Transcutaneous electrical nerve stimulation, more commonly referred to as TENS , is defined by the American Physical Therapy Association as application of electrical current through the skin for pain control . The unit is usually connected to the skin using two or more electrodes. A typical battery-operated TENS unit is able to modulate pulse width, frequency and intensity. Generally TENS is applied at high frequency (>50 Hz) with an intensity below motor contraction (sensory intensity) or low frequency (<10 Hz) with an intensity that produces motor contraction (Robinson and Snyder-Mackler, 2008).TENS is a non-invasive, safe method to reduce pain, both acute and chronic. While controversy exists as to its effectiveness in the treatment of chronic pain, a number of systematic reviews or meta-analyses have confirmed its effectiveness for postoperative pain, osteoarthritis, and chronic musculoskeletal pain .