Electromyograph

An instrument that detects and records the electrical activity produced by muscles as they contract, using either fine needle electrodes inserted into the muscle or electrodes placed on the skin above it, to help diagnose disorders of the muscles or of the nerves that control them. The resulting signal, displayed as a trace and often made audible as well, shows patterns that differ depending on whether a muscle is at rest, contracting normally, or affected by disease of the muscle fibers themselves or of the motor nerves that activate them, letting a physician distinguish between these possibilities. Early laboratory instruments for recording muscle electrical activity were built in the first half of the twentieth century, and the technique became a standard clinical tool in neurology from the middle of the century onward as amplifiers, electrodes, and recording equipment grew reliable and compact enough for routine use in a clinic. Electromyography is commonly paired with nerve conduction studies, which measure how quickly a signal travels along a nerve, so that the two techniques together can localize damage to a particular nerve, muscle, or the junction between them.