<qa>  What is the electromyography used to measure electrical activity of muscles?Participants will undergo one or more of the procedures detailed below. Patients test results will be compared with those of normal volunteers. Before each test, participants will provide a medical history and undergo a brief physical examination. During each procedure, the subject will have surface electromyography EMG to measure the electrical activity of muscles. For EMG, electrodes metal discs filled with a conductive gel are taped to the skin over the muscle to be evaluated. 