Preparing for a Nerve Conduction Study and Electromyography

A nerve conduction study (NCS) and electromyography (EMG) are two electrodiagnostic tests typically performed together to evaluate nerve and muscle function. The combined visit usually lasts 30 to 90 minutes depending on how many nerves and muscles are tested. This page explains what the tests are, why they are ordered together, what to expect on the day of the appointment, and what the tests can and cannot tell you.

What these tests are

A nerve conduction study (NCS) measures how quickly and how strongly electrical signals travel through peripheral nerves. The test uses surface electrodes placed on the skin and delivers brief electrical stimuli to specific nerves, then records the responses. The three main parameters measured are conduction velocity, signal amplitude, and latency — how long the signal takes to reach the recording site. The American Association of Neuromuscular & Electrodiagnostic Medicine maintains patient information on NCS at aanem.org.

Electromyography (EMG) measures the electrical activity of muscles. A thin needle electrode is inserted into specific muscles, and the electrical signals produced — at rest and during voluntary contraction — are recorded. EMG provides information about motor nerve and muscle function and helps distinguish problems originating in nerves from problems originating in muscles. The AANEM also provides patient information on needle EMG at aanem.org.

Both tests are performed by a neurologist or physiatrist with electrodiagnostic training. The NCS portion is sometimes performed first by a trained technologist before the physician completes the EMG portion.

Why they are typically ordered together

NCS and EMG provide complementary information — NCS directly assesses nerve conduction; EMG assesses the functional consequences in muscle. Tankisi and colleagues published evidence-based recommendations for electrodiagnostic examination of polyneuropathy in a 2019 Clinical Neurophysiology Practice paper documenting how the combined study characterizes the type, location, and severity of nerve or muscle problems more accurately than either test alone (PMID 31886447).

For peripheral neuropathy, the combination identifies patterns consistent with length-dependent polyneuropathy, distinguishes demyelinating from axonal patterns, and identifies alternative diagnoses such as radiculopathy or focal nerve entrapment. For other neuromuscular conditions — muscular dystrophies, motor neuron disease, neuromuscular junction disorders, inflammatory myopathies — the combined study is the standard initial evaluation.

Day-of-test experience

Clothing. Wear loose-fitting clothes that allow access to arms and legs. Shorts and a short-sleeved shirt are ideal. Avoid jewelry on the limbs being tested.

Skin preparation. Do not apply lotion, moisturizer, oil, or powder to arms or legs on the day of the test. These products interfere with the adhesion of the surface electrodes used for NCS.

Eating and medications. No fasting is required. Take your usual medications unless specifically instructed otherwise. If you take blood thinners (warfarin, apixaban, rivaroxaban, dabigatran, clopidogrel, or others), inform the scheduling office in advance. Lynch and colleagues documented the hematoma risk with anticoagulants in a 2008 Muscle & Nerve paper — the EMG needle is small and complications are uncommon, but some clinicians prefer to assess the individual situation (PMID 18785182).

Body temperature. Cold limbs slow nerve conduction and can produce misleadingly abnormal results. The examiner typically warms the limbs before testing to ensure accurate measurements. Arriving warmly dressed in cold weather helps.

Implanted devices. If you have a cardiac pacemaker, implanted defibrillator, deep brain stimulator, or other implanted electronic device, inform the scheduling office and the physician in advance. NCS uses electrical stimulation that is generally safe with most implanted devices but specific protocols may apply.

What the sensations feel like

NCS sensation. Brief electrical stimuli are delivered through surface electrodes on the skin. Patients commonly describe the sensation as a small electrical zap, a tap, or a jolt lasting a fraction of a second. The intensity is adjusted to the minimum needed for a reliable signal. The sensation is uncomfortable but tolerable for most patients; some compare it to a static electricity shock.

EMG sensation. A thin solid needle electrode is inserted into specific muscles. The needle is solid — not hollow like an injection needle — and does not inject any substance. Patients commonly describe the insertion as a brief pinch similar to receiving a small injection. Once the needle is in place, you are asked to contract the muscle gently while electrical signals are recorded. Each muscle examined takes a few minutes. Preston and Shapiro's reference text Electromyography and Neuromuscular Disorders describes the standard approach in detail.

Most patients tolerate the test well. Discomfort during EMG is typically mild to moderate. If you have concerns about pain tolerance or anxiety, mention them at the time of scheduling and at the start of the appointment.

What happens after the test

Recovery is immediate. You can return to normal activities right away. Some patients notice brief muscle soreness at EMG needle sites for one to two days. Bruising is uncommon but possible, particularly for patients on blood thinners.

Results are typically interpreted by the examining physician shortly after the test, with a formal written report available within one to three business days. The report goes to the physician who ordered the test. The conversation about what results mean — and what they suggest about next steps — takes place at a follow-up appointment with the ordering physician, not at the NCS/EMG appointment itself.

Honest limitations of NCS and EMG

The tests measure only large myelinated nerve fibers. Small-fiber neuropathy — damage to the thin nerve fibers responsible for pain, temperature, and autonomic function — is not detected by NCS or EMG. England and colleagues confirmed this limitation in the American Academy of Neurology's 2009 practice parameter (PMID 19056666). A patient with small-fiber neuropathy can have severe and disabling symptoms and completely normal NCS/EMG results. A normal NCS/EMG does not rule out neuropathy; it rules out large-fiber neuropathy.

Limited sensitivity early in disease. In the earliest stages of some neuropathies, the tests may be normal because nerve damage is below the detection threshold. Repeat testing months later sometimes shows abnormalities not visible initially.

The tests do not identify causes. NCS and EMG describe patterns of nerve and muscle function but do not identify the underlying cause. Additional testing — laboratory tests, imaging, skin biopsy, or specialist consultation — is typically needed to characterize what is causing any abnormalities found.

When small-fiber neuropathy is suspected based on clinical features (burning, tingling, autonomic symptoms, normal large-fiber examination), skin punch biopsy with intraepidermal nerve fiber density measurement is typically the appropriate next step, as described in the Lauria and colleagues EFNS/PNS guideline (PMID 20642627).

What to bring

• A complete medication list, including blood thinners and any medications affecting nerve or muscle function
• Information about any implanted electronic devices
• Insurance card and any referral documentation
• A list of questions you want to ask the examining physician
• Loose, comfortable clothing allowing access to arms and legs

Frequently asked questions