An electromyogram (EMG) measures the electrical activity generated by muscles at rest and during muscle contraction.  Unlike nerve conduction studies (NCS), there is no electrical stimulation applied by the testing physician.  It is strictly a recording procedure.  The electrical activity is recorded by a thin, flexible, Teflon-coated needle with a special recording tip.  The EMG needle looks much like an acupuncture needle, but with a special recording function.  The needle tip is placed a short distance into the muscle to be tested. Patients may experience a mild pinch, sting or burn with testing, but the discomfort is very temporary.  A sterile, disposable needle is used, so that there is essentially no risk of infection.

The electrical signals that are generated by normal muscle at rest and with activity differ from those seen when there is injury to the peripheral nerves or the spinal nerve roots that supply that muscle.   Changes are also seen when disease involves the muscle itself.

The examining physician uses an expert knowledge of muscle and nerve anatomy to determine the source and the location of injury or disease.  This is useful in diagnosing injury to muscle and nerve structures and to determine the cause of muscle weakness, paralysis or muscle twitching.  EMG testing can determine the relative age of neuromuscular injury and provide useful information about prognosis for recovery.

EMG testing is extremely safe for the patient.  There may be some temporary discomfort during or after the testing, but it is temporary and no after effects can be expected.  There is no need to fast beforehand and it is not necessary to hold medications prior to the test.  There are no activity restrictions that need to be followed before or after testing.  You should notify the physician performing the EMG test if you are on blood thinners.  The risk for bleeding is increased, but this usually does not prevent the test from being completed safely.