Shoulder flexion is the movement of raising the arm forward, achieved through the glenohumeral joint and aided by muscles such as the pectoralis major, anterior deltoid, biceps, and others depending on arm rotation.
Shoulder flexion is the action of raising the arm forward in front of the body. Initiated by the pectoralis major and anterior deltoid muscles with the help of the biceps, flexion occurs at the glenohumeral or shoulder joint, which is a ball and socket joint. From a starting position with the arm down to the side, approximately 180 degrees of flexion can be achieved until the arm is directly overhead. Flexion can occur palm in, palm back, or palm forward.
The glenohumeral joint is a joint between the head or ball of the humerus bone in the upper arm and the socket formed by the glenoid socket of the scapula. A type of synovial or movable joint called a ball and socket joint, the shoulder allows movement of the arm in almost all directions as the head of the humerus rotates in the glenoid socket like a ball in a cup. One of these movements is the shoulder flexion, in which the arm is raised vertically in a forward direction.
Shoulder flexion is made possible primarily by two major upper body muscles: the pectoralis major and the anterior deltoid. In the pectoralis major muscle of the thorax, an upper section known as the clavicular head that arises from the clavicle and attaches to the front of the humerus is responsible for flexing the arm forward. Adjacent to the clavicular head of the pectoralis major is the anterior section of the deltoid, the muscle that covers the shoulder. Originating from the clavicle just lateral to the pectoralis and inserting on the front lateral aspect of the humerus, the anterior deltoid works with the clavicular head of the pectoralis to produce shoulder flexion. It is particularly active when the elbow is angled outward.
Other muscles are involved in shoulder flexion depending on the rotation of the shoulder during flexion. When the arm is rotated so that the palm of the hand faces forward, the biceps brachii and coracobrachialis muscles on the upper forearm help lift the arm forward. Its contribution is weaker when the arm is neutral. However, in a medially or internally rotated position, the pectoralis minor in the thorax, as well as the subscapularis muscle of the rotator cuff, assist in shoulder flexion, especially by stabilizing the head of the humerus in the glenoid socket when the arm is raised. .
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