The coracobrachialis is a spindle-shaped muscle located deep within the upper arm, often overshadowed by larger muscles like the biceps and deltoid. Despite its small size, it is an important component of the shoulder and arm complex. It plays a role in the movement and stability of the glenohumeral (shoulder) joint. Understanding this muscle provides a more complete picture of how the arm moves.
Locating the Coracobrachialis
The coracobrachialis is situated in the anterior compartment of the upper arm, running beneath the biceps brachii muscle. Its name is derived directly from its two attachment points. The muscle originates from the coracoid process, a small, hook-like bony projection extending from the scapula (shoulder blade).
From this origin, the muscle extends downward and inserts onto the medial side of the humerus approximately halfway down its shaft. This deep positioning means it shares an origin with the short head of the biceps and is closely associated with the neurovascular bundle of the axilla (armpit). The entire muscle is innervated by the musculocutaneous nerve, comprised of nerve fibers from the C5, C6, and C7 spinal nerve roots.
Primary Actions and Role in Movement
The coracobrachialis acts on the shoulder joint, contributing to two primary movements of the arm. Its most recognized function is assisting in shoulder flexion, which involves lifting the arm forward (e.g., reaching out or raising the arm to shoulder height). This action is performed in conjunction with larger flexor muscles, where the coracobrachialis provides supplementary force.
The muscle also assists in shoulder adduction, the movement of bringing the arm inward toward the midline of the body. Beyond these movements, the coracobrachialis functions as a stabilizer of the shoulder joint. By maintaining tension, it helps keep the head of the humerus firmly seated within the shoulder socket during dynamic movements, preventing excessive displacement.
This stabilizing role is important when the arm is moved away from the body, helping to resist downward deviation. Movements such as throwing a ball, pushing open a heavy door, or carrying a weight close to the body all engage the coracobrachialis. Although considered a weak muscle compared to its neighbors, its consistent involvement highlights its functional importance.
Symptoms of Strain and Overuse
When subjected to overuse or strain, the coracobrachialis can develop myofascial trigger points (localized knots of muscle tissue). These points cause localized pain in the front of the shoulder and are known for their referred pain patterns. The discomfort often radiates down the back of the upper arm and forearm, sometimes reaching the back of the hand, which can be mistaken for nerve-related pain.
Activities involving repeated, forceful use, such as weightlifting or gymnastics, may lead to tightness and strain. This tightness can restrict the shoulder’s range of motion, making it painful or difficult to fully flex the arm forward or reach across the body. An injured coracobrachialis can also cause a deep, aching sensation that may be misdiagnosed as an issue with the deeper rotator cuff muscles or the biceps tendon.