Muscles around the Shoulder
Major Muscles
The muscles that are responsible for movement in the shoulder attach to the Scapula, Humerus, and Clavicle. The muscles that surround the shoulder form the Shoulder Cap and underarm.
| Scapular Retraction(aka Scapular Adduction) | The Scapula is moved posteriorly and medially along the back, moving the arm and Shoulder Joint posteriorly. | Rhomboideus major, minor, and trapezius. |
| Scapular Protraction(aka Scapular Abduction) | The opposite motion of Scapular Retraction. The Scapula is moved anteriorly and laterally along the back, moving the arm and Shoulder Joint anteriorly. | Serratus anterior (prime mover), pectoralis minor and major. |
| Scapular Elevation | The Scapula is raised in a shrugging motion. | Levator scapulae, the upper fibers of the trapezius. |
| Scapular Depression | The Scapula is lowered from elevation. The Scapula may be depressed so that the angle formed by the neck and Shoulders is obtuse, giving the appearance of "slumped" Shoulders. | Pectoralis minor, lower fibers of the trapezius, subclavius, latissimus dorsi. |
| Arm Abduction | Arm Abduction occurs when the arms are held at the sides, parallel to the length of the torso, and are then raised in the plane of the torso. This movement may be broken down into two parts: True Abduction of the arm, which takes the humerus from parallel to the spine to perpendicular; and Upward Rotation of the Scapula, which raises the humerus above the Shoulders until it points straight upwards. | True Abduction: supraspinatus (first 15 degrees), deltoid; Upward rotation : trapezius, serratus anterior. |
| Arm Adduction | Arm Adduction is the opposite motion of Arm Abduction. It can be broken down into two parts: Downward rotation of the Scapula and True adduction of the arm. | Downward rotation : pectoralis minor, pectoralis major, subclavius, latissimus dorsi (same as scapular depression, with pec major replacing lower fibers of trapezius); True Adduction: same as downward rotation with addition of teres major and the lowest fibers of the deltoid. |
| Arm Flexion | The Scapula is moved posteriorly and medially along the back, moving the arm and Shoulder Joint posteriorly. | Pectoralis major, coracobrachialis, biceps brachii, anterior fibers of deltoid. |
| Arm Extension | The Humerus is rotated out of the plane of the torso so that it points backwards (posteriorly). | Latissimus dorsi and teres major, long head of triceps, posterior fibers of the deltoid. |
| Medial Rotation of the Arm | Medial Rotation of the Arm is most easily observed when the elbow is held at a 90-degree angle and the fingers are extended so they are parallel to the ground. Medial Rotation occurs when the arm is rotated at the shoulder so that the fingers change from pointing straight forward to pointing across the body. | Subscapularis, latissimus dorsi, teres major, pectoralis major, anterior fibers of deltoid. |
| Lateral Rotation of the Arm (aka Scapular Adduction) | Movement of the Shoulder in a circular motion so that if the elbow and fingers are fully extended, the subject draws a circle in the air lateral to the body. In circumduction, the arm is not lifted above parallel to the ground so that "circle" that is drawn is flattened on top. | Pectoralis major, subscapularis, coracobrachialis, biceps brachii, supraspinatus, deltoid, latissimus dorsi, teres major and minor, infraspinatus, long head of triceps. |