Overcoming Analgesic Tolerance to TENS (OCTTT)

Healthy adults will come daily for 5 consecutive days to the testing room. Pressure pain thresholds (PPT) will be the outcome measure and will be used to measure the subject's pain threshold to deep mechanical pressure. Subjects will push a button to stop the PPT test when they first begin to feel a sensation of pain. The PPT test will be done before TENS application. The TENS unit will be applied based on random assignment to 1 of 5 treatment types and subjects will not be told which group they are assigned to. Those groups are: 1) placebo TENS, 2) high frequency TENS, 3) alternating frequency TENS, 4) modulated frequency TENS, or 5) high frequency TENS with increased intensity daily. The TENS unit will be applied for 30 minutes. After 20 minutes the PPT test will be completed a second time. This procedure will occur on all 5 consecutive days of testing. Data will be measured and recorded by an assessor blind to subject group. Blinding will be assessed at the end of testing on day 5.