Rhomboid major

What it is

A flat, roughly rhomboid sheet running downward and outward from the upper thoracic spine to the inner edge of the shoulder blade. It lies beneath trapezius, so it cannot be seen, though the gap between the shoulder blades where it works can certainly be felt.

Rhomboid minor sits directly above it and is often continuous with it — the division between the two is not always clear in dissection, and some people effectively have one muscle.

What it does

Retracts the scapula — draws it towards the spine. Because its fibres run diagonally downward from spine to blade, it also elevates the blade slightly and rotates it so the socket turns downward.

That downward-rotating action makes it a direct opponent of serratus anterior and of the upper and lower trapezius working as a couple. It is also why it is loaded in pulling the arm down from overhead.

It holds the scapula against the pull of anything drawing the arm forward.

What loads it

Rowing and any horizontal pulling, where the shoulder blades are drawn back against resistance. Pulling down from overhead loads it too, via its downward-rotating action.

The inverted row is the direct one, and the pull-up loads it through its downward-rotating action.

What is commonly got wrong about it

"Squeeze your shoulder blades together" as universally good form. Retraction is a normal movement and this muscle produces it. The instruction is often given as though the position itself were corrective, and a fixed retracted scapula is not more correct than a mobile one — the shoulder blade is supposed to move.

That interscapular pain is a rhomboid problem. Pain between the shoulder blades is very common and frequently referred from the neck or thoracic spine rather than arising in the muscle you can feel it in. Referred pain is genuinely felt where it is felt.

That rhomboids and mid-trapezius can be separated. They overlap in action and are loaded together in every rowing movement.