Rotator Cuff Muscles

A 52-year-old right-handed carpenter presents with 3 months of progressive right shoulder pain and weakness. He reports difficulty initiating arm abduction and lifting objects overhead. On examination, the **Empty Can (Jobe) test** is positive, with pain and weakness when the arm is held abducted 90°, forward-flexed 30° in the scapular plane with thumbs pointing downward, and downward pressure is applied. MRI confirms a full-thickness tear of the structure marked **A** in the diagram. Which of the following best explains why the structure marked **A** is the most commonly torn rotator cuff tendon?