Electromyography (EMG)

Electromyography (EMG) is a test that shows how much activity is being produced at each muscle. It is a very technical subject, but the basics of EMG are quite simple to understand. When your body moves a muscle, electricity is produced. Special electrodes are placed ON the skin to listen to the electrical signal of muscles. The signal is converted to a line tracing-very similar to one that you would see on a heart exam or EKG. Your therapist and doctor then read the pattern to determine which muscles may be showing more or less of a problem. This type of exam works the best on the elbow muscles, where it is sometimes difficult to tell in a regular office visit which muscle is pulling too strongly. The EMG can help to show this. Below are EMG line tracings of muscles near the elbow. The top three muscles, the biceps, brachialis and brachioradialis, are muscles that bend the elbow. In the bottom row is the triceps, which straightens the elbow. The high and low part of each line drawing shows you that the muscle is “on” or “off”. When the benders (flexors) have a high signal the straighteners (extensors) should have a low signal and vise versa.

On the LEFT is a person without neurological problems and on the RIGHT is a patient’s signal. Notice the high and low points in the LEFT normative EMG tracing. That shows a muscle being “on” and “off” when it should be. On the RIGHT is a patient whose elbow tends to bend in too much. You can see the signals in the top two flexors are staying high most of the time. The last bending muscle, the brachioradialis is on somewhat too much, but not as much as the top two. The surgeon can decide to address each muscle separately based on how it is firing. Below, the picture on the left is the EMG set up. The electrodes are placed on the muscles with stickers. We do not currently use electrodes with wire placement. On the right is a patient with the whole EMG set up on. Most kids find it fun and cool since the laboratory is so “high tech”! Most parents, guardians and adults can do simple EMG interpretation by the end of the EMG test!

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