Clinical Neurology · Neuro-Muscular

NCS — Technique and Normal Values

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Reference values and recording & stimulation technique for routine nerve conduction studies. For each region the data is split into two cross-referencing tables: Normal values (latency, amplitude, conduction velocity, F-wave) and Recording & stimulation technique (electrode placement and stimulation sites). Both tables list the same nerves in the same order so a reader can match a nerve by name. Latencies are in ms, amplitudes in mV (motor) or µV (sensory) unless otherwise noted, and conduction velocities in m/s.

Upper limb motor NCS

Normal values

Nerve	Root	Latency (max, ms)	Amplitude (min)	NCV (min, m/s)	F-wave (max, ms)
Median to Abd Pol (APB)	C8, T1	4.5	4 mV	50	32
Median to Flex Carp Rad	C6, 7, 8	3.6	2.3 mV	—	—
Median to Flex Pol Long (ant interosseous)	C7, 8, T1	4	2.5 mV	—	—
Median to Pron Quadrat (ant interosseous)	C7, 8, T1	5	1.5 mV	—	—
Median to Pron Teres	C6, 7	3.5	3 mV	—	—
Median to 1st Lumbrical	C8, T1	4.5	0.8 mV	—	—
H Reflex to Flex Carp Rad	C6, 7, 8	19	0.8 mV	—	—
Ulnar to Abd Dig Minimi	C8, T1	3.7	6 mV	50	32
Ulnar to palmer interosseous	C8, T1	4	3 mV	—	—
Ulnar to 1st dorsal interosseous	C8, T1	4.7	5 mV	—	—
Radial to Ext Dig Communis	C7, 8	3.5	4.5 mV	—	—
Radial to Ext Indicis	C7, 8	2.5	1.7 mV	23	—
Suprascapular to Supra & Infraspinatus	C5, 6	Supra 4.3 / Infra 4.8	1.5 mV	—	—
Thoracodorsal to Latissimus	C6, 7, 8	2.7	1.5 mV	—	—
Axillary	C5, 6	5.4	4.6 mV	—	—
Long Thoracic	C5, 6, 7	4.8	—	—	—
Musculocutaneous to Biceps	C5, 6	5.5	4 mV	—	—
Phrenic to Diaphragm	C3, 4, 5	8	300 µV	—	—

Recording & stimulation technique

Nerve	Active electrode	Reference	Ground	Stimulation
Median to Abd Pol (APB)	Halfway between the midpoint of the distal wrist crease and the first MCP joint.	Slightly distal to the first MCP joint.	Between active electrode and the cathode.	A – cathode placed 8 cm proximal to the active electrode, slightly medial to the tendon of the flexor carpi radialis. B – medial to the tendon of the biceps at the elbow, slightly proximal to the antecubital crease.
Median to Flex Carp Rad	Over the belly of the flexor carpi radialis, one third of the distance from the medial epicondyle to the radial styloid.	Over the radial styloid.	On the dorsum of the hand.	Medial to the tendon of the biceps at the elbow, slightly proximal to the antecubital crease.
Median to Flex Pol Long (ant interosseous)	On the lateral forearm, 10.2 cm from the distal wrist crease.	Over the distal tendon of the flexor pollicis longus.	Between the stimulating and recording electrodes.	Medial to the tendon of the biceps at the elbow, slightly proximal to the antecubital crease.
Median to Pron Quadrat (ant interosseous)	Midpoint between the radius and ulna on the dorsal forearm, 3 cm proximal to the ulnar styloid.	Over the radial styloid.	On the dorsum of the hand.	Medial to the tendon of the biceps at the elbow, slightly proximal to the antecubital crease.
Median to Pron Teres	An equilateral triangle is imagined, with the medial epicondyle and the biceps tendon (at the level of the epicondyle) as two of its points. The active electrode is placed at the third point, on the proximal forearm.	Over the radial styloid.	On the dorsum of the hand.	Medial to the tendon of the biceps at the elbow, slightly proximal to the antecubital crease, 10 cm above active electrode.
Median to 1st Lumbrical	On the palm, slightly radial to the long flexor tendon of the index finger (localized by flexion of the index finger) and 1 cm proximal to the midpalmar crease.	At the base of the index finger.	Between active electrode and the cathode.	The cathode is placed 8 cm proximal to the active electrode, slightly ulnar to the tendon of the flexor carpi radialis.
H Reflex to Flex Carp Rad	Over the belly of the flexor carpi radialis, one third of the distance from the medial epicondyle to the radial styloid.	Over the brachioradialis, 3 cm below elbow.	Between the stimulating and recording electrodes.	Medial to the tendon of the biceps at the elbow, slightly proximal to the antecubital crease, 10 cm above active electrode; frequency not more than 0.5 Hz, minimal stimulus to avoid M response and F wave. Cathode is proximal, anode is distal.
Ulnar to Abd Dig Minimi	On the ulnar surface of the hypothenar eminence, halfway between the level of the pisiform bone and the 5th metacarpophalangeal joint.	Slightly distal to the 5th metacarpophalangeal joint.	Between the stimulating and recording electrodes.	A – 8 cm proximal to the active electrode, in a line measured slightly radial to the tendon of the flexor carpi ulnaris. B – 4 cm distal to the medial epicondyle. C – 10 cm proximal to stimulation point B. D – axilla, 10 cm proximal to stimulation point C.
Ulnar to palmer interosseous	On the palm, slightly radial to the midpoint of the third metacarpal.	Slightly distal to third MCP joint.	Dorsum of the hand.	8 cm proximal to the active electrode, slightly radial to the tendon of the flexor carpi ulnaris.
Ulnar to 1st dorsal interosseous	On the dorsum of the first web space, in the center of the triangle formed.	Slightly distal to the fifth MCP joint.	Dorsum of the hand.	8 cm proximal to the active electrode, slightly radial to the tendon of the flexor carpi ulnaris.
Radial to Ext Dig Communis	By grasping the radius and ulna of the subject’s pronated forearm with the thumb and middle finger at the junction of the upper third and middle third of the forearm. The index finger is placed halfway between these two points to identify the extensor digitorum communis.	Ulnar styloid process.	Between the stimulating and recording electrodes.	A – lateral to the tendon of the biceps at the elbow, as it crosses the flexor crease. B – axilla.
Radial to Ext Indicis	4 cm proximal to the ulnar styloid, over the motor point of the extensor indicis.	Ulnar styloid process.	—	A – 8 cm proximal to the active electrode. B – 8 cm proximal to the lateral epicondyle, over the radial groove.
Suprascapular to Supra & Infraspinatus	Supraspinatus, 2 cm above the midpoint of the spine of the scapula. Infraspinatus, 2 cm inferior to the midpoint of the spine of the scapula.	On the midline thoracic spine at the same level.	On the acromion.	Erb’s point.
Thoracodorsal to Latissimus	On the posterior axillary line at the level of the inferior pole of the scapula.	On the ipsilateral flank.	On the ipsilateral lateral chest wall.	Axilla with arm abducted 90°.
Axillary	Most prominent portion of the middle deltoid.	Junction of the deltoid muscle and its tendon.	On the acromion.	Erb’s point — the cathode is placed slightly above the upper margin of the clavicle, lateral to the clavicular head of the sternocleidomastoid muscle. The anode is superomedial.
Long Thoracic	A concentric needle electrode (R) is placed at the digitation of the serratus anterior along the midaxillary line over the 5th rib.	—	Anterior axillary line over the 12th rib level.	Erb’s point.
Musculocutaneous to Biceps	Just distal to the midportion of the biceps brachii muscle.	Proximal to the antecubital fossa, at the junction of the muscle fibers and the biceps tendon.	On the acromion.	Erb’s point.
Phrenic to Diaphragm	5 cm superior to the tip of the xiphoid process.	Over the upper chest.	—	Stimulation is applied at the posterior border of the sternocleidomastoid muscle in the supraclavicular fossa, with the cathode approximately 3 cm superior to the clavicle.

Upper limb sensory NCS

Normal values

Nerve	Root	Latency (onset, ms)	Amplitude (min)	NCV (min, m/s)	F-wave (max, ms)
Median to 2nd, 3rd digits	C6, 7	A: 3.2 / B: 1.8	10 µV	—	—
Median Palmer Cut.	C6	1.7	10 µV	—	—
Ulnar to 5th digit	C8	A: 3.2 / B: 1.8	6 µV	—	—
Radial to thumb	C6	2.2	6 µV	—	—

Recording & stimulation technique

Nerve	Active electrode	Reference	Ground	Stimulation
Median to 2nd, 3rd digits	A ring electrode is placed in the digit being tested, slightly distal to the base of the digit.	4 cm distal to active electrode.	Between active & reference electrode.	A – 14 cm proximal to the active electrode, slightly medial to the tendon of the flexor carpi radialis. B – cathode is placed at the midpoint of the line from the active electrode to stimulation point A.
Median Palmer Cut.	Halfway between the midpoint of the distal wrist crease and the 1st MCP joint.	Slightly distal to the 1st MCP joint.	Between active & reference electrode.	8 cm proximal to the active electrode, slightly medial to the tendon of the flexor carpi radialis.
Ulnar to 5th digit	A ring electrode is placed in the digit being tested, slightly distal to the base of the digit.	4 cm distal to active electrode.	Between active & reference electrode.	A – 14 cm proximal to the active electrode, slightly radial to the tendon of the flexor carpi ulnaris. B – cathode is placed at the midpoint of the line from the active electrode to stimulation point A.
Radial to thumb	Over the radial sensory nerve as the nerve passes over the extensor pollicis longus tendon.	4 cm distal to active electrode.	Between active & reference electrode.	10 cm proximal to the active electrode on the radial side of the forearm.

Lower limb motor NCS

Normal values

Nerve	Root	Latency (max, ms)	Amplitude (min)	NCV (min, m/s)	F-wave (max, ms)
Femoral to Quadriceps	L2, 3, 4	A: 8.5 / B: 7.5	0.5 mV	—	—
Peroneal to Ext Dig Brevis	L5, S1	6.5	1.2 mV	40	60
Tibial to Abductor Hallucis	S1, S2	6	4 mV	40	60
Tibial to Flex Dig Min Brevis	S1, S2	8	1.2 mV	—	—
H reflex to Calf muscle	S1	35	—	—	—

An accessory peroneal nerve is commonly present (20–25% incidence). The accessory peroneal nerve passes behind the lateral malleolus to innervate the extensor digitorum brevis. Its presence should be suspected if the amplitude to proximal stimulation is greater than on ankle stimulation. Its presence can be confirmed by stimulating behind the lateral malleolus. If a response is recorded from the extensor digitorum brevis, an accessory peroneal nerve is present.

Recording & stimulation technique

Nerve	Active electrode	Reference	Ground	Stimulation
Femoral to Quadriceps	Center of vastus medialis.	Quadriceps tendon near the patella.	Between active & reference electrode.	Needle electrode is used. A – superior to the inguinal ligament just lateral to the femoral artery. B – inferior to the inguinal ligament and lateral to the femoral artery.
Peroneal to Ext Dig Brevis	On extensor digitorum brevis muscle on the dorsum of the foot.	5th MCP.	Between active & reference electrode.	A – 8 cm proximal to the active electrode, slightly lateral to the tibialis anterior tendon. B – posterior and inferior to the fibular head.
Tibial to Abductor Hallucis	Medial foot, slightly anterior and inferior to the navicular tubercle (at the most superior point of the arch).	1st MCP.	Between active & reference electrode.	A – posterior to the medial malleolus. B – mid-popliteal fossa.
Tibial to Flex Dig Min Brevis	Midpoint of inferolateral edge of 5th metatarsal.	5th MCP.	Between active & reference electrode.	Posterior to the medial malleolus.
H reflex to Calf muscle	On the back of leg, midpoint between popliteal crease and posterior calcaneus.	Posterior calcaneus.	Between active & reference electrode.	Mid-popliteal crease with the anode distal.

Lower limb sensory NCS

Normal values

Nerve	Root	Latency (onset, ms)	Amplitude (min)	NCV (min, m/s)	F-wave (max, ms)
Lateral Cutaneous n.	L2, 3	A: 3 / B: 3.6	6 µV	—	—
Deep Peroneal	L5	3.7	3.4 µV	—	—
Tibial	—	3	—	—	—
Saphenous nerve	L3, 4	3.8	2 µV	—	—
Sural nerve	S1, 2	3.6	4 µV	—	—

Recording & stimulation technique

Nerve	Active electrode	Reference	Ground	Stimulation
Lateral Cutaneous n.	Along a line connecting the ASIS to the lateral border of the patella with the active electrode (A) 17–20 cm distal to the ASIS.	3 cm distal to the active electrode.	Between active & reference electrode.	A – below the inguinal ligament, 1 cm medial to the line between the ASIS and the lateral border of the patella. B – above the inguinal ligament, 1 cm medial to the ASIS.
Deep Peroneal	Interspace between the 1st and 2nd metatarsal heads.	3 cm distal to the active electrode, on the 2nd digit.	Between active & reference electrode.	12 cm proximal to active electrode and just lateral to the extensor hallucis longus tendon.
Tibial	Over the tibial nerve just proximal to the flexor retinaculum.	3 cm distal to the active electrode.	Between active & reference electrode.	14 cm distal to the active recording electrode.
Saphenous nerve	Proximal and slightly medial to the tibialis anterior tendon.	Slightly anterior to the highest prominence of the medial malleolus.	Between active & reference electrode.	14 cm proximal to the active electrode, deep to the medial border of the tibia.
Sural nerve	Behind the lateral malleolus.	3 cm distal to the active electrode.	Between active & reference electrode.	14 cm proximal to the active electrode in the midline or slightly lateral to the midline of the posterior lower leg.

Cranial nerves NCS

Normal values

Nerve	Root	Latency (onset, ms, max)	Amplitude (min)
Facial nerve	—	Nasalis 3.5; orbicularis oculi 3.8	>50% side-to-side difference is significant; >90% indicates surgery
Cranial accessory	—	3	3 mV
Great auricular nerve	—	1.6	—
Blink reflex	—	Direct latency 4; ipsilateral R1 13; ipsilateral R2 40; contralateral R2 41	R/D ratio (R1 latency to direct response latency) should be 2.6–4.6

Recording & stimulation technique

Nerve	Active electrode	Reference	Ground	Stimulation
Facial nerve	Nasalis, on the lateral mid-nose. The subject may “wrinkle the nose” and the electrode is placed on the most prominent bulge of the muscle. Orbicularis oculi under the eye in line with the pupil (an alternate position is at the lateral border of the eye). Orbicularis oris lateral to the angle of the mouth.	On the tip or bridge of the nose.	Over the base of the neck or on the cheek.	Preauricular stimulation is performed with the cathode just anterior to the lower ear over the substance of the parotid gland and several centimeters superior to the angle of the mandible. Postauricular stimulation is performed by placing the cathode just behind the lower ear, below the mastoid process and behind the neck of the mandible. The anode is posterior.
Cranial accessory	Over the upper trapezius, about 9 cm lateral to the 7th spinous process.	3 cm lateral to the active electrode.	Between the stimulating and recording electrodes.	In the posterior triangle of the neck, 1–2 cm posterior to the posterior border of the sternocleidomastoid muscle and slightly above the midpoint of this muscle. This is a point halfway between the mastoid process and the suprasternal notch. The anode is superior.
Great auricular nerve	On the back of the ear lobe.	2 cm above the active electrode.	On the back of the neck.	8 cm from the active electrode along the lateral border of the sternocleidomastoid muscle, with the cathode superior.
Blink reflex	Over the lower lateral orbicularis oculi muscle bilaterally.	Over the temple or the lateral surface of the nose above the nasalis muscle.	Under the chin or on the forehead or cheek.	Cathode (C) over the supraorbital nerve at the supraorbital notch; the anode is superolateral. A ratio of R1 latency (R) to the direct response latency (D) can be calculated; this R/D ratio should not fall outside the range of 2.6 to 4.6. A larger ratio, with a normal D, is indicative of slowing of the trigeminal portion. If the R/D ratio is low, it is indicative of slowing of the facial nerve. A glabellar tap with a special hammer can be used instead of electrical stimulation. Several blink responses should be tested and the shortest latencies chosen. Latency should be measured to the first deflection from the baseline.

Ahmed Koriesh, MD