Electromyography (EMG) is a diagnostic procedure used to assess the health of muscles and nerves. It is comprised of two components. 

The first is the Nerve Conduction Study (NCS) which studies the quality and general health of the nerve. It involves applying a small electric stimulus to the surface of the skin and recording the signal on surface electrodes in order to measure the speed and strength of the nerve.

The second portion of the test is the needle EMG. It involves using an accupuncture sized pin which is inserted into several different muscles in order to assess the electrical activity of that muscle.

Using both components of the test, the EMG can reveal dysfunctions of the nerve, muscle, and neuromuscular junction.