traps sit, from behind.

The trapezius is a single flat muscle spread across the whole upper back. It runs from the base of the skull, down the neck, and along the spine as far as the bottom of the ribcage, and from there its fibres converge outward onto the collarbone and the ridge of the shoulder blade. Both sides together form a diamond, which is where the name comes from.

The reason it is worth thinking of as three muscles rather than one is that its fibres run in three different directions. The upper fibres come down from the neck and pull the shoulder up. The middle fibres run straight across from the spine and pull the shoulder blade in. The lower fibres run upward from the mid back and pull the shoulder blade down. Each part can work on its own, and they routinely oppose one another.

They also cooperate in a way that is worth understanding: when you raise your arm overhead, the upper and lower fibres pull on opposite corners of the shoulder blade at the same time, spinning it so that the socket turns upward. Neither part could do that alone. This is a genuine force couple, and it is the reason overhead pressing trains far more of the trapezius than shrugging does.

In gym vocabulary traps almost always means the upper fibres — the visible slope from neck to shoulder. That is roughly a quarter of the muscle, and the part that needs the least help.

Training notes

The trapezius is the clearest case in the body for training a muscle by its parts rather than as a whole. Shrugs train the top. Rows and face pulls train the middle. Overhead work and movements that pull the shoulder blade down and back train the bottom. A program that does only shrugs has trained a quarter of it and called the job done.

Of the three, the lower fibres are by a distance the most commonly neglected, and they are the ones that matter most for getting the arms comfortably overhead. Anything that finishes with the shoulder blade pulled down and back — a face pull with the elbows high, a prone Y raise, a controlled lat pulldown — is training them.

Upper trap development is a legitimate goal that has acquired an undeserved reputation. Well-developed upper traps are a normal feature of strong people, not a posture fault; the actual imbalance worth avoiding is upper trap work with no middle or lower trap work alongside it.

One useful check: if overhead pressing feels like it runs out of room before the arms are vertical, the limit is often the shoulder blade failing to rotate far enough rather than the shoulder joint itself, and that rotation belongs to the trapezius and the serratus anterior together.

Anatomy

Origin
  • External occipital protuberance and the medial third of the superior nuchal line
  • Nuchal ligament
  • Spinous processes of the seventh cervical to twelfth thoracic vertebrae
Insertion
  • Posterior border of the lateral third of the clavicle
  • Acromion
  • Upper crest of the spine of the scapula
Actions
  • Elevates the shoulder girdle, through the upper fibres
  • Retracts the scapula toward the spine, through the middle fibres
  • Depresses the scapula, through the lower fibres
  • Rotates the scapula upward so the arm can reach overhead, with all three parts working together
Innervation
Accessory nerve (CN XI), with proprioceptive fibres from the cervical plexus (C3–C4)

Parts of this muscle

Exercises

Antagonists

Synergists