Fig - Muscle Responses

The EMG (electromyogram) is a test that evaluates the electrical activity in nerves and muscles. This test is helpful to determine if abnormalities exist in the way nerves transmit electrical impulses and the effect this has on muscles. The EMG test consists of two parts:

• Nerve Conduction Study (NCS) which evaluates the speed and amount of electrical activity along a nerve.
• EMG study which looks at electrical activity in muscles at rest and also when they are tensed up or constricted (if possible) to determine if the pattern of activity is normal.

Fig - NCS of Foot

The patient will be asked to lie on an examination table. Electrodes are placed on the skin over the nerve to be studied. These electrodes act as microphones to pick up any electrical signal that goes by them. An electrical stimulator is then placed on the skin near the electrodes and is used to create an electrical current strong enough to fully stimulate the nerve. A computer is used to record responses as various nerves are tested. This allows the physician to measure and calculate how fast the nerve is sending the impulses to the muscle. This is called Nerve Conduction Velocity.

Fig - EMG Evaluation

The muscles are assessed by inserting a pin electrode into the muscle with the computer then recording the muscle potential. The sensation is similar to that of an injection that goes into the muscle as the pin electrode is inserted into the muscle. (That is if sensory awareness is not a problem.) It is important for the patient to stay as calm as possible to reduce discomfort and to achieve accurate readings.

Does it hurt?
Parts of the test are uncomfortable but not severely painful. The anxiety before the test can be more of a factor than the test itself. A majority of the time spent with the patient is setting up the studies and running the computer; a very small amount of the time involves electrical stimulation or use of the pin electrode. The electrical stimulation of the nerve conduction study could be compared to a static electricity shock from a doorknob after walking across carpet. The pin insertion could be compared to being pinched by someone's fingernails. (And how do we know this? We have done it on ourselves first!).

Are there any side effects?
Not really, there can be some minor irritation at the pin insertion sites but otherwise, there are no lasting effects from either the NCS or the EMG.