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 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.

The top part of your chest muscle is really good at helping your arm move forward, while the middle part keeps your shoulder steady and the bottom part helps pull your arm backward — based on how these parts are shaped in dead bodies studied by scientists.

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 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.

In dead bodies, the front and middle parts of the shoulder muscle are best at lifting the arm out to the side, while certain chest and back muscles are better at pulling the arm back down because of how they're positioned.