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.

When young guys quickly push or pull with their shoulders, different parts of key shoulder muscles turn on together in a smart way—and how they work together changes depending on the direction of the move.

Different parts of big shoulder muscles actually work in their own unique ways because they pull with different strength and direction — kind of like how different sections of a fan blade might push air differently.

When you lift your arm out in front of you, certain shoulder muscles are better at helping the movement because of how they're positioned, while others are stronger at pulling the arm back down.

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.