Transcutaneous Electrical Nerve Stimulation (TENS)

Transcutaneous Electrical Nerve Stimulation (TENS) is an electrotherapy method used to treat pain by delivering specific low-frequency pulsed electrical currents into the body through the skin (targeting large-diameter peripheral nerve fibers). Emerging in the 1970s, TENS has proven effective for pain relief and is now widely used in clinical practice, particularly in the United States. Unlike traditional electrical stimulation, which primarily targets motor fibers, TENS is specifically designed to stimulate sensory fibers.

A TENS device must meet the following criteria:

1. Relatively high frequency: Typically ranging from 2 to 160 Hz, which falls within the low-frequency spectrum.

2. Short pulse duration: Generally between 9 and 350 μs. If the pulse duration is too long, it may activate pain-transmitting fibers and increase ionization under the electrodes. However, a longer pulse duration may be appropriate for individuals with a greater amount of adipose (fatty) tissue.

3. Appropriate intensity: The intensity should be set at a sub-threshold level—comfortable for the patient and insufficient to trigger muscle contractions. This allows TENS to selectively stimulate sensory (afferent) nerve fibers without activating motor (efferent) nerve fibers.

4. Varied current waveforms: Common waveforms currently in use include: (1) symmetrical biphasic square waves; (2) medium- or high-frequency currents modulated by unidirectional square waves; (3) symmetrical biphasic pulses; (4) unidirectional square waves; and (5) asymmetrical biphasic pulses.

(II) Contraindications

1. Patients with cardiac pacemakers: Particular caution is required for those with demand-type pacemakers, as TENS currents can easily interfere with the pacemaker's pacing rhythm.

2. Application over the carotid sinus.

3. Application to the lower back or lower abdomen in women during early pregnancy.

4. Patients with localized sensory loss or hypersensitivity to electrical stimulation.