These tests are often used to evaluate patients with numbness, weakness or limb pain.  The commonly are used to diagnose such disorders as carpel tunnel syndrome, radiculopathies and other nerve diseases or injuries.

Nerve Conduction Velocity (NCV) test 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 with a mild electrical impulse and a separate electrode taped on the skin records the nerve impulse that is generated. 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.