Understanding Your EMG Results (2024)

Your doctor may recommend an EMG (electromyogram) to diagnose the cause of symptoms, such as muscle weakness and nerve problems. An EMG is a nerve conduction study that evaluates a muscle’s response to the nerve that controls it. It does this by measuring the electrical activity in the muscle at rest, with a slight contraction, and with a forceful contraction. This helps your doctor know whether the problem is in the muscle itself or in the nerves that control the muscle.

Keep in mind that an EMG is one tool in making a diagnosis. A doctor who specializes in neurology or physical medicine will interpret the results in the context of other tests and clinical information. The test can only reveal what is happening in the muscle; it can’t explain why it’s happening. That requires the expertise of your doctor.

Normally, a muscle at rest will not show any electrical activity on an EMG recording. When it contracts, it will show electrical activity as a wave line or action potential. The size and shape of the action potential gives your doctor information about the muscle’s ability to respond to the nerve that controls it. A normal muscle shows a smooth action potential in a normal EMG.

Abnormal EMG results can show up in two ways. First, the muscle may show electrical activity at rest. On the other hand, the muscle may show abnormal electrical activity during contraction. This shows up as an abnormal action potential pattern with changes in the size or shape of the wave. Abnormal EMG results may indicate muscle damage or a problem with the nerves that control the muscle.

There are five general categories of information about muscle activity that your doctor can get from an EMG:

1. Activity: Is the muscle turning on and off normally? Normal muscles turn on when necessary and turn off when they don’t need to act. An EMG test will record electrical activity when the muscle turns on. If an EMG shows constant muscle activity, it may indicate a problem, such as muscle spasticity.

2. Timing: Is the muscle firing at the right time? An EMG also measures when a muscle is active. Your doctor will look at the timing of muscle activity during a movement or in comparison to other muscles. This gives your doctor information about the pattern of muscle activity and whether it is normal or not.

3. Level: Is the muscle as active as a healthy muscle? An EMG test looks at how much activity the muscle has. In other words, the level of work or effort the muscle must make during a movement.

4. Comparison: Is the muscle more or less active in a comparison? The comparison may be between the two sides of the body, under different conditions, or some other situation.

5. Fatigue: Does the muscle tire easily? This last category is to evaluate muscle fatigue. This helps your doctor identify weak muscles. It can be useful in diagnosing the cause of conditions, such as low back pain. It also helps your doctor determine whether strengthening exercises are working.

An abnormal EMG result means there is a problem in an area of muscle activity—turning on and off, when it is active, how much it is active, if it is more or less active, and fatigue. This can offer a clue in diagnosing various nerve and muscle conditions. Learn more in 10 Conditions Diagnosed With an EMG.

EMG testing is one part of making a diagnosis. The results may not pinpoint a precise diagnosis, but it can narrow the possibilities.

Second opinions can be a valuable tool when trying to establish a neuromuscular diagnosis. Some medical centers even offer remote second opinions from experts in the field. Remember that a second opinion on your test results is not a negative reflection on your doctor. It offers additional input and reassurance about your situation.