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I'm actually an artist, but I wanted to ask this because it will help a lot in my figure drawings.

My artistic anatomy teacher taught me about the Scapulohumeral Rhythm. He said that in during the first 30 degree of rotation of the humerus, neither the scapula nor the clavicle moves. But after that, for the next 60 degree of rotation of the humerus, its rotation is distributed in a 2:1 ratio to the Scapulathoracic joint. He said that beyond that, the Humerus is locked into the socket with Acromium and Coracoid Process. So the Glenohumeral Joint is frozen. Additional elevation comes from the Clavicle.

My first question is how true is that? My second question is what happens to the Scapula after the 90 degrees rotation of the Humerus? I noticed that the Scapula keeps rotating even after the Humerus is rotated beyond 90 degrees, but is there any consistent ratio? My third question is what is the maximum elevation of the Humerus in degrees?

Forgive me if I looked liked an annoying dumbass, I'm just an artist. So, please explain in a simple and understandable way.

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