The two main types of e-stim are transcutaneous electrical nerve stimulation (TENS) and electrical muscle stimulation (EMS).
TENS may be used for chronic (long-term) pain as well as for acute (short-term) pain. Electrodes are placed on the skin near the source of the pain. Signals are sent through nerve fibers to block or at least reduce the pain signals traveling to the brain.
EMS uses a slightly stronger current than TENS to get muscles to contract. The unit’s electrodes (also placed on the skin near the affected muscles) cause rhythmic contractions. This can improve muscle strength if the user attempts to contract the muscle simultaneously.