The biceps brachii is a two‑headed muscle of the anterior arm, crossing both shoulder and elbow joints.
Anatomy
- Long head: Originates from supraglenoid tubercle of scapula; tendon traverses glenohumeral joint within bicipital groove.
- Short head: Originates from coracoid process of scapula.
- Insertion: Common tendon → radial tuberosity + bicipital aponeurosis (lacertus fibrosus) into deep forearm fascia.
Actions
- Primary: Elbow flexion (maximal at 90° flexion, supinated forearm).
- Primary: Forearm supination (most powerful supinator).
- Accessory: Weak shoulder flexion, abduction (long head); stabilization of humeral head.
Biomechanical Nuance
- Moment arm for flexion peaks at 90°; for supination, peaks at neutral.
- Brachialis is the pure flexor (inserts on ulna, not radius); brachioradialis assists in mid‑prone.
Common Pathologies
- Distal tendon rupture: "Popeye" deformity; usually middle‑aged men, eccentric load. Surgical repair for active patients.
- Proximal (long head) tendinopathy/rupture: Often in rotator cuff disease; may be managed non‑operatively.
- Bicipital tunnel syndrome: Median nerve compression at lacertus fibrosus.
Examination
- Speed's test, Yergason's test (long head tendinopathy).
- Hook test (distal rupture).
- Resisted supination + flexion at 90° isolates biceps.
The biceps is a versatile muscle critical for both power and fine motor control of the forearm.
