Definition of Electromyogram

Electromyogram: A test used to record the electrical activity of muscles. When muscles are active, they produce an electrical current that is usually proportional to the level of muscle activity. An electromyogram (EMG) is also called a myogram.

The EMG can detect abnormal muscle electrical activity in many diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves, peripheral nerve damage (damage to nerves in the arms and legs), amyotrophic lateral sclerosis (ALS) (also known as Lou Gehrig disease), myasthenia gravis, disc herniation, and others. The EMG helps to distinguish between muscle conditions in which the problem begins in the muscle and muscle weakness due to nerve disorders.

There are two types of EMG -- the intramuscular EMG and the surface EMG. Intramuscular EMG (the most commonly used type) involves inserting a needle electrode through the skin into the muscle whose electrical activity is to be measured. Surface EMG (SEMG) involves placing the electrodes on (not into) the skin overlying the muscle to detect the electrical activity of the muscle. In both types of EMG, the electrical activity is displayed visually on an oscilloscope and may also be displayed audibly through a microphone.

The word "electromyography" looks dauntingly long but it is made up of three parts: "electro-" + "-myo-" + "-graphy." ("-myo-" is from the Greek "mys", meaning muscle and "graphy" comes from the Greek "grapho" meaning to write) . So electromyography literally is the writing (recording) of muscle electricity.