Medical Q&As

EMG - why is it done?

What is an EMG study and why is it done?

EMG is an abbreviation for electromyography, which is also referred to as a nerve conduction study. The test measures the response in a muscle to stimulation through a nerve. A needle electrode is inserted through the skin into the muscle much like inserting a needle into a vein for the purpose of taking a blood sample. The electrical activity within the muscle is measured using a special oscilloscope. The person is then instructed to contract the muscle and the wave pattern on the oscilloscope is observed. The wave pattern gives useful information about the ability of the muscle to respond to nervous stimulation. An EMG is usually performed when a person has symptoms of weakness and the physical examination revels that muscle strength is reduced. The test is useful in distinguishing between a primary condition of the muscles or a neurological disorder. For example if the person were suffering from a nerve disease or injury the EMG result would be abnormal because the injured nerve would not transmit a normal signal through to the muscle being tested. In that scenario the muscle weakness would be attributable to the nerve damage rather than being an inherent problem with the muscle. After the test the muscle can feel a little sore or bruised just like after having an intramuscular injection.