Electro diagnosis is mainly concerned with the electrical activity in voluntary muscles and peripheral nerves including the study of their reaction to electrical stimulation. Electromyography consists of nerve trunk stimulation to determine the thresh hold for excitation and direct muscle stimulation to plot intensity duration curves. This is followed by the insertion of needle electrodes into the muscles to explore for activity at rest and the response to volitional activity. It is combined with motor and sensory nerve stimulation to ascertain latencies, conduction velocities and the possible site of a conduction block.