Definition of Electromyography:

Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.

See also: Nerve conduction velocity test

How the test is performed:

The health care provider will insert a very thin needle electrode through the skin into the muscle. The electrode on the needle picks up the electrical activity given off by your muscles. This activity is displayed on a special monitor called an an oscilloscope, and may be heard through a speaker.

After placement of the electrodes, you may be asked to contract the muscle. For example, bending your arm. The presence, size, and shape of the wave form -- the action potential -- produced on the monitor provide information about your muscle's ability to respond when the nerves are stimulated.

A nerve conduction velocity test is usually performed along with an EMG.

How to prepare for the test:

No special preparation is usually necessary. Avoid using any creams or lotions on the day of the test.

How the test will feel:

You may feel some pain or discomfort when the electrodes are inserted, but most people are able to complete the test without significant difficulty.

Afterward, the muscle may feel tender or bruised for a few days.

Why the test is performed:

EMG is most often used when people have symptoms of weakness and examination shows impaired muscle strength. It can help to differentiate primary muscle conditions from muscle weakness caused by neurologic disorders.