Electromyography (EMG) is a test that checks the health of muscles and the nerve cells that control them (motor neurons). The electric signals sent by motor neurons make muscles contract. An EMG takes these signals and turns them into graphs, sounds, or numbers that a specialist can read.

An EMG uses tiny devices called electrodes to transmit or detect electrical signals. During an EMG, a needle electrode is put right into a muscle to record the electrical activity in that muscle. The results of an EMG can show problems with nerves, muscles, or the way nerves send signals to muscles.