Which test is which
EMG vs NCV: What Each Test Shows
They are usually done in the same appointment, which is why people think they are one test. They are not.
An NCV tests the wiring. An EMG tests what the wiring is connected to. They are booked together often enough that most patients arrive thinking they are one test — and then are surprised by the needle.
NCV — nerve conduction study
Small surface electrodes are taped to the skin, and a brief pulse is delivered along the path of a nerve. The machine measures how fast the signal travels and how strong it is when it arrives.
Speed and strength answer different questions. A signal that arrives late points towards the insulation around the nerve fibre; one that arrives on time but faint points towards the fibres themselves. The pulse feels like a tap or a tingle, and nothing is put into you.
EMG — electromyography
A fine needle electrode is placed into the muscle, and the machine listens to the muscle's own electrical activity — at rest, and while you tense it gently.
This is the one study where some discomfort is normal. It is brief, and it shows something no surface electrode can: whether a weak muscle is weak because its nerve supply is failing, or because of a problem in the muscle itself.
Why they are usually done together
Because between them they separate the possibilities. Take weakness and numbness in a hand. NCV can show where along the nerve the signal is being held up; EMG can show whether the muscles that nerve serves have been affected yet, and roughly for how long. One test without the other frequently leaves the question half-answered, which is why a referral for "NCV" often ends up as both.
Your neurologist decides how much is examined — one limb, or several — from the examination and your symptoms. That decision is also what makes one study a bigger piece of work than another; see test prices and what is included.
What to expect on the day
Come with clean skin and no oil or lotion on the arms and legs, and wear something loose enough to expose the limb being tested. Continue your regular medicines, but tell us if you take blood thinners or have a pacemaker or other implanted device — both change how the study is done.
Allow around 30–60 minutes depending on how much is being examined. There is no recovery time. The recording is reviewed by our specialist and the report is shared with you or your referring doctor.
The related studies
Some questions need a more specific test: single-fibre EMG and RNST look at the junction between nerve and muscle, and the blink reflex study examines the facial nerve pathway. If you are not sure which you need, book a consultation first — the examination decides the test, not the other way round.