The biceps brachii is the prominent two-headed muscle of the anterior upper arm, instantly recognisable as the 'flexed arm' muscle, though its most mechanically significant function is actually forearm supination rather than simple elbow flexion. Its long head has an unusually complex path, beginning at the top of the shoulder socket and travelling through the joint before descending the arm, making it vulnerable to shoulder pathology. The two heads merge into a single belly and end in a distal tendon attaching to the radius and a broad aponeurosis spanning the forearm.
| Origin | Supraglenoid tubercle of the scapula, travels through the glenohumeral joint in the bicipital groove; Apex of the coracoid process of the scapula |
|---|---|
| Insertion | Radial tuberosity of the radius; Bicipital aponeurosis blending into the forearm fascia |
| Nerve Supply | Musculocutaneous nerve (C5, C6) |
| Blood Supply | Brachial artery |
| Actions | Flexion of the elbow (most powerful when forearm is supinated); Supination of the forearm (most powerful when elbow is at 90°); Weak flexion of the shoulder |
|---|
The biceps is uniquely capable of combining elbow flexion with forearm supination in a single coordinated movement, making it mechanically dominant in any activity that requires both actions simultaneously, such as turning a screwdriver or lifting a bowl with the palm up.
Long head biceps tendinopathy is a common anterior shoulder pain complaint, particularly in overhead athletes and middle-aged active adults, producing a dull ache that worsens with resisted elbow flexion and overhead reaching and is reproduced by Speed's and Yergason's tests. Distal biceps tendon ruptures are far less common but tend to occur in men during sudden eccentric loads on the elbow, the characteristic 'Popeye deformity' where the muscle belly bunches proximally is diagnostic. Complete distal ruptures require surgical reattachment in active individuals to restore supination strength.
The biceps belly is easily palpable along the anterior upper arm with the elbow flexed against resistance and the forearm supinated. The distal tendon can be felt as a firm cord just above the elbow crease, and the long head tendon is palpable with firm pressure in the bicipital groove of the humerus.
Degenerative irritation of the long head tendon within the bicipital groove, producing anterior shoulder pain that is aggravated by overhead activities, resisted elbow flexion, and forearm supination, and often co-exists with rotator cuff pathology.
Avulsion of the biceps tendon from the radial tuberosity during an eccentric load on a flexed elbow, causing a visible proximal retraction of the muscle ('Popeye sign'), bruising in the antecubital fossa, and significant weakness in supination that exceeds the loss of elbow flexion strength.
Partial tearing of the biceps muscle fibres during heavy curling or pulling, most commonly at the musculotendinous junction, presenting with localised anterior arm pain, swelling, and weakness proportional to the extent of the tear.
