- Electromyography (EMG): This test measures the electrical activity of muscles and is used to diagnose problems with the nerves or muscles. For surface EMG, electrodes are filed with a conductive gel and taped to the skin. Needle EMG involves inserting a needle into a muscle to record the electrical activity. Single fiber EMG uses specialized needles that allow recording from single muscle fibers. The needle is inserted into a muscle and the subject is asked to tense that muscle slightly.