When you pull yourself under the bar, a muscle called your serratus anterior kicks on to help create a stable platform. This is a muscle that sits on the back side of your ribs and connects to your shoulder blades. The Serratus muscle when activated correctly pulls the shoulder blade forward and out to the side away from the middle of the spine. This is the motion of protraction. It can also help with upward rotation which this video doesn’t show, meaning the lower part of the shoulder blade rot

The serratus anterior muscle #muscles #anatomy | Dr. Ishtiaque Arafat