Biceps Brachii

1. Overview

The biceps brachii is a prominent, two-headed muscle located in the anterior compartment of the upper arm. It is primarily responsible for forearm flexion and supination, playing a key role in elbow and shoulder movements. The term “biceps” means “two heads,” referring to its dual origin from the scapula. Due to its visibility and size, the biceps is commonly associated with strength and is a key muscle in both athletic performance and clinical rehabilitation.

2. Location

The biceps brachii is situated in the anterior upper arm, between the shoulder and the elbow:

• Proximal attachment:

  • Long head: Supraglenoid tubercle of the scapula (via the intertubercular groove).

  • Short head: Coracoid process of the scapula.

• Distal attachment: Radial tuberosity of the radius and bicipital aponeurosis into the deep fascia of the forearm.

It lies superficial to the brachialis muscle and is covered by skin and fascia in the upper arm.

3. Structure

The biceps brachii has two heads and a shared distal tendon:

• Long head: Travels through the shoulder joint and the intertubercular groove of the humerus; more lateral.

• Short head: Lies medially and shares a common origin with the coracobrachialis.

• Muscle belly: The two heads converge into a single, thick, fusiform muscle belly.

• Distal tendon: Inserts on the radial tuberosity and gives off a flat sheet—the bicipital aponeurosis—to blend with forearm fascia.

The biceps is innervated by the musculocutaneous nerve (C5–C7) and receives its blood supply from the brachial artery.

4. Function

The biceps brachii has both primary and secondary functions involving the forearm and shoulder:

• Forearm supination: Most powerful supinator of the forearm when the elbow is flexed.

• Elbow flexion: Assists in flexing the forearm, especially during supinated movements (e.g., lifting a dumbbell).

• Shoulder flexion: Both heads help in raising the arm at the shoulder joint.

• Shoulder stabilization: Long head helps stabilize the humeral head within the glenoid cavity during arm motion.

5. Physiological role(s)

Beyond movement, the biceps brachii contributes to several physiological roles:

• Functional strength: Used extensively in lifting, pulling, and carrying tasks.

• Muscle tone and contour: Plays a cosmetic role in upper arm appearance; often targeted in strength training.

• Reflex testing: The biceps reflex (C5) is a clinical tool for evaluating the integrity of the musculocutaneous nerve and spinal segment function.

• Joint protection: Helps protect the elbow joint by dynamically supporting forearm movement under load.

6. Clinical Significance

The biceps brachii is involved in various injuries and clinical conditions:

• Biceps tendinitis:

  • Inflammation of the long head tendon, often from overuse or repetitive overhead activity (e.g., in swimmers or throwers).

• Biceps tendon rupture:

  • Typically involves the long head; may cause a visible bulge (“Popeye deformity”) and weakness in supination and flexion.

• Bicipital groove instability:

  • The long head tendon can sublux or dislocate from the intertubercular groove, causing clicking and pain.

• Musculocutaneous nerve injury:

  • May result in weakened flexion/supination and sensory deficits in the lateral forearm.

• Biceps reflex testing:

  • Used in neurological exams to assess C5 spinal cord function. Absence may indicate upper motor neuron lesions or peripheral nerve damage.

• Overuse syndromes:

  • Common in athletes and manual laborers; can lead to chronic strain and functional limitation if not addressed early.