The infraspinatus muscle is attached along the broad inner edge of the scapula (shoulder blade). It narrows into a strong tendonthat joins firmly to the top of the humerus (upper arm bone). The infraspinatus muscle sits on the back of the shoulder blade below the spine and under the deltoid muscle. It works with the supraspinatus to help lift and twist the upper arm. These two muscles also help support and protect the shoulder joint by keeping the head of the humerus in place.

The base of this triangular muscle is attached along the lumbar and lower half of the thoracic vertebrae (spine), the lower ribs, and even the hip bones far below. The latissimus dorsi is a wide, flat muscle located on the lower half of the back. The muscle fibers at its tip insert under the scapula (shoulder blade) and join to the humerus (upper arm bone) in the shoulder. This muscle gives your arms motion. It is used when swimming or when you swing your arms back when jogging. It is also used to reach up to grab something above your head.