Four out of five adults will experience at least one episode of back pain at some time in their lives, Statistics Canada says.

A portable device that uses electrical stimulation is not recommended to treat chronic low-back pain, a new guideline says.

Transcutaneous electric nerve stimulation or TENS uses a pocket-sized unit to apply a mild electrical current to the nerves through electrodes. It is used to relieve pain, strengthen muscles and enhance healing of soft tissue injuries, according to the American Academy of Orthopaedic Surgeons.

No one knows how TENS works to provide pain relief. It's thought that TENS stimulation may confuse the brain and block pain signals from getting through nerves.

The American Academy of Neurology released the guideline Wednesday in its online issue of the medical journal Neurology.

"The strongest evidence showed that there is no benefit for people using TENS for chronic low-back pain," said guideline author Dr. Richard Dubinsky of Kansas University Medical Center in Kansas City.

"Doctors should use clinical judgment regarding TENS use for chronic low-back pain. People who are currently using TENS for their low-back pain should discuss these findings with their doctors," he added in a release.

In drafting the guidelines, the authors reviewed evidence on the use of TENS for chronic low-back pain that has persisted for three months or longer. The chronic back pain studies reviewed excluded people with known causes of low-back pain, such as a pinched nerve or the curving of the spine known as severe scoliosis.

The authors concluded TENS can be effective in treating diabetic nerve pain, also called diabetic neuropathy, but more and better research is needed to compare it with other treatments for this type of pain.

Back pain — both acute and chronic — is the second commonest neurological ailment in the United States, according to the National Institute of Neurological Disorders and Stroke. It's estimated four out of five Canadians will experience back pain at some point in their lives, and it is a common reason for sick leaves.