Nerve conduction · Beginner
Measure latency, amplitude and velocity
Latency, amplitude & conduction velocity
Reproducible measurements require explicit cursors, distances and units.
01Place the cursors
- Onset latency runs from stimulation to response onset; peak latency ends at the specified peak.
- Motor conduction velocity uses the difference between two onset latencies. Distal motor latency also includes NMJ and muscle depolarization time.
02Calculate
- Motor velocity (m/s) = interstimulus distance (mm) ÷ [proximal − distal onset latency] (ms).
- Example: 240 mm ÷ (8.0 − 3.2) ms = 50 m/s. Measure distance along an appropriate nerve course.
- Specify baseline-to-peak or peak-to-peak SNAP amplitude; their reference limits are not interchangeable.
03Check interpretation
- An initial positive CMAP deflection should prompt review of G1, G2 and volume conduction.
- Duration and area help assess temporal dispersion and phase cancellation.
Pause and explain
Explain in your own words: “Numerically, mm/ms equals m/s. Do not multiply by another 1,000.” Then think of a situation in which it could be misinterpreted.
Show a review prompt
Dividing distal distance by distal motor latency does not give standard segmental motor conduction velocity.
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References and further reading
- Upper and Lower Extremity Nerve Conduction Studies (2023) ↗AANEM · Technical course · Link accessed 2026-09-08
- Electrodiagnostic reference values for upper and lower limb nerve conduction studies in adult populations (2016) ↗AANEM · Evidence-based reference data · Link accessed 2026-09-08
Educational synthesis; independent neuromuscular specialist review is pending. Publication dates and compilation dates are distinct. This is an original teaching synthesis; consult the source for complete methods and criteria.