If it is working on the settings you are using then stick with those. TENS only works at the level of the skin as the penetration depth is not enought to directly affect muscle spasm. I would suggest that the sensory distraction from the skin sensors are resulting in a relaxing of the muscles around the painful area. Your TENS machine should have a manual in which there should be guidance. If you don't have it google it as most are able to be found on the web.