Electromyography is a test that assesses the health of the muscles and the nerves controlling the muscles.

For an EMG, a needle electrode is inserted through the skin into the muscle. The electrical activity detected by this electrode is displayed on an oscilloscope, and may be heard through a speaker.

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

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

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

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.