Electromyogram (EMG) for Diagnosis | Medstar Health

An electromyogram (EMG) measures the electrical activity in muscles, at rest and during contraction. Some patterns of electrical activity indicate a disease of the nerves or muscles. It is done to detect certain nerve and muscle disorders that cause weakness, paralysis, and/or twitching of the muscles. An EMG usually lasts 30 to 60 minutes.

Nerve conduction studies are often done along with an EMG. Nerve conduction studies measure how well and how fast the nerves can send electrical signals to the muscles. During this test, low-voltage electrical shocks are used to stimulate the nerves, which in turn stimulate the muscle. The test records the ability of the nerve to send the impulse to the muscle.

Abnormal results suggest a person may be suffering from a disease that damages the muscles or nerves.

EMG for diagnosis

EMG and nerve conduction studies can help diagnose diseases that damage muscle tissue, nerves, or the junctions between nerves and muscles, such as:

An EMG takes approximately 30 to 60 minutes, and a nerve conduction study can take anywhere from 15 minutes to one hour, depending on how many areas are being tested.

Preparing for an EMG

One week prior to your EMG, your doctor will give you specific instructions regarding your medications and any effects they might have against the test. About three hours before the test, you will not smoke or consume any caffeinated products. Patients are advised to wear comfortable, loose fitting clothing to their EMG. In some cases, a hospital gown is provided for the test.

During the EMG

In order to relax your muscles, the EMG is performed with you lying down or reclining. A special soap will be used to clean the areas of your skin being tested, and needle electrodes will be applied to those muscles.

Electrical activity will first be recorded of your muscles at rest. Your technician will then ask you to contract your muscles, and the resulting electrical activity will be recorded. The electrodes might be moved to different muscles or different portions of your muscles during the EMG. Your muscles’ electrical activity will be displayed on a special video screen; it might also be recorded on video.

After the EMG

After your EMG, the electrodes are removed from your muscles, and your skin in the tested areas is cleaned. You may be prescribed medication for soreness in the tested areas. Soreness and tingling in the muscles is common for 1 to 2 hours following an EMG.

While full results will not be available until 2 or 3 days later, you will be able to find out preliminary results immediately after the test.


Electromyogram (EMG) is an extremely safe procedure. There is a slight chance of swelling or bruising wherever the needles were placed, and chances of infection are minimal.

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