Supraspinatus anatomy presents as a simple strip of mucle. It attaches to the top of the scapula and inserts on the head of the humerus. More extensive studies have been done because of its association with shoulder impingement and tendinopathy. In fact, it is more complex than it appears.
Actually, more recent studies, like this one, consistently show that it has two distinct sections. The anterior section has bipennate fibers with a thick tubular tendon. The posterior section has parallel fibers and a thin strap-like tendon. Each section has superficial, medial, and deep subsections.
These sections and subsections appear to engage independently. Supraspinatus seems very active during abduction of the humerus of about 150 degrees. Also, electromyographical studies show that it is active during flexion of the humerus to about 150 degrees.
As a rotator cuff muscle, it secures the head of the humerus in the glenoid fossa. It does this with an overhead strap, which is, unfortunately, susceptible to tears. This support is assisted by the deltoid, which acts like a sling that prevents the entire humerus from sliding inferiorly in the glenoid fossa.
Origin – medial two-thirds of the supraspinous fossa
Insertion – Superior facet of the greater tubercle of the humeral head
Function – abduction of the humerus