Different Theories on How it Works
Electrical and chemical changes occur in the body as a result of injury and disease. Pain is the sensation we feel as the brain responds to these changes. These are communicated to the brain via the spinal cord as a result of input from sensory receptors at nerve endings at the source of the problem. Pain serves as a message to avoid a situation, to rest and to heal.

TENS is believed to work in two ways. One is through what is called “The Pain Gate Control Theory” or “gating effect.” By stimulating a nerve that is carrying the pain signal with the TENS unit, the pain transmission is blocked. Applying the current overrides the transmission of pain signals to the brain by inhibiting their transmission at the level of the spinal cord. This pain gateway is normally closed, and when pain is perceived from the peripheral nerves to the spine, it opens, allowing this information to be carried to the brain where we interpret it as pain. The opening of this gateway seems to be inhibited by TENS stimulation. The actual cause of the pain is not affected.

The second theory is that the electrical stimulation causes the body to release natural pain killers called endorphins due to the increase in brain activity. Endorphins have a strong effect on pain management and can be stronger than non-opiate pain medications. They flow through the circulatory system acting like a pain medication, and have an analgesic effect. These endorphins are released slowly but remain active for a period of 8-36 hours. Encephalins are also released, and these help more quickly with pain management, but remain active for a short period of time. High pulse TENS units are believed to stimulate release of encephalins while low pulse rate is used for endorphin release.

Repeated use of the TENS unit can result in a lessening of pain perception over time. Although the mechanism that causes this is not well understood, it is believed that if the pain messages are switched off enough, the state of reduced pain becomes the norm. If TENS is used prior to the return of the pain, the perception of reduced pain is sustained. This feeling is sent to the brain through nerves in the spinal cord’s dorsal column. In effect, the body has been reprogrammed to not feel the pain.

Conditions it Works Best For
The most common uses of TENS are for the reduction of pain and the improvement of muscular skeletal functioning. If used correctly and for a sufficient duration, studies have shown this modality to be effective for the relief of chronic pain, such as the pain caused by peripheral nerve damage and degenerative and mechanical muscular skeletal disorders. It has also been used for acute pain relief, such as post-operative pain and acute low back pain, and in situations where medication is contraindicated, such as labor pain. TENS has been extensively studied and proven effective in neuromuscular rehabilitation, i.e. muscle strengthening, increasing muscular endurance, motor re-education, and increasing range of motion. Studies have supported its effectiveness for short-term relief from osteoarthritic pain, but results are not as clear for the pain from rheumatoid arthritis. TENS also appears to be effective for the treatment of soft tissue inflammatory disorders, such as sprains, fractures and contusions.

Content last modified on Sep 4, 2003