What Do Myotonic Discharges on an EMG Sound Like?

During an electromyography (EMG) test, myotonic discharges create a very distinct sound that neurologists often compare to a “dive bomber” airplane or a revving motorcycle engine ^[1][2]. This occurs because the EMG machine translates the electrical activity of your muscles into an audio signal you can hear in the exam room. When a muscle with myotonia tries to relax, it continues to fire off electrical signals that rise and fall in speed and volume, creating that characteristic revving or dropping pitch ^[1][2]. While hearing loud, erratic noises coming from your own body during a medical test can be startling, the sound itself is completely harmless.

How the EMG “Hears” Your Muscles

An electromyogram (EMG) is a diagnostic test that measures the electrical health of your muscles and the nerves that control them. During the needle portion of the exam, the doctor inserts a tiny, thin pin into a specific muscle. This needle acts like an electrical antenna.

Muscle cells communicate and move using electricity. The EMG machine captures these tiny electrical impulses and converts them into visual waves on a screen, as well as audible sounds through a speaker. This allows the neurologist to literally “listen” to how your muscles behave when they are resting and when they contract. While you might feel a pinch or mild cramping from the needle itself, the sound you hear is simply the machine translating these electrical signals.

The Anatomy of the “Dive Bomber” Sound

In a healthy muscle, the electrical signals fall completely silent as soon as you relax the muscle. However, in conditions like myotonic dystrophy, the muscle cells are hyperexcitable—meaning their outer membranes are unstable and prone to firing off signals even when they shouldn’t ^[3].

If you have myotonia, the muscle cells have a hard time stopping their electrical activity after a contraction, or sometimes even just from the minor irritation of the needle entering the muscle. Instead of going quiet, the muscle continues to fire repetitive electrical signals ^[1]. It is important to know that the needle temporarily irritating the muscle to cause this response is a normal part of the test and does not cause permanent muscle damage.

The “dive bomber” sound happens because of two simultaneous changes in these extra signals:

• Frequency (Pitch): The speed of the electrical firing speeds up and then slows down.
• Amplitude (Volume): The size of the electrical signals gets larger, then smaller.

Doctors call this rising and falling pattern “waxing and waning” ^[1][2]. Just like a motorcycle engine revving up and then winding down, or an airplane diving out of the sky, the pitch and volume of your muscle’s electrical activity peaks and fades out over a few seconds ^[2].

What This Sound Means for Your Diagnosis

Hearing this “dive bomber” sound is a key diagnostic clue for your neurologist. It is the hallmark electrodiagnostic sign of myotonia—the delayed relaxation of a muscle after you use it ^[2][4].

• Confirming the condition: While you might feel stiffness or notice that it’s hard to let go of a doorknob, the EMG sound provides objective, medical proof that the stiffness is caused by electrical myotonia rather than joint pain or a different muscle issue ^[4].
• Guiding the diagnosis: Myotonic discharges are most commonly associated with genetic conditions like myotonic dystrophy (both Type 1 and Type 2) and non-dystrophic myotonias ^[5][6]. However, they can occasionally be seen in other muscle conditions, such as toxic myopathies from certain medications or inflammatory disorders ^[7][4]. This is why hearing this sound likely led your care team to recommend genetic testing to confirm your specific diagnosis ^[8].

It is important to know that the volume or length of the “dive bomber” sounds on your EMG does not perfectly match how stiff your muscles feel in your daily life ^[2][9]. You can have significant myotonic sounds on an EMG but only experience mild stiffness, or vice versa ^[10].