What kinds of EMG are there?

There are two types of EMG: intramuscular EMG and surface EMG (SEMG).

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.

Intramuscular EMG is the "classic" form of EMG (and is the main subject here).

How is an intramuscular EMG done?

A needle is inserted through the skin into the muscle. The electrical activity is detected by this needle (which serves as an electrode). The activity is displayed visually on an oscilloscope and may also be displayed audibly through a microphone.

Since skeletal muscles are often large, several needle electrodes may need to be placed at various locations to obtain an informative EMG.

After placement of the electrode(s), the patient may be asked to contract the muscle (for example, to bend the leg).

The presence, size, and shape of the wave form (the action potential) produced on the oscilloscope provide information about the ability of the muscle to respond to nervous stimulation. Each muscle fiber that contracts produces an action potential. The size of the muscle fiber affects the rate (how frequently an action potential occurs) and the size (the amplitude) of the action potential.

How do you prepare for an intramuscular EMG?

For adults, no special preparation is needed. For infants and children, the physical and psychological preparation depends on the child's age, behavior, and prior experience. (For instance, has the child been traumatized by another medical or dental procedure?)

Does an EMG hurt?

Yes. There is some undeniable discomfort at the time the needle electrodes are inserted. They feel like shots (intramuscular injection), although nothing is injected during an EMG. Afterwards, the muscle may feel a little sore for up to a few days.