The Structure of the Shoulders
The shoulders consist of several muscles that work together to enable a wide range of movements. Among these muscles are the deltoids, which are the most superficial muscles, and the rotator cuff, which is composed of deeper muscles.
The deltoid muscle
The deltoid muscle is composed of three bundles: the anterior bundle, the lateral bundle, and the posterior bundle.
The anterior bundle
The anterior bundle inserts on the anterior part of the acromion (the end of the shoulder blade) and descends to attach to the anterior surface of the humerus, near the humeral shaft. It is involved in shoulder forward flexion and adduction.
The lateral bundle
The lateral bundle inserts on the lateral part of the acromion and descends to attach to the lateral surface of the humerus, near the humeral shaft. It is used in shoulder abduction.
The posterior bundle
The posterior bundle inserts on the posterior part of the spine of the scapula and descends to attach to the posterior surface of the humerus, near the humeral shaft. It is responsible for shoulder backward extension.
The rotator cuff
The rotator cuff is a group of four muscles located at the back and around the shoulder, with tendons attaching to the head of the humerus.
They are responsible for stabilizing the shoulder and assist the deltoids in movements. The rotator cuff muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis.
The supraspinatus
The supraspinatus is located above the shoulder blade. It inserts on the supraspinous fossa of the scapula and joins the greater tubercle of the humerus (upper surface). It plays a crucial role in arm elevation and shoulder abduction.
The infraspinatus
The infraspinatus and teres minor are situated at the back of the shoulder. The infraspinatus inserts on the infraspinous fossa of the scapula and joins the greater tubercle of the humerus (posterior and medial surface). The teres minor inserts on the lateral border of the scapula and joins the greater tubercle of the humerus, similar to the infraspinatus. They are involved in external rotation of the shoulder.
The subscapularis
The subscapularis is located at the front of the shoulder blade. It inserts on the subscapular fossa of the scapula and joins the anterior surface of the humerus between the greater and lesser tubercles. It is responsible for internal rotation of the shoulder.
Video illustration
Main exercises
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