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 small 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 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 all of the electrode have 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 abillity 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.
How to prepare before your test
We ask that you wear loose fitting clothing; shorts or a skirt if you are having your lower extremities tested, and short sleeve or sleeveless clothing for upper extremities.
Please do not use any lotions, oils or powders on the skin that is to be tested.
These pages are intended to provide basic information about neurological procedures to the general public. It is not intended to, nor does it, constitute medical advice, and readers are warned against changing medical schedules and activities without first consulting a physician.