Electrodiagnostic tests such as electromyography (EMG) and nerve conduction velocity studies are commonly ordered during the evaluation of patients with suspected peripheral nerve compression. Although these tests are invaluable extensions of the physical examination, many physicians are unable to interpret the test results, and so they base their operative decisions on electromyographers' impressions. A systematic approach to EMG interpretation allows surgeons to determine the nature and location of lesions as well as the degree of involvement and the viability of affected skeletal muscles.