G1 active recording electrode
G1: APB motor point
Place G1 over the center of the APB motor point, about one-third of the distance from the metacarpal–carpal crease to the thumb MCP joint.
Table 2 · p.373 ↗
Motor study
Upper limb
Median motor nerve conduction study
Place G1 over the APB motor point; use routine wrist and elbow stimulation, with optional palm stimulation for the CTS wrist–palm segment and optional axilla stimulation for proximal localization.
01 · Placement
G1, G2, stimulation and ground landmarks
G2 reference electrode
G2: first MCP joint, 4–5 cm distal to G1
Place G2 on the first MCP joint, 4–5 cm distal to G1 and completely off the APB muscle over its distal tendon.
Distance · 4–5 cm distal to G1
Median motor technique · p.32 ↗Optional CTS stimulation site
Optional palm stimulation: 3 cm distal to wrist crease
For the optional CTS wrist–palm segment, stimulate the median nerve in the central palm 3 cm distal to the wrist crease and 5–6 cm distal to S2; keep the stimulator aligned with the median nerve and avoid co-stimulating the ulnar nerve.
Distance · 3 cm distal to wrist crease; 5–6 cm distal to S2
CTS Table 4 · p.S934 ↗Stimulation site
Wrist stimulation: between FCR and PL tendons
Stimulate on the volar wrist 8 cm proximal to G1 between the flexor carpi radialis and palmaris longus tendons; orient the cathode toward G1.
Distance · 8 cm from G1
Table 2 · p.373 ↗Stimulation site
Elbow stimulation: medial to the brachial artery pulse
Stimulate in the antecubital fossa immediately medial to the brachial artery pulse, between the distal biceps tendon and medial epicondyle.
Distance · Variable—measure the S2–S3 segment on the patient
Table 2 · p.373 ↗Optional proximal stimulation site
Optional axilla stimulation: proximal median nerve
For optional proximal localization, stimulate high in the medial arm/axilla over the proximal median nerve beside the axillary pulse; measure the S3–S4 segment on the patient.
Distance · Variable—measure the S3–S4 segment on the patient
Proximal median localization · p.34 ↗Ground region
Ground electrode region
Place the ground on the volar forearm between the wrist stimulation site and the APB recording electrodes.
Table 2 · p.373 ↗02 · Reference values
Adult normal limits
| Measure | Reference limit | Basis |
|---|---|---|
| Distal CMAP amplitude | ≥4.1 mV | 3rd percentile lower limit |
| Conduction velocity | ≥49 m/s | 3rd percentile lower limit |
| Distal motor latency | ≤4.5 ms | 97th percentile upper limit |
03 · Technique
Acquisition conditions
Fixed distance
G1 to wrist (S2): 8 cm; optional palm–wrist segment: 5–6 cm; measure proximal segments on the patient
Limb position
S1 palm is optional for CTS; S4 axilla is optional for suspected proximal localization
Sensitivity
5 mV/div
Sweep
2 ms/div
Filter
2–3 Hz–10 kHz
Temperature
Maintain dorsal hand skin temperature >32°C
Ground
Place the ground between the stimulating and recording electrodes
Primary evidence
Method-matched AANEM reference data
Adult median motor reference values; see the source table for age- and sex-stratified limits.