The most common TENS programs use high-frequency stimulation, which is the first choice for both acute and chronic pain. High-frequency stimulation sends impulses to the nervous system’s own pain-inhibiting mechanisms, which block the pain. You can use it as often and as long as you like, but each treatment should last at least 45 minutes.
Another type of TENS is low-frequency stimulation. Low-frequency TENS treatment can alleviate pain by stimulating muscles to release the body’s own morphine-like substances, endorphins. Place the electrodes on a muscle in the painful area so that a visible contraction occurs. You can use low-frequency TENS for 20–45 minutes, three times a day. Low-frequency stimulation can lead to sore muscles.