Electromyography (EMG) and nerve conduction studies (NCS) are tests that measure muscle and nerve function. In most cases, both tests are performed. NCS is most often done first.

During NCS, mild electrical currents are applied to the skin on some parts of your body. This is done to see how quickly impulses travel between nerves. EMG assesses muscle function. To do this, a fine needle is placed under your skin into the muscle being tested. This is repeated on other muscles. The needle allows the electrical activity in your muscles to be measured. No electrical currents are applied with the needle.

During each test, wavy lines (waveforms) appear on a screen or on paper. These lines show how well your nerves and muscles work. These waveforms help to determine your test results.