The 422 is a Cordless Mini TENS Stimulator, TENS works by stimulating nerves close to the skin releasing endorphins (natures anaesthetics) and helping to block the pain signals sent to the brain. Relief can begin within minutes and a 30 minutes treatment can give up to 12 hours relief or more. The HomeClinic® mini TENS is totally cordless and has 12 different programmes for shoulder pain, back/neck pain, aching joints, rheumatic pain, migraines/headaches, sports injuries and period pain. In fact, overall body treatment. Each programme is fully adjustable for intensity and duration to suit your individual needs, simply set the programme on the easy to read digital display and gently press the self-adhesive pad to the area required.