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Electromyography by Editorial Staff and Contributors

Definition | Reasons for Test | What to Expect | Results | Call Your Doctor

Definition

Electromyography (EMG) measures and records the electrical activity of a muscle. The test can record a muscle's electrical activity at rest or during a muscle contraction.

An EMG is often done with nerve conduction studies . These studies can analyze the electrical activity in your nerves.

EMG of the Shoulder

Reasons for Test

EMG is most often done to:

Aid in diagnosing the source of pain, cramping, or weakness in the muscles and nerves
Differentiate between true muscle weakness and limitations due to pain
Determine if muscles are working properly
Distinguish between muscle and nerve disorders

What to Expect

Prior to Test

Make sure you talk to your doctor about the medicines you are taking. You may be asked to adjust certain medicines up to a week before the test, such as:

Anti-inflammatory drugs (eg, aspirin )
Blood thinners, such as clopidogrel (Plavix), warfarin (Coumadin), or ticlopidine (Ticlid)

On the day before and day of the test:

If you have myasthenia gravis , ask if you should take any medicine before the test.
If directed to, avoid cigarettes, coffee, tea, and soft drinks for 2-3 hours before the test.
Take a bath or shower before the test.
On the day before, do not use lotion or oil.
Wear comfortable clothing, but expect to change into a hospital gown.
Tell your doctor if you have a pacemaker or other implanted device.

Description of the Test

A small needle electrode will be inserted into a muscle at rest. You will be asked to rest or contract the muscle. The electrical activity picked up by the needle will produce a waveform. The waveform will be recorded and analyzed. The test is repeated on different muscles and limbs.

After Test

You will be able to leave once the test is done. Once you are home:

Resume any medicine you stopped before the test.
Resume normal activities as tolerated.

How Long Will It Take?

30-90 minutes

Will It Hurt?

You may have some pain when the needle electrodes are inserted. The insertion feels like an injection into the muscle.

After the test, you may have muscle aches and discomfort for several days. Warm compresses and pain medicine may help.

Results

The doctor doing the EMG may discuss the results with you. A report will also be sent to your regular doctor. Your doctor will discuss treatment options based on the tests and other factors.

Call Your Doctor

After the test, call your doctor if any of the following occurs:

Signs of infection, including fever and chills
Redness, swelling, increasing pain, excessive bleeding, or discharge around the needle sites

RESOURCES:

National Institutes of Health http://www.nih.gov/
National Institute of Neurological Disorders and Stroke http://www.ninds.nih.gov/

CANADIAN RESOURCES:

Health Canada http://www.hc-sc.gc.ca/
Muscular Dystrophy Canada http://www.muscle.ca/

References:

Medical encyclopedia: electromyography. National Library of Medicine website. Available at: http://www.nlm.nih.gov/medlineplus . Accessed August 1, 2003.
What to expect during your EMG test. American Association of Neuromuscular & Electrodiagnostic Medicine website. Available at: http://www.aanem.org/index.cfm? . Updated March 2005. Accessed June 5, 2008.
Young RR, Hutton JT, Homan RV. Gait and movement disorders. American Academy of Neurology website. Available at: http://www.aan.com/familypractice/html/chp8.htm . Accessed June 5, 2008.

Last reviewed July 2010 by Robert E. Leach, MD

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