TENS works by stimulating nerves close to the skin releasing endorphins which help block pain signals sent to the brain. Relief can begin within minutes, and a 30 minute treatment can give up to 12 hours relief. Ideal for shoulder pain, back/neck pain, aching joints, rheumatic pain and migraines/headaches. Three different modes of operation are available - burst, constant and modulation - and the pulse rate is variable. Supplied with case, battery, electrodes and instructions.