biceps

The biceps brachii, commonly called the biceps, is a two-headed muscle of the upper arm located in the anterior compartment between the shoulder and elbow. It has two proximal origins: the short head from the coracoid process of the scapula and the long head from the supraglenoid tubercle. The two heads join into a single muscle that inserts via a tendon on the radial tuberosity and, through the bicipital aponeurosis, into the antebrachial fascia.

The primary actions of the biceps are elbow flexion and forearm supination, especially when the forearm is in a supinated position. The muscle also assists with shoulder flexion and contributes to joint stability of the glenohumeral joint through its proximal tendon.

Innervation is provided by the musculocutaneous nerve (C5-C7). Blood supply comes from branches of the brachial artery, with muscular branches supplying the proximal portion and forearm vessels contributing to distal supply.

Clinical significance includes distal biceps tendon injuries, which can cause a Popeye deformity (bulging of the muscle belly) and weakness in flexion and supination. Tendinopathy and partial tears may occur with overuse or heavy lifting. Diagnosis is typically clinical and can be aided by ultrasound or MRI.

Variants are usually limited to differences in the two heads, though occasional accessory or anomalous heads are described in anatomical literature. The biceps brachii is a key muscle for upper limb flexion and forearm rotation, and its function is frequently evaluated in orthopedic and sports contexts.