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EMG Information


Electromyography (EMG) measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle. The test is used to help detect neuromuscular abnormalities. During the test, one or more thin acupuncture like needles (also called electrodes) are inserted through the skin into the muscle. The electrical activity picked up by the electrodes is then displayed on an oscilloscope (a monitor that displays electrical activity in the form of waves). An audio-amplifier is used so the activity can be heard. EMG measures the electrical activity of muscle during rest, slight contraction and forceful contraction. Muscle tissue does not normally produce electrical signals during rest. When an electrode is inserted, a brief period of activity can be seen on the oscilloscope, but after that, no signal should be present.

After an electrode has been inserted, you may be asked to contract the muscle, for example, by lifting or bending your leg. The action potential (size and shape of the wave) that this creates on the oscilloscope provides information about the ability of the muscle to respond when the nerves are stimulated. As the muscle is contracted more forcefully, more and more muscle fibers are activated, producing action potentials..


  • You will be asked to sit or lie down for the test.

  • A neurologist will locate the muscle(s) to be studied.

  • The skin will be cleansed with an antiseptic solution. Next, a fine, sterile needle will be inserted into the muscle. A ground electrode will be positioned under your arm or leg.

  • Five or more needle insertions may be necessary for the test. You may experience slight pain with the insertion of the electrode, but it is usually painless.

  • If the test is painful you must tell your examiner because this can interfere with the results.

  • You will be asked to relax and then perform slight or full-strength muscle contractions.

  • The electrical activity from your working muscle will be measured and displayed on the oscilloscope.

  • An audio amplifier may also be used so that both the appearance and sound of the electrical potentials can be evaluated. If the recorder is attached to an audio amplifier, you may hear a sound like hail on a tin roof when you contract your muscle.


  • Some muscle soreness may persist for a day or so following the procedure. Notify your doctor if you experience increasing pain, tenderness, swelling, or pus at the needle insertion sites.Your physician may give you additional or alternate instructions after the procedure, depending on your particular situation.

Citation: Electromyography . Retrieved from

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