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
- Differentiate between true muscle weakness and limitations due to pain
- Determine if muscles and nerves are working properly
- Distinguish between muscle and nerve disorders
Problems from the procedure are rare, but all procedures have some risk. Your doctor will review potential problems, like:
- Pain or bruising at the needle insertion site
- Infection at the needs insertion site
What to Expect
Prior to Test
Make sure you talk to your doctor about the medications you are taking. You may be asked to adjust certain medications up to a week before the test, such as:
- Aspirin or other non-steroidal anti-inflammatory drugs (NSAIDs)
- Blood thinners
On the day before and day of the test:
- If you have myasthenia gravis, ask if you should take any medication 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. You will have 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.
You will be able to leave once the test is done. Once you are home:
- Resume any medications you stopped before the test
- Resume normal activities as tolerated
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 medication may help.
Call Your Doctor
After the test, call your doctor if any of the following occur:
- Signs of infection, including fever and chills
- Redness, swelling, increasing pain, excessive bleeding, or discharge around the needle sites
National Institutes of Health
National Institute of Neurological Disorders and Stroke
Muscular Dystrophy Canada
Electromyography (EMG). Johns Hopkins Medicine website. Available at: http://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/electromyography_emg_92,P07656. Accessed July 31, 2013.
FAQ: patient information. American Association of Neuromuscular & Electrodiagnostic Medicine website. Available at: http://www.aanem.org/Education/Patient-Resources/Learn-About-an-EMG.aspx. Accessed July 31, 2013.
Last reviewed June 2013 by John C. Keel, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.