Chronic musculoskeletal pain is a major problem in society. Treatments for people with musculoskeletal pain have limited efficacy. Transcutaneous Electrical Nerve Stimulation (TENS) is a commonly utilized, non-invasive treatment for pain that is a safe non-pharmacological treatment that has been utilized for treatment of musculoskeletal pain. Recent studies in animals in the PIs laboratory have begun to examine the mechanism of action of TENS. The current study is proposed to translate the findings from the animals to human subjects. One concern with TENS is that there is not an appropriate placebo. Since TENS delivers an electrical current through the skin to produce pain relief, patients can typically feel the stimulation under the electrodes. The standard placebo in prior clinical studies has been to utilize a unit that appears to be functioning (lights on) but does not deliver a current. In this case the subject would not feel the stimulation. We will compare this standard placebo to a new device in which a current is delivered for 30 seconds and then slowly ramps to off. This current would then be felt by the subject as intensity is set, and then would slowly ramp down. Thus, electrical currents will be felt by the subject. It is common for people to adapt to the TENS current so that they no longer feel the stimulation over time, or that the stimulation is felt at a lower intensity. This new placebo TENS would appear to mimic this event to the subjects. This new TENS would have the further advantage of being able to double-blind the study so that the therapist applying the treatment, and the subject receiving the treatment are unaware who is receiving the active treatment. The investigators will therefore test the adequacy of this placebo when compared to a standard placebo with no stimulation.

Hypotheses:

1. TENS will reduce temporal summation and increase nociceptive threshold in normal subjects
2. Placebo TENS with a short burst of electrical stimulation will be considered by subjects to be an active TENS unit with a greater frequency than the standard TENS unit that does not produce electrical current
3. effectiveness of TENS will be associated with genotype of candidate pain genes (SNPs).