Final answer:
The deltoid muscle is essential for shoulder abduction but also supports other arm movements due to the shoulder joint's complex structure. It is prone to injuries due to repetitive movements. The scapula's superior and inferior rotations facilitate full range shoulder movements.
Step-by-step explanation:
The deltoid is a key shoulder muscle responsible for abducting the arm, which is moving it away from the body's midline. This muscle is multipennate, meaning its fibers are arranged at multiple angles, allowing for a range of movements. When the middle fibers of the deltoid contract, they specifically perform abduction, which is critical in movements such as reaching out to the side. The deltoid also participates in other actions like flexion, which brings the arm forward, medial rotation, extension (moving the arm backward), and lateral rotation, which rotates the arm away from the body. The anatomical design of the shoulder joint and the coordination of muscles like the deltoid, subscapularis, supraspinatus, infraspinatus, teres major, teres minor, and coracobrachialis, provides a wide range of arm movements.
Due to the complexity and frequent use of the shoulder in activities requiring abduction, such as swimming or throwing, it is prone to injuries. These can include inflammation of the tendons or bursa, tears of the glenoid labrum, or rotator cuff injuries. Superior and inferior rotations of the scapula also play a crucial role in full abduction and adduction of the arm, respectively.