Apparatus and method for diagnosing a source of muscular pain, wherein the apparatus includes a housing, an electrical signal generator mounted within the housing, and a pair of electrodes, one of which is mounted on one end of the housing and the other of which is mounted on an opposite end of the housing. The generator may include either an analog waveform generator or a digital signal processor. Each of the electrodes stimulates a muscle with an electrical signal generated by the generator. One of the electrodes has a relatively small contact area for targeting smaller muscles or muscle groups, while the other electrode has a relatively large contact area for targeting larger muscles or muscle groups. The apparatus is a self-contained, wireless unit and is highly maneuverable, which allows a user to quickly and easily diagnose a source of muscle pain.