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Why it's done
By Mayo Clinic staffThe activity of your muscles and the nerves that control them produce electrical signals. A healthy, relaxed muscle is electrically silent. When you contract your muscle, the nerves create a pattern of electrical signals that cause your muscle to respond. An EMG records this electrical pattern.
If the electrical pattern is abnormal when the muscle is at rest or when a nerve is stimulated, it may indicate a problem with the nerve or muscle. Results from an EMG can help diagnose a condition that interferes with muscle contractions. These conditions include:
- Diseases that affect the muscle, such as muscular dystrophies
- Diseases that affect the connection between the nerve and the muscle (neuromuscular junction), such as myasthenia gravis
- Diffuse nerve disorders that cause peripheral neuropathy
- Disorders that affect the motor neurons (anterior horn cells) in the spinal cord, such as amyotrophic lateral sclerosis or a ruptured spinal disk
To provide a more complete picture of your nerve function, an EMG is done in conjunction with a nerve conduction study. Using electrodes on the surface of your skin, this test measures the strength and speed of the electrical signals as they travel through your nerves to the muscles. Used along with an EMG, nerve conduction studies can help diagnose disorders that affect nerve function, such as Charcot-Marie-Tooth disease.
