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Overview of electromyography

Steven H Horowitz, MD
Section Editor
Jeremy M Shefner, MD, PhD
Deputy Editor
John F Dashe, MD, PhD


Electromyography (EMG) is the clinical study of the electrical activity of muscle fibers individually and collectively. This electrical activity can be recorded via surface or needle electrodes, the latter being used far more commonly in the clinical setting, and is evaluated during needle insertion, during periods of rest (spontaneous activity), and during periods of voluntary muscle contraction [1].

This topic will review the basic principles of EMG. Detailed discussions of the clinical utility of EMG are presented separately in topic reviews relating to specific diseases. Nerve conductions studies are discussed elsewhere. (See "Overview of nerve conduction studies" and "Nerve conduction studies: Late responses".)


Needle electrodes measure the electric potential difference between two sites. They are usually monopolar or concentric [1].

With the monopolar electrode, the needle serves as the active recording site, and a surface electrode some distance away serves as the reference electrode

In the concentric electrode, which looks like a hypodermic needle, a fine wire in the center serves as the active electrode, with the needle cannula as the reference


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Literature review current through: Sep 2016. | This topic last updated: Sep 17, 2015.
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