URL of this page: //medlineplus.gov/ency/article/003929.htm. Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles. The health care provider will insert a very thin needle electrode through the skin into the muscle. The electrode on the needle picks up the electrical activity given off by your muscles. This activity appears on a nearby monitor, and may be heard through a speaker.