Electromyography (EMG)

What is it?

An electromyogram (EMG) is a test that measures the electrical activity of a muscle. It detects any signs of blocking or slowing down of responses to nerve stimulation. The test provides information about the muscle itself and shows how well it receives stimulation from the nerve. A nerve conduction velocity (NCV) test is often done at the same time as an EMG.

Why should I do it?

An EMG is often used to evaluate unexplained muscle weakness, twitching or paralysis, and to find the causes of numbness, tingling and pain. EMG testing can differentiate between true weakness and reduced use because of pain or lack of motivation. It can also determine whether a muscle disorder begins in the muscle itself or is caused by a nerve disorder.

How is it performed?

In an EMG, a physician or technician inserts a very fine needle, which serves as an electrode, through the skin into the muscle. With the electrode in place, the patient is asked to slowly contract the muscle—for example, by bending the arm—with gradually increasing force, while the electrical activity is being recorded. The activity can be displayed visually on an oscilloscope or screen, or played audibly through a speaker. The results can provide information about the ability of the muscle to respond to nerve stimulation.

How will it feel?

The patient may feel some minor discomfort, similar to an injection, when the needle or needles are inserted. Afterward, the examined muscle may feel tender or sore for a few days, and there may be a small bruise.