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Nerve conduction velocity (NCV) test–also called a nerve conduction study (NCS)–is a measurement of the speed of conduction of an electrical impulse through a nerve. NCV can determine nerve damage and destruction.

During the test, the nerve is stimulated, usually with surface electrode patches attached to the skin. Two electrodes are placed on the skin over the nerve. One electrode stimulates the 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 nerve conduction velocity (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 electromyography (EMG). An EMG measures the electrical activity in muscles and is often performed at the same time as NCV. Both procedures help to detect the presence, location, and extent of diseases that damage the nerves and muscles.