An electromyography, or EMG, is a test that is use to determine the health of muscles and to record their activity. Muscles usually produce an electrical current when active, as stated by MedicineNet.
The test is usually carried out when a person is experiencing unexplained weakness of the muscles. This helps to know the true weakness that if affecting the muscles. During the test, the electrical current/signals are translated by an EMG, which features devices called electrodes for detecting and transmitting the signals. The test also allows the strength and speed of the signals to be determined through a process called nerve conduction study, as stated by Mayo Clinic.