How do I examine the brachioradialis (C5‑C6) reflex?

How to Examine the Brachioradialis Reflex

To examine the brachioradialis (C5-C6) reflex, position the patient's forearm in a neutral (midway) position between supination and pronation with the elbow flexed to approximately 90 degrees, then strike the distal radius (radial styloid) with a reflex hammer, observing for flexion of the elbow and slight supination of the forearm.

Patient Positioning

• Seat the patient comfortably with the arm relaxed and supported 1
• Position the forearm in the neutral (90-degree) position between full supination and full pronation, as this is critical for eliciting the reflex 1
• Flex the elbow to approximately 90 degrees to optimize muscle length and reflex response 2
• The patient's hand can rest on their thigh or be supported by the examiner 1

Technique for Eliciting the Reflex

• Strike the distal radius (at the radial styloid process, approximately 2-3 cm proximal to the wrist) with a reflex hammer using a brisk, controlled tap 1
• The hammer should contact the bone directly, not the tendon 1
• Observe for elbow flexion as the primary response, with possible slight supination of the forearm 3, 4
• The brachioradialis muscle belly (visible on the lateral forearm) should contract visibly 5

Expected Normal Response

• Normal response consists of visible contraction of the brachioradialis muscle with resultant elbow flexion 1, 3
• The reflex can be elicited by both stretch and phasic vibration transmitted through the bone 1
• The response is typically graded on a 0-4+ scale using standard reflex grading criteria 2

Critical Technical Considerations

• Forearm position is crucial: The reflex response dramatically decreases or disappears when the forearm is fully supinated, as the brachioradialis becomes mechanically disadvantaged in this position 1
• In 94% of normal individuals, tapping the radius with the forearm in full supination causes the biceps contraction to disappear, with EMG amplitude decreasing from 1.1 to 0.2 mV 1
• The brachioradialis functions primarily as an elbow flexor regardless of forearm position, with greatest activity during flexion tasks 3, 4
• The muscle demonstrates peak electromyographic activity at the end of elbow flexion in 73.3% of individuals 3

Common Pitfalls to Avoid

• Do not test with the forearm in full supination, as this position significantly diminishes or abolishes the reflex response in normal individuals 1
• Do not confuse with the biceps reflex, which is tested by striking the biceps tendon in the antecubital fossa 1
• Avoid striking too proximally or distally on the radius, as the optimal site is the distal radial shaft near the styloid process 1
• Be aware that in patients with hyperreflexia (such as stroke patients), the reflex may persist even in supination in 84% of cases, which is abnormal 1

Clinical Significance

• The brachioradialis reflex tests the C5-C6 nerve roots and is useful in localizing cervical radiculopathy 6, 7
• Asymmetry between sides or absent reflexes may indicate nerve root pathology 2
• Hyperactive reflexes may indicate upper motor neuron lesions, while diminished or absent reflexes suggest lower motor neuron or nerve root pathology 2, 1
• The brachioradialis muscle is commonly involved in overuse syndromes and can be a source of forearm pain that may confound the examination 5