Electrodiagnostic testing evaluates muscle symptoms that may result from injury or disease to either nerves or muscles in the body. Symptoms can include muscle pain, weakness or numbness. There are two types of electrodiagnostic testing that are commonly used: electromyography, or EMG, and nerve conduction studies. These tests analyze the electrical activity taking place in the nerves and muscles. EMG tests muscle activity; it involves inserting a needle through the skin and into the muscle. The needle records electrical activity in the muscle as the patient relaxes then contracts the muscle. When a normal muscle is at rest, there is no electrical activity; when the muscle contracts, electrical activity is recorded. Nerve conduction studies are usually done along with EMG and record how nerves are functioning. During this procedure, electrodes are taped on the skin surface along the nerve pathway. Electrical signals are then sent along the pathway. Sensors record the electric activity and measure how fast the impulse travels along the nerve pathway. The results are displayed on a computer monitor and are evaluated. Both tests are important tools in evaluating injuries to the nerves or nerve roots as well as diseases of the nerves and muscles.