Electromyography (EMG)

What is an EMG?

Electromyography, or EMG for short, is a neurological test used to measure the electrical activity of a muscle. This shows whether a problem is located within the muscle itself or whether a supplying nerve is affected. EMG helps to distinguish between muscle and nerve disorders and is an important diagnostic tool for unclear weakness or paralysis.

What does an EMG examine?

An EMG checks whether and how well muscles process electrical signals. For example, it can detect nerve damage that may cause weakness or paralysis. Often, an EMG shows whether an injured nerve is starting to recover – long before a patient notices any improvement. The test is very sensitive and can reveal subtle changes that other methods may not detect.

Illustration of an EMG examination on a patient’s right forearm. — An EMG measures electrical activity directly inside the muscle – shown here on the right forearm.

How does the examination work?

An EMG can be performed in two ways:

1. Surface EMG: Small electrodes are placed on the skin above the muscle. This method is completely painless and is sufficient for certain questions.

2. Needle EMG: A very fine, sterile needle electrode is inserted directly into the muscle. It measures the activity of muscle fibers in an area of just a few millimeters around the tip. This makes it possible to detect even the smallest changes.

The doctor thoroughly disinfects the skin before inserting the single-use needle. The test is usually performed while you sit or lie down. You will be asked to first relax the muscle and then gently or firmly tense it. This shows how the muscle works at rest and under load. During the examination, you will usually hear a noticeable crackling or rustling sound from the speaker – these are the electrical signals of your muscle fibers made audible in real time.

Illustration of an EMG test showing the discharge of a single muscle fiber. — EMG visualizes the discharge of individual muscle fibers.

Depending on the question, the test may take just a few minutes or up to about an hour, depending on how many muscles need to be checked.

Hygiene

Only sterile needles are used for EMG. The skin is carefully disinfected beforehand to prevent infections.

EMG needles – what exactly is used?

The fine needles used in EMG are technically not ordinary injection needles. They are special concentric needle electrodes.

These contain a tiny internal electrode tip, electrically insulated inside a thin metal casing. The inner tip records the muscle’s electrical activity, while the outer casing acts as a reference electrode. This setup makes the measurement very precise and limits it to a very small area just a few millimeters around the needle tip.

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Thanks to this design, even the signals of single muscle fibers can be recorded without disturbing surrounding tissue. All EMG needles are sterile and used only once.

Blood thinners – what should you know?

If you are taking blood-thinning medication (such as warfarin, Eliquis®, Xarelto®, or aspirin), please inform your doctor before the examination.

In general, an EMG can usually be performed safely even while taking blood thinners, provided that the examination is medically necessary. During needle EMG, a very fine electrode is inserted into the muscle. This may rarely cause a small bruise, which is usually harmless and heals on its own.

Specialists recommend:

using muscles close to the surface, which can easily be compressed afterwards
carefully disinfecting the skin and applying gentle pressure after the examination

Experience and medical guidelines show that the risk of significant bleeding is very low.

Important: Please never stop taking your medication on your own. Always check with your doctor first if an adjustment is needed.

Is EMG combined with other tests?

Yes. EMG is often combined with a nerve conduction studies (NCS) to check how well a nerve conducts signals. In some cases, a muscle ultrasound is also useful to choose the exact area to examine and to guide the needle precisely. This increases both the safety and the accuracy of the test.

Illustration showing a nerve examined with ultrasound and nerve conduction study using electrodes and signal curves. — Modern nerve diagnostics combine high-resolution ultrasound with neurophysiological measurements such as EMG and nerve conduction studies.

Is EMG painful?

Most patients compare the prick of the fine needle to an acupuncture needle – a quick, barely noticeable sting. Most people tolerate the test well. Sometimes the muscle may feel a bit unusual or sore when tensed with the needle in place, similar to mild muscle ache. Afterwards, a small bruise can sometimes appear at the injection site, but this is usually harmless and fades quickly.

In summary

Electromyography is a safe and proven method for detecting nerve damage and muscle disorders and for monitoring recovery. It provides valuable information on whether an injured nerve is healing and what treatment makes sense. When performed carefully and hygienically, EMG is well tolerated by most patients and is an important tool for a precise diagnosis.