Electromyography (EMG)

Every time you move, your brain sends electrical signals through your nerves to your muscles. Electromyography (EMG) is a test that looks at how well your muscles and the nerves that control them are working. During an EMG test, providers measure electrical activity in muscles at rest and during movement. If you’re feeling numbness, weakness, or pain, this test helps identify problems with the muscles, the nerves, or how they communicate, especially when symptoms can’t be fully explained by other tests. 

Neurologists and physiatrists perform EMG testing and interpret the results. At Penn Medicine, care is delivered through a dedicated neurodiagnostics program, where an experienced team uses advanced testing to evaluate nerve and muscle function. This includes specialized techniques like single fiber EMG, along with coordinated care across neurology and rehabilitation services to support an accurate diagnosis and guide next steps.

There are a few ways to perform an electromyography test. Often, more than one method is used during your visit to better understand muscle and nerve function. Your care team will explain each step, answer questions, and adjust the pace to help you stay as comfortable as possible.

Needle-based EMG tests

Some EMG tests use a very thin needle to record electrical activity from muscles. These needles are single use and designed to minimize discomfort. You may feel a quick pinch, but most people tolerate the test well.

• Needle EMG: This test records electrical activity in muscles at rest and during movement to help identify muscle and nerve-related conditions, like carpal tunnel syndrome or pinched nerves.  
• Single-fiber EMG (SFEMG): This highly sensitive test records activity from individual muscle fibers to diagnose conditions that affect nerve-to-muscle communication, like myasthenia gravis. It’s often used when other tests are inconclusive.

Surfaced-based nerve and muscle tests

Some tests use sensors placed on the skin and don’t involve needles.

• Surface EMG (sEMG): This test measures muscle activity during movement to evaluate coordination, muscle function, and conditions like low back pain or muscle spasticity.
• Nerve conduction velocity study: This is a separate but related test that’s often done alongside an EMG. It uses small electrical pulses to measure how fast and strong signals travel through nerves, helping detect nerve damage or compression. It evaluates the nerve itself, while an EMG shows how muscles respond to those signals.

An EMG test usually takes about 30 to 90 minutes, depending on the type of test and how many muscles and nerves are being evaluated. 

If you’re having a nerve conduction study first, you’ll feel small taps from adhesive electrodes placed on your skin. For a surface EMG, electrodes are placed on the skin where you’re having symptoms. For a needle EMG, a very thin needle, about the size of an acupuncture needle, is inserted into the muscle. You might feel a mild pinch, but it usually doesn’t last long.

You’ll be asked to relax and then gently contract the muscle so the activity can be recorded. The machine shows this activity as wave patterns on a screen, and you may hear soft clicking sounds. Most people complete the test without difficulty. If you’re concerned about discomfort, you can take an over-the-counter pain reliever before you arrive.

Once the test is over, you can return to normal activities right away. You may feel some minor soreness or notice a small amount of bruising where the needles were placed, but this usually fades within a few days.

EMG results are typically available within one to two days. A specialist reviews the findings and shares them with the provider who ordered the test. Your care team will then meet with you to discuss the results and what they mean for your care.

At Penn Medicine, you have access to a full range of EMG testing, including specialized options like single-fiber EMG, which is available at only a few centers across Pennsylvania and New Jersey.

Testing is performed by experienced specialists who focus on nerve and muscle conditions every day. Our neurology team also works closely with researchers to advance diagnostic techniques, so you have access to the most up-to-date testing and care options.