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How Does an EMG Machine Work?

By Marco Sumayao
Updated Mar 03, 2024
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Electromyography (EMG) helps detect possible abnormalities in the human body by recording electrical impulses created by muscular activity for medical analysis. There are two general types of EMG machine: surface and intramuscular. Surface EMG detects activity through electrodes placed on the surface of the skin. An intramuscular EMG machine, on the other hand, detects activity through needles inserted directly into the muscle. The degree of invasiveness and resulting sensitivity of the two methods allow for different medical applications.

An EMG machine measures the size, frequency, and general shape of motor unit potentials generated by the patient's movement. When a motor neuron innervates muscle fibers, a slight electrical discharge is emitted from the neuron into the muscle fibers. An electromyograph can detect the sum of this activity and record it for interpretation. EMG tests record the activity both when the muscles are at rest and when the patient contracts them. In order to get accurate measurements, experts usually collect anywhere from 10 to 20 readings before ending the test.

A surface EMG machine works by placing electrodes onto the patient's skin, secured by adhesive patches. These electrodes are connected to fine wires that relay any electrical stimulation they receive from the body back to a device that can register and record the impulses. Technicians can then interpret the readings and identify any unusual activity.

An intramuscular EMG machine, on the other hand, is more invasive and involves the insertion of needle electrodes into the patient's skin. Readings can immediately be taken as the needle penetrates the skin and can provide valuable insight into the patient's muscle activity. Since the electrodes can measure motor unit potentials at a closer proximity, intramuscular EMG is usually much more accurate and in-depth than surface EMG. At times, the sensitivity of the measuring device can be deemed unnecessary for tests requiring simpler diagnoses.

Electromyography can help doctors determine whether or not patients have certain disorders, and if the causes are muscular or neurological in nature. Muscular disorders usually exhibit low-amplitude readings as a result of decreased muscle activity, while neurological disorders have typically higher amplitudes due to the re-firing of motor neurons. EMG tests are often recommended for patients experiencing tremors, loss of muscle control, or unusual muscle weakness in order to diagnose the causes of these abnormalities. Athletic trainers can also use an EMG machine to track the physical development of their clients and adjust their workouts according to the findings.

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