This question gets asked for two quite different reasons. Some people are anxious that they will somehow do the test wrong and be told nothing is the matter when something plainly is. Others are asking whether the result can be influenced.
Both deserve a straight answer, and the straight answer is the same: the part of the study that carries most of the diagnostic weight is not under your control. There is no way to perform well or badly at it.
A nerve conduction study is a measurement, not an examination
There is no score and nothing to pass. A small electrical pulse is delivered to a nerve at a known point, and the response is recorded further along. Three things are measured: how long the signal took, how large it was, and how fast it travelled.
None of those are volitional. You cannot decide to conduct more slowly, and you cannot will your amplitude down. The result is a property of the nerve.
This is why the phrase “failing” does not apply. An abnormal result is a finding, not a failure — and often the finding is the thing that finally explains a symptom nobody could account for.
The one part that needs your cooperation — and why effort does not fool it
The needle electromyogram has a segment where you are asked to contract a muscle. That part does depend on you, so it is worth being clear about what the examiner sees.
During the needle study the muscle is examined twice over: first at rest, then during contraction. As Jim Lewis R. NCS.T, CNCT describes the rest portion, the instruction is simply “relax, relax, relax” while the needle is moved through several depths and trajectories to sample the muscle properly.
What happens at rest is entirely involuntary. In a normal muscle the electrical activity settles and goes quiet. Where a nerve supply has been injured, the muscle produces fibrillations and positive waves — spontaneous electrical discharges that appear on their own. Lewis is explicit that these are the abnormal findings that matter, and that in practice they are identified as much by sound as by sight: “it's better to hear it than to see it.”
You cannot generate fibrillations by trying, and you cannot suppress them by trying. They are produced by an injured nerve-muscle connection or they are not.
The contraction portion is where deliberate under-effort would theoretically show — and it is also where it is most visible. The examiner is reading the recruitment pattern: how many motor units fire, and how fast. Genuine nerve injury produces reduced recruitment, where, in Lewis's description, “even though I'm contracting as full as I can, I'm not producing a lot of motor units” — few units firing very rapidly. Submaximal effort looks different: normal units, available in normal numbers, simply firing slowly. To someone who reads these daily the two are not easily confused.
And the contraction portion does not stand alone. It is interpreted alongside the resting findings, the nerve conduction numbers and the clinical examination, none of which move with effort.
What actually causes a misleading result
Invalid studies do happen. They are almost always technical, and the patient is rarely the cause.
Temperature is the first and largest. Cold nerves conduct slowly, which looks exactly like a demyelinating abnormality and is not one. Lewis calls it “the number one thing” and warms every patient to at least 32 degrees in the upper limb before recording. The detail people miss is that this is not a cold-climate problem — “if you're in Florida, believe it or not, even though it's warm outside, if they've been waiting in that waiting room for fifteen minutes, they've cooled down.” Skin can also read warmer than the nerve underneath it.
Too few nerves examined. An hour-long study compressed into twenty minutes is not a faster study, it is a smaller one. Lewis is blunt about seeing exactly that: “I see people doing these in twenty minutes all the time. Give yourself enough time.”
Inconsistent measurement. Distances are fixed by protocol precisely so results can be compared to normal values — the standard sensory distance is 14 centimetres. Measure differently and the numbers stop meaning what the reference range says they mean.
No usable comparison. Comparing the symptomatic side with the other side is powerful when a condition is one-sided. It fails when both sides are abnormal — Lewis notes that with an underlying diabetic peripheral neuropathy “the side-to-side comparison may not be quite as useful.” That is exactly the patient in whom a superimposed carpal tunnel is easiest to miss.
A normal study when you still have symptoms
This is the outcome people actually fear, and it has a real explanation that is not disbelief.
Nerve conduction studies assess large myelinated fibres. Small-fibre neuropathy affects nerves the test does not measure, so burning, tingling and temperature-related pain can coexist with a completely normal study. The study is also blind to structures it does not assess: it cannot see a disc, and it will not explain pain arising from a joint, tendon or muscle.
Timing matters as well. The needle study detects changes that take weeks to develop after a nerve is injured. Tested too early, the muscle has not yet had time to show them.
A normal result narrows the field. It does not say the symptom is imagined.
How to give the study its best chance
- Arrive warm and stay warm. Wear long sleeves, keep your coat on in the waiting room, and say so if your hands or feet are cold when you are called.
- Skip lotion or oil on the day — electrodes need clean skin contact.
- Bring your list of medications and conditions, particularly diabetes, thyroid disease, prior neck or back surgery and any previous nerve injury.
- Mention a pacemaker, implanted defibrillator or nerve stimulator before anything begins.
- Say if you take blood thinners — it may change the needle portion.
- Try to relax when asked to. Tension adds electrical noise that makes the recording harder to read, which is a real problem for the examiner even though it is not a way to fail.
- Contract as asked. Holding back does not protect you from an unwanted result; it makes the study harder to interpret and may mean repeating it.
The result has to fit the patient
The principle Lewis returns to throughout the course is whether a finding fits clinically — whether the physiology matches the history and the examination.
A study that contradicts a clear clinical picture is a reason to examine the study, not to overrule the patient. Check the temperature. Check the distances. Check which muscles were sampled. The most common cause of a surprising electrodiagnostic result is a technical one, which is the strongest reason of all not to think of this as a test you can pass or fail.
Learn blocks with your hands, not from a page
Empire’s Pain Management Training (THE Pain Show) is accredited for 25.25 AMA PRA Category 1 Credits™, jointly provided by AKH, Inc, and Empire Medical Training. For narrower peripheral work, Joint, Extremity and Non-Spinal Injection Training carries 6.75 credits for the complete in-person hybrid program, and Advanced Musculoskeletal Ultrasound Guided Injections builds the guidance skills above.
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