Transcutaneous electrical nerve stimulation (TENS) is a technique that delivers mild electrical currents across the intact surface of the skin to reduce pain. TENS is used by practitioners throughout the world to manage painful conditions and TENS equipment can be purchased by the general public so that they can self-administer treatment. There are thousands of experimental and clinical research studies published on TENS and related techniques yet there is uncertainty about the best way to administer TENS in clinical practice. This is because currents used during TENS can be administered in a...