TENS (transcutaneous electrical nerve stimulation) refers to to the transmission of small electrical pulses through the skin to the underlying peripheral nerves. The basic principle behind conventional or high frequency TENS is that large nerve fibres can be selectively stimulated by adjusting the pulse amplitude, pulse width and repetition rate of specially selected wave forms. These large fibres have a lower threshold for stimulation and faster conduction velocity than the small fibres that conduct pain messages. Therefore if they are recruited they can create a gating mechanism that blocks small fibre activity and stops the pain signals from reaching the spinal cord, thus blocking pain. The nerve supplying the painful area is stimulated preferably by placing the two electrodes over it. When placed accurately, the TENS current will influence the segmentally related spinal cord systems implicated in the pain problem. Maximal pain relief occurs after 20 minutes.
Low frequency TENS (1-10 Hz, but optimally between 1 and 4 Hz) may cause the body to release its own pain relieving substances, called endorphins. At this rate it is necessary that visible low rate muscle contractions take place. This method of pain mediation is similar to that achieved through acupuncture.
If your pain is chronic you may be prescribed a TENS unit for home use by your family physician or physiotherapist. Your physiotherapist can assist you with optimal electrode placement and parameters for your condition.
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