TENS at rates of 50 to 100 Hz produces analgesia that is not reversible by naloxone. Stimulation of large myelinated fibers presumably blocks nociceptive transmission at the level of the spinothalamic tract cell bodies.

TENS can produce neuromodulation by three routes: presynaptic inhibition of the spinal cord, direct inhibition on an excited, abnormally firing nerve, or restoration of afferent input.

TENS is helpful in the treatment of many painful conditions. A recent blinded and controlled trail of TENS and exercise showed a signification benefit only in the exercise group. However, double blinded, controlled trials of TENS have shown it to be of significant benefit in the treatment of rheumatoid arthritis and osteoarthritis.

Proponents of TENS recommend its use early in a pain treatment program. The patients who respond best to TENS typically have neurogenic or musculoskeletal pain, as opposed to psychogenic pain.

Best results are obtained in those who receive it early in their course. The patient should learn to apply the TENS electrodes over or near the area of pain with the dipole parallel to major nerve trunks.

Patients should understand that they have to determine by trial and error the optimal electrode placement and stimulus intensity, and the therapist or physician should encourage the patient to adjust the unit.

TENS variables that can be adjusted include amplitude, rate, pulse width, and location of electrodes. There is no current research to support the use of one mode of TENS over another such as conventional, burst, modulated, brief-intense, acupuncture-like, strength-duration.

Adverse reactions to TENS are infrequent; the most common is skin hypersensitivity. TENS should be avoided over the carotid sinus, in patients with demand-type pacemakers, and during pregnancy.