Electromyogram
(EMG)

Medical Author: William C. Shiel Jr., MD, FACP, FACR
Medical Editor: Melissa Conrad Stöppler, MD

• What is an electromyogram?
• Why is an EMG test done?
• How is an intramuscular EMG done?
• How do you prepare for an intramuscular EMG?
• Does an EMG hurt?
• What other test is done during an intramuscular EMG?

What is an electromyogram?

An electromyogram (EMG) is a test that is used to record the electrical activity of muscles. When muscles are active, they produce an electrical current. This current is usually proportional to the level of the muscle activity. An EMG is also referred to as a myogram.

EMGs can be used to detect abnormal electrical activity of muscle that can occur in many diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves, peripheral nerve damage (damage to nerves in the arms and legs), amyotrophic lateral sclerosis (ALS), myasthenia gravis, disc herniation, and others.

Why is an EMG test done?

An EMG is often performed when patients have unexplained muscle weakness. The EMG helps to distinguish between muscle conditions in which the problem begins in the muscle and muscle weakness due to nerve disorders. The EMG can also be used to detect true weakness, as opposed to weakness from reduced use because of pain or lack of motivation. EMGs can also be used to isolate the level of nerve irritation or injury.

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