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The humerus is a complex ball-and-socket joint that includes the head of the humerus, the clavicle (collarbone), and the scapula. The shoulder's primary motions include flexion, extension, abduction, adduction, internal rotation, and external rotation. Adduction is the action of lowering the arm toward the body, and several muscles are involved in the adduction of the humerus.
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What You'll Learn
The pectoralis major muscle
The pectoralis major is the only muscle responsible for keeping the arm attached to the trunk of the body. It is innervated by the medial (C8-T1) and lateral (C5-C7) pectoral nerves, which originate from the medial and lateral cords, respectively. The medial pectoral nerve innervates the lateral sternocostal head, while the lateral pectoral nerve innervates the clavicular head and medial sternocostal head. The pectoralis major receives its blood supply via the pectoral branch of the thoracoacromial artery.
The primary functions of the pectoralis major are flexion, adduction, and internal rotation of the humerus. It is also capable of humeral flexion when the arm is in a position of extension posterior to the coronal plane of the thorax. Exercises that include humeral adduction, elbow extension, and a pressing motion induce activation of the sternocostal muscle fibres. The pectoralis major can be targeted from numerous training angles along the sternum and clavicle. Exercises that include horizontal adduction and elbow extensions such as the barbell bench press, dumbbell bench press, and machine bench press induce high activation of the pectoralis major in the sternocostal region.
Injuries of the pectoralis major are uncommon but have become more prevalent over the past 20 years due to increased participation in weight lifting. Tears of the pectoralis major are rare and typically affect otherwise healthy individuals. However, they may result in pain, weakness, and muscular deformity. Poland syndrome is a rare congenital condition in which the pectoralis major muscle is missing, usually on one side of the body.
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The latissimus dorsi muscle
The latissimus dorsi works collaboratively with the teres major and pectoralis major muscles to perform actions of the upper extremity. Together, these muscles adduct, medially rotate, and extend the arm at the glenohumeral joint. The latissimus dorsi also assists in depression of the arm with the teres major and pectoralis major. It is also active in moving the trunk forward and upward when the upper extremities are fixed overhead.
The latissimus dorsi is supplied predominantly by the thoracodorsal artery, a continuation of the subscapular artery, which is a branch of the third part of the axillary artery. It also receives blood supply from the dorsal perforating branches of the inferior three posterior intercostal arteries and the superior three lumbar arteries. The thoracodorsal nerve, a branch of the posterior cord of the brachial plexus, provides innervation to the latissimus dorsi.
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The teres major muscle
The main function of the teres major is to produce movements of the humerus at the glenohumeral joint. By contracting, it pulls the humerus posteriorly (extension) and rotates it medially towards the trunk (internal rotation). Additionally, it contributes to the stabilization of the shoulder joint. The teres major is also a medial rotator and adductor of the humerus and assists the latissimus dorsi in drawing the previously raised humerus downwards and backwards (extension, but not hyperextension).
Isolated teres major injuries are rare but are almost exclusively encountered in professional and high-level recreational athletes, especially baseball pitchers. The main symptom of a teres major tear is a sudden sharp pain in the shoulder, upper arm, and armpit. This usually arises if the muscle is not given rest and no treatment is carried out. The pain is usually dull and intensifies with physical activity and hand-behind-back activities, such as pitching in baseball or serving a tennis ball. Teres Major Strain often occurs when a proper warm-up is not done before workouts.
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The triceps
The radial nerve originates from the posterior cord of the brachial plexus in the anterior axilla. The nerve then courses along with the profunda brachii artery and travels through the arm inferolaterally. It passes behind the humerus and through the radial groove between both the lateral and medial heads of the triceps brachii. All three heads of the triceps brachii are classically believed to be innervated by the radial nerve. However, more recent studies observed that in around 14% of individuals, the long head of the triceps brachii was innervated by the axillary nerve, and in 3% it received dual innervation from both the radial nerve and axillary nerve.
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The coracobrachialis
The main function of the coracobrachialis is to produce flexion and adduction of the arm at the shoulder joint. It helps to bend the upper arm and bring it close to the body. It also plays a role in stabilising the shoulder joint. The coracobrachialis is innervated by the musculocutaneous nerve, which arises from the anterior division of the upper trunk (C5-C7). The muscle receives its blood supply from the muscular branches of the brachial artery, with additional supply from the anterior circumflex humeral and thoracoacromial arteries.
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Frequently asked questions
There are several muscles that adduct the humerus, including the pectoralis major, latissimus dorsi, teres major, triceps, and coracobrachialis.
The pectoralis major is a large muscle located in the chest that is responsible for flexion, internal rotation, and adduction of the shoulder.
The latissimus dorsi is a large, flat muscle in the back that covers the lower and lateral sides of the back and the lateral part of the chest. It is responsible for internal rotation, extension, and adduction of the shoulder.
Coracobrachialis is a muscle that originates from the coracoid process and inserts at the medial aspect of the middle of the humerus. It is responsible for flexion and adduction of the arm.
