Electromyography tests nerves the same way an electrician would test a wire. Since nerves operate by conducting electrical impulses, the easiest way to see if they are damaged is to send a current through a nerve from one end to see if it reaches the other. If the current reaches the other point at full strength, there is no damage to the nerve. If the impulse is reduced, or does not come through at all, there may be damage to the nerve.
At the beginning of the procedure, the patient lays on a table with the EMG machine beside him or her. In the first part of the procedure, known as “nerve conduction study,” a set of electrodes will be placed on the skin somewhere on the joint or limb to be studied; these will be the “receiving” electrodes. The neurologist will then use an electrode to deliver small shocks to the skin at other points. While he does this, the patient may feel a tingling or even slightly painful sensation for the brief amount of time that the doctor administers the procedure.
The second part of the procedure is known as needle examination. During this part of the procedure, the neurologist will insert a needle into the muscle to determine the extent of muscle damage caused by the nerve injury. While lying on the table or sitting in the chair, the patient may feel slight muscular discomfort and may hear a static-like noise while the neurologist measures the amount of activity in the muscle.