Biceps Brachii: Origin, Insertion, Action, Nerve & Clinical Testing

The Biceps Brachii is arguably the most famous muscle in the human body. As the Latin name suggests (Bi = two, Cephal = head), it is a two-headed muscle spanning the anterior arm. While primarily known for flexing the elbow, it is actually the most powerful supinator of the forearm.

Quick Anatomy Snapshot

Origin (Proximal)	Short Head: Tip of the Coracoid Process of the Scapula. Long Head: Supraglenoid Tubercle of the Scapula (passing through the bicipital groove).
Insertion (Distal)	Radial Tuberosity and the Bicipital Aponeurosis (Deep fascia of medial forearm).
Nerve Supply	Musculocutaneous Nerve (C5, C6).
Blood Supply	Brachial Artery.
Primary Actions	Supination: Turning the palm up (strongest when elbow is flexed 90°). Elbow Flexion: Bending the elbow. Shoulder Flexion: Weak assistance in lifting the arm forward.

Deep Dive: The "Corkscrew" Muscle

While everyone associates the biceps with curling a dumbbell, its mechanics are more complex.

1. The Supination Mechanism

Because the muscle inserts onto the Radial Tuberosity (which is on the medial side of the radius when pronated), pulling on this insertion unwinds the radius, spinning the palm upward. This is why you need your biceps to drive a screw in with a screwdriver or turn a tight doorknob.

2. Two Heads, Two Joints

Both heads cross the shoulder joint and the elbow joint.
• The Long Head helps depress the humeral head, stabilizing the shoulder joint.
• The Short Head works with Coracobrachialis to stabilize the scapula.

Physio Corner: Clinical Relevance

💪 Functional Fact: The Biceps is mechanically disadvantaged when the forearm is pronated (palm down). In this position, the Brachialis muscle takes over as the primary flexor. To maximally recruit the biceps, you must flex with the palm up (supinated).

Palpation

The muscle belly is easily palpable on the anterior arm. The tendon of the long head can be felt in the intertubercular groove of the humerus. The distal tendon is a thick cord in the cubital fossa (front of the elbow).

⚠️ Clinical Pathology: Distal Biceps Rupture
This usually occurs when lifting a heavy object with the elbows bent (eccentric load). The tendon tears off the radius, causing the muscle to retract up the arm ("Reverse Popeye Sign").
The Hook Test: The therapist tries to "hook" their finger under the distal tendon from the lateral side. If the tendon is absent, the test is positive.

Manual Muscle Testing (MMT)

To test the Biceps Brachii, we must combine flexion with supination.

Testing Tip: If you allow the patient to pronate, they will use their Brachioradialis and Brachialis. Keep the palm facing the shoulder!

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Sitting. Arm at side, forearm Supinated (Palm up). Action: Patient flexes the elbow, bringing the hand to the shoulder. Resistance: Applied at the distal forearm (wrist), pulling down into extension. Grade 3: Full range against gravity. Grade 4/5: Holds against moderate/max resistance.
Grade 2 (Gravity Eliminated)	Position: Sitting with arm supported on a table at shoulder height (90° abduction), forearm supinated. Action: Patient slides the hand toward the shoulder (flexion). Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate the anterior arm or the tendon in the cubital fossa. Cue: "Try to bend your elbow." Grade 1: Trace contraction felt. Grade 0: No activity.

Frequently Asked Questions

Why does the long head rupture more often?

The Long Head tendon takes a sharp 90-degree turn over the humeral head and creates friction within the bicipital groove. This "wear and tear" makes it prone to fraying and proximal rupture ("Popeye Deformity").

Does the Biceps Brachii attach to the Ulna?

No. It attaches to the Radius. The Brachialis attaches to the Ulna. This is why the Biceps can rotate the forearm (supinate), but the Brachialis cannot.

What is the Bicipital Aponeurosis?

It is a flat sheet of fascia that fans out from the distal biceps tendon medially. It protects the underlying brachial artery and median nerve in the cubital fossa.

Test Your Knowledge: Biceps Brachii Quiz

1. Which nerve supplies the Biceps Brachii?

2. Where does the Short Head originate?

3. What is the primary insertion of the Biceps?

4. To maximally activate the Biceps during flexion, the forearm should be:

5. The "Popeye Deformity" typically indicates rupture of which tendon?

6. The Bicipital Aponeurosis provides protection for the:

7. Which muscle is the primary antagonist to the Biceps Brachii?

8. The Long Head tendon passes through which groove?

9. Which action is the Biceps Brachii strongest at?

10. True or False: The Biceps Brachii is the only flexor of the elbow.

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Magee, D. J. (2014). Orthopedic Physical Assessment. 6th ed. Elsevier.