TENS (Transcutaneous Electrical Nerves Stimulation) is an electrotherapy used strictly for pain relief. It works by closing the body's "pain-gate mechanism" -- stopping the electrical pain signals from reaching the brain. TENS has been used for many decades with some success. It is effective about 65% of time on acute pain and helps approximately 50% of chronic pain sufferers.
Interferential Stimulation (IF) improves upon the basic premise of TENS by combining two moderate frequencies to induce a therapeutic low frequency in deep tissue. It works not only to block the body's pain signals but also increases blood flow to injured areas and stimulates injured muscles. IF can treat larger areas and those deeper in the body.