An EMG (electromyography) test is a diagnostic procedure that assesses the health of muscles and the nerve cells that control them (motor neurons) . It is a form of electrodiagnostic testing that measures the electrical activity of muscles and nerves. An EMG test can be used to diagnose a wide variety of neuromuscular diseases, motor problems, nerve injuries, or degenerative conditions, such as amyotrophic lateral sclerosis (ALS), carpal tunnel syndrome, and other conditions that affect one nerve. The test can reveal nerve dysfunction, muscle dysfunction, or problems with nerve-to-muscle signal transmission. During a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle. A nerve conduction study (NCS), another part of an EMG, uses electrode stickers applied to the skin (surface electrodes) to measure the speed and strength of signals traveling between two or more points. EMG tests and nerve conduction studies can both help find out if you have a disorder of your muscles, nerves, or both. These tests can be done separately, but they are usually done at the same time. Your doctor may order an EMG test if you experience symptoms such as muscle weakness or tingling.