A nerve conduction velocity (NCV) test — also called a nerve conduction study (NCS) — is a measurement of the speed at which an electrical impulse moves through your nerve. NCV can determine nerve damage.
During the test, your nerve is stimulated, usually with surface electrode patches attached to your skin. Two electrodes are placed on the skin over your nerve. One electrode stimulates your nerve with a very mild electrical impulse and the other electrode records it. The resulting electrical activity is recorded by another electrode. This is repeated for each nerve being tested.
The NCV (speed) is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.
A related procedure that may be performed is an electromyography (EMG). This measures the electrical activity in your muscles and is often performed at the same time as an NCV. Both procedures help to detect the presence, location, and extent of diseases that damage the nerves and muscles.