When studying dead shoulders, most big shoulder muscles change what they do depending on how the arm is positioned — but one part, the bottom part of a muscle called subscapularis, always does the same job: helping the arm move inward and across the body, no matter the position.

The shoulder muscle called supraspinatus switches jobs depending on how you move your arm — it pulls one way when you lift your arm forward and the opposite way when you lift it backward, like a muscle with two different gears.

In dead shoulders, two muscles help lift the arm but twist it in opposite ways—one turns it outward, the other inward—so they work together like a team that also pushes against each other to keep the shoulder steady.

Your shoulder muscles don’t work the same way every time — different parts of them take the lead or help out depending on which way you’re pushing or pulling, kind of like team members switching roles during different tasks.