The method of transcutaneous electric nerve stimulation

Transcutaneous electrical nerve stimulation (T.E.N.S) uses low-voltage electrical currents to relieve pain. A TENS unit is a small device that delivers the current at or near your nerves to block or change your perception of pain. Healthcare providers use TENS to treat a range of conditions, including osteoarthritis, tendinitis and fibromyalgia.

Transcutaneous electrical nerve stimulation (T.E.N.S) is a type of pain relief therapy. It uses a low-voltage electrical current to block pain or change your perception of it.

The method of T.E.N.S

T.E.N.S is a method of electrical stimulation which primarily aims to provide a degree of symptomatic pain relief by exciting sensory nerves and thereby stimulating either the pain gate mechanism and/or the opioid system. The different methods of applying T.E.N.S relate to these different physiological mechanisms. The effectiveness of T.E.N.S varies with the clinical pain being treated, but research would suggest that when used ‘well’ it provides significantly greater pain relief than a placebo intervention. There is an extensive research base for T.E.N.S in both the clinical and laboratory settings and whilst this summary does not provide a full review of the literature, the key papers are referenced. It is worth noting that the term T.E.N.S could represent the use of ANY electrical stimulation using skin surface electrodes which has the intention of stimulating nerves.

Mechanism of action

The stimulation delivered by the T.E.N.S unit aims to excite the sensory nerves, activating specific natural pain relief mechanisms. These mechanisms primarily include the Pain Gate Mechanism and the Endogenous Opioid System. Different stimulation parameters are used to activate these two systems and their effectiveness may vary based on individual responses.

Pain gate mechanism

The pain gate mechanism involves activation (excitation) of the A beta (Aβ) sensory fibres, which reduces the transmission of the noxious stimulus from the ‘C’ fibres, through the spinal cord to higher brain centres. This mechanism provides pain relief by essentially "closing the gate" to pain signals.

Frequency range

The Aβ fibres are optimally stimulated at a high frequency, typically 90 - 130 Hz (or pulses per second - pps).

Individual variability

There is a no single frequency that works best for every patient, but this range appears to cover the majority of individuals. Patients should adjust the settings to find their optimal treatment frequency for maximum effectiveness.

Endogenous Opioid System

The other pain relief mechanism involves stimulating the A delta (Aδ) fibres which respond better to lower frequencies. This stimulations activates opioid mechanisms, leading to the release of endogenous opiates (E.G., enkephalins, endorphins) in the spinal cord that inhibit the transmission of noxious sensory signals.

Impedance of current flow

The amount of electrical current flowing through body tissues is influenced by the impedance of the pathway - this is a measure of how readily the body allows the current to pass.. Impedance in biological tissues consists of resistive (ohmic) properties and reactive elements, which can be capacitive or inductive. The inductive elements are negligible in body tissues, meaning they do not significantly affect current flow.

Ohmic resistance refers to the resistance to direct current flow offered by tissues. Tissues that have a high water content, such as blood, muscle, and nerve, present less resistance, i.e., they have a lower ohmic resistance. Conversely, tissues such as bone and fat offer more resistance, and the skin's outer layer, the epidermis, has the highest resistance.

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