PHYSIOTHERAPISTS USING TENS MACHINE: IS IT SAFE AND EFFECTIVE?

31. May 2021

physiotherapists using tens machine: is it safe and effective?

In modern physiotherapy, managing pain effectively is a cornerstone of successful rehabilitation, and one of the key tools used for this purpose is the TENS machine. The acronym TENS stands for Transcutaneous Electrical Nerve Stimulation, a term that precisely describes its function.¹ ‘Transcutaneous’ simply means ‘through the skin’, indicating that the therapy is delivered non-invasively.⁴ TENS is a well-established modality within the broader field of electro therapy, which uses electrical energy for therapeutic benefit.⁵

The treatment involves a small, portable, battery-operated device connected by wires to adhesive electrode pads. These pads are placed on the skin over or near a painful area, where they deliver mild, low-voltage electrical impulses to the underlying nerves.¹ The primary goal of this stimulation is to provide temporary, symptomatic pain relief for a wide array of both short-term (acute) and long-term (chronic) conditions.¹

It is crucial, however, to position TENS correctly within a modern healthcare context. It is not a standalone cure but rather an adjunctive therapy—a valuable component of a comprehensive physiotherapy treatment plan. The pain relief it provides is often a means to an end. By reducing the intensity of pain signals, TENS can empower individuals to engage more effectively with the active components of their rehabilitation, such as therapeutic exercise and manual therapy.⁵ In this capacity, TENS acts as an enabler, breaking the debilitating cycle of pain and inactivity and paving the way for treatments that address the root cause of the issue and promote lasting recovery.

What is a TENS machine and how does it work?

Understanding how a TENS machine functions requires looking at both its physical components and the sophisticated neurophysiological mechanisms it triggers within the body. This knowledge helps to demystify the treatment and explains why it can be an effective tool in a physiotherapist's arsenal.

The Device and Its Operation

A standard TENS unit consists of three main parts: a compact, battery-powered control box, one or more lead wires, and two or four self-adhesive electrode pads.⁹ The control unit is the "brain" of the device, allowing the user to precisely adjust several parameters of the electrical current:

Intensity (Amplitude): This controls the strength of the electrical impulse, typically measured in milliamps (mA). The user turns a dial or presses a button to increase the intensity until a strong but comfortable sensation is felt under the pads.⁷
Frequency (Pulse Rate): This determines how many electrical pulses are delivered per second, measured in Hertz (Hz). Different frequencies target different pain-relief mechanisms in the body.³
Pulse Width (Duration): This adjusts the length of each individual electrical pulse, measured in microseconds (µs). Wider pulse widths can create a sensation of deeper stimulation.³

When in use, the device generates a sensation often described as a pleasant tingling, buzzing, or prickling under the electrodes; it should never be painful.⁹ One of the key practical benefits of a TENS machine is its portability. The small control unit can be easily clipped onto a belt or tucked into a pocket, allowing individuals to remain mobile and continue with many of their daily activities while receiving treatment.⁴

The Scientific Mechanisms of Pain Relief

The ability of TENS to alleviate pain is not arbitrary; it is grounded in well-established theories of how the nervous system processes and perceives pain. Physiotherapists leverage these mechanisms by adjusting the machine's settings to achieve the desired therapeutic effect.

High-Frequency Stimulation and The 'Pain Gate' Theory

The most widely accepted mechanism, particularly for high-frequency TENS, is the Gate Control Theory of Pain, first proposed by scientists Ronald Melzack and Patrick Wall in 1965.¹⁴ This theory posits that there is a neurological "gate" mechanism within the dorsal horn of the spinal cord that can either block pain signals or allow them to proceed to the brain.

Our nervous system contains different types of nerve fibres that transmit information. Pain signals are typically carried by small-diameter, slow-conducting nerve fibres (A-delta and C-fibres). In contrast, non-painful sensations like touch, pressure, and vibration are carried by large-diameter, fast-conducting nerve fibres (A-beta fibres).¹⁴

When a TENS machine is set to a high frequency (typically between 80-130 Hz), it selectively stimulates these large, fast A-beta fibres.⁴ The signals from these stimulated fibres travel to the spinal cord much more quickly than the pain signals from the smaller fibres. This high volume of non-painful sensory information effectively overwhelms the neurological gate, "closing" it to the ascending pain signals.³ In essence, the brain becomes preoccupied with processing the tingling sensation from the TENS unit, so fewer pain messages get through. This is the same principle that explains why instinctively rubbing a bumped elbow can make it feel better; the physical sensation of rubbing helps to block the pain.⁴

Low-Frequency Stimulation and The Endogenous Opioid System

A second, distinct mechanism is activated when the TENS machine is set to a low frequency, often referred to as acupuncture-like TENS (AL-TENS), typically between 2-5 Hz.⁴ This type of stimulation is designed to trigger the body's own pain-relief system.

The low-frequency pulses encourage the brain and spinal cord to release natural pain-killing chemicals called endorphins and enkephalins.¹ These substances are endogenous opioids, meaning they are produced within the body but function in a similar way to opioid medications like morphine.⁴ They bind to opioid receptors in the central nervous system, blocking the perception of pain and promoting a sense of well-being.⁸

Unlike the immediate effect of the pain gate mechanism, the relief from endorphin release may have a slightly slower onset but can often last for several hours even after the TENS machine has been turned off, due to the longer-lasting action of these chemicals in the nervous system.¹⁴

Advanced Mechanisms: Descending Inhibition

To provide a more complete picture, it is also understood that TENS can activate complex descending inhibitory pathways.¹⁴ This means that the stimulation not only blocks pain signals at the spinal cord level but also sends signals up to higher centres in the brainstem, such as the periaqueductal gray (PAG) and rostral ventromedial medulla (RVM).¹⁷ These brain regions, in turn, send signals back down the spinal cord to inhibit the transmission of incoming pain signals at their source. This adds another powerful layer of centrally mediated pain modulation, demonstrating that TENS interacts with the nervous system in a multifaceted way.

To clarify how these mechanisms translate into practical application, the different modes of TENS used in physiotherapy are summarised below.

Mode Name	Typical Frequency	Primary Mechanism	Sensation Felt	Common Use in Physiotherapy
Conventional TENS	High (80−130 Hz)	Gate Control Theory	Strong, non-painful tingling or buzzing	Acute pain management (e.g., post-injury, post-operative) for immediate, short-term relief.
Acupuncture-Like TENS (AL-TENS)	Low (2−5 Hz)	Endogenous Opioid Release	Rhythmic, visible muscle twitching or pulsing	Chronic pain conditions where longer-lasting relief is desired.
Burst Mode TENS	High-frequency pulses delivered in low-frequency bursts	Both Gate Control & Opioid Release	A pulsing or "grabbing" tingling sensation	Chronic pain; may be effective for individuals who adapt (accommodate) quickly to other modes.

What can a TENS machine be used for?

As a versatile and patient-controlled modality, TENS is a physiotherapy treatment utilised for a broad spectrum of both acute and chronic pain conditions across various patient populations in the UK.² Its application is guided by the nature of the pain and the specific goals of the patient's rehabilitation plan. Below are several key areas where TENS has demonstrated a positive effect.

Positive Effects on Arthritis Pain

For the millions in the UK living with arthritis, managing chronic joint pain is a daily challenge. TENS is recommended by the NHS as a non-pharmacological treatment option for both osteoarthritis and rheumatoid arthritis.¹⁹

Osteoarthritis (OA): This "wear and tear" form of arthritis often affects weight-bearing joints like the knees and hips. TENS can help by applying a small electrical pulse to the affected joint, which numbs the nerve endings and helps to ease the persistent ache and stiffness.¹⁹ Evidence suggests that for knee OA, TENS can reduce pain intensity more effectively than a placebo treatment.²¹ A 2015 Cochrane Review found tentative evidence for its benefit, and it is estimated that approximately half of the people who try TENS for OA experience a 50% reduction in their pain.²¹
Rheumatoid Arthritis (RA): In this autoimmune condition, TENS can be used as an adjunctive therapy to help manage the pain associated with joint inflammation.¹³ By providing symptomatic relief, it can improve a patient's ability to perform daily activities and participate in gentle exercises designed to maintain joint mobility and muscle strength.

A significant advantage for individuals with chronic conditions like arthritis is that effective TENS use may help reduce their reliance on long-term pain medications, thereby minimising potential side effects associated with those drugs.¹⁸

Positive Effects on Lower Back Pain

Lower back pain is one of the most common musculoskeletal complaints, affecting people of all ages. TENS is frequently recommended as a useful self-help tool for providing short-term relief from both acute episodes (e.g., after a muscle strain) and chronic, persistent back pain.²² Its mechanism in this context is twofold: the electrical impulses distract the nerves from transmitting pain signals, while also helping to relax the painful muscle spasms that often accompany back injuries.²²

However, the true value of TENS in the physiotherapy management of back pain extends beyond simple pain relief. Many individuals with back pain fall into a vicious cycle: pain leads to fear of movement, which leads to inactivity. This deconditioning, in turn, can worsen the underlying problem and perpetuate the pain. TENS can act as a powerful functional enabler by breaking this cycle. By providing a temporary window of significant pain reduction, it gives patients the confidence to move and participate in the crucial, evidence-based exercises that form the core of modern back pain rehabilitation.²³ It is not merely about feeling better while resting; it is about feeling well enough to perform the therapeutic activities prescribed by a physiotherapist that are essential for building core strength, improving flexibility, and achieving long-term recovery.²²

Positive Effects in Post-Operative Pain Management

Following surgery, effective pain control is paramount for patient comfort and a successful recovery. TENS has emerged as a valuable, non-pharmacological component of multimodal analgesia, particularly after orthopaedic procedures such as total knee replacement (TKA) and spinal surgery.²⁵

Numerous studies and meta-analyses have shown that using TENS in the immediate post-operative period (the first 24-48 hours) can significantly reduce pain scores, especially pain experienced during movement.²⁷ Perhaps more importantly, its use has been consistently linked to a reduction in the consumption of potent opioid analgesics like morphine.²⁹ A 2003 meta-analysis found that when TENS was administered with adequate intensity, it reduced analgesic consumption by an average of 35.5% compared to placebo.²⁹

This is clinically significant because reducing opioid use can lead to fewer unpleasant side effects, such as nausea, dizziness, and sedation.²⁷ By mitigating these effects, TENS facilitates earlier and more comfortable mobilisation. Getting patients up and moving sooner after surgery is critical for preventing complications like deep vein thrombosis and chest infections, and for accelerating the overall recovery process. For TKA patients specifically, research has shown that TENS can lead to a significant improvement in the active range of knee motion, a primary goal of early post-operative physiotherapy.²⁸

Other Conditions with Positive Effects

The versatility of TENS allows it to be applied in a wide variety of other clinical situations. Chartered physiotherapists in the UK may incorporate it into treatment plans for:

Sports Injuries: For acute pain from muscle strains or ligament sprains.¹
Nerve Pain (Neuropathic Pain): To manage symptoms of conditions like diabetic peripheral neuropathy, pain related to multiple sclerosis, and phantom limb pain after amputation.¹²
Chronic Widespread Pain: For conditions such as fibromyalgia, where it can help manage pain during movement.¹⁸
Pelvic Pain: For chronic pelvic pain and pain associated with conditions like endometriosis or painful periods (dysmenorrhoea).¹
Cancer-Related Pain: Research supported by Cancer Research UK found that TENS could be useful for controlling pain caused by bone metastases, showing a particular benefit for pain experienced during movement.³²

Do TENS machines really work?

physiotherapist and patient with TENs machine The question of whether TENS machines are genuinely effective is a critical one for anyone considering this form of treatment. The answer is nuanced, as the scientific literature and clinical guidelines have presented a mixed picture over the years.¹⁷ However, a clearer consensus is emerging, pointing towards efficacy when the treatment is applied correctly and for the right purposes.

The Weight of Modern Evidence

For a long time, the debate around TENS was fuelled by numerous small, often methodologically flawed studies, leading to inconclusive results in many systematic reviews.¹⁷ This uncertainty has been significantly clarified by more recent, large-scale analyses.

A landmark systematic review and meta-analysis published in the BMJ Open in 2022, known as the "meta-TENS study," provided a powerful update. This comprehensive review synthesised the results of 381 randomised controlled trials involving a total of 24,532 participants.³⁴ Its primary conclusion was that there is moderate-certainty evidence that TENS, when administered at a strong but comfortable intensity, produces clinically important reductions in pain intensity during or immediately after treatment compared to a placebo. Crucially, this benefit was achieved without reports of serious adverse events.³⁴ This large-scale analysis provides a strong, evidence-based foundation for the use of TENS as an effective tool for short-term pain relief.

Understanding the Historical Controversy

Despite this strong evidence, patients may still encounter conflicting information, particularly regarding guidelines from bodies like the UK's National Institute for Health and Care Excellence (NICE). For instance, NICE has recommended against the use of TENS for chronic primary pain and non-specific low back pain, yet continues to recommend it as an adjunct therapy for osteoarthritis and rheumatoid arthritis.³⁴

This apparent contradiction can be understood by examining the quality of the underlying research. The effectiveness of TENS is highly dependent on the "dose" delivered, with stimulation intensity being a critical factor for success.¹⁶ For TENS to activate the pain-gating and opioid mechanisms effectively, the sensation needs to be strong and definite, not barely perceptible.¹⁴ Many older studies that found no benefit failed to ensure or even report an adequate stimulation intensity. Systematic reviews that specifically filter for trials using appropriate, strong intensities have consistently found significant positive effects, whereas those that include inadequately dosed trials often yield inconclusive results.¹⁶ Therefore, much of the historical uncertainty does not necessarily prove TENS is ineffective, but rather highlights that it is ineffective when used incorrectly. This transforms a point of confusion into a compelling argument for seeking professional guidance to ensure the therapy is administered properly.

The Crucial Role of the Physiotherapist in Ensuring Efficacy

This is where the expertise of a chartered physiotherapist becomes indispensable. Simply purchasing a TENS machine is not a guarantee of success. A physiotherapist plays a vital role in maximising the potential for pain relief by ³⁵:

Accurate Pad Placement: Showing the patient precisely where to place the electrode pads to target the nerves supplying the painful area.⁹
Optimising Settings: Teaching the patient how to adjust the frequency, pulse width, and intensity to find the optimal settings for their specific pain type and personal comfort level.¹²
Navigating the Learning Phase: Guiding the patient through an initial learning period, helping them to personalise their use of the device and develop strategies for different situations (e.g., using it at rest versus during activity) to achieve the best possible outcome.³⁶

Contextualising TENS within a Broader Physiotherapy Framework

It is also important to understand where TENS fits among other therapeutic modalities. TENS is a form of electro therapy focused on neuromodulation—changing how the nervous system perceives pain. This contrasts with other advanced treatments like shockwave therapy.

Shockwave therapy does not use electricity; instead, it uses high-energy acoustic (sound) waves to create a biological response within injured tissue.³⁸ This process, known as mechanotransduction, stimulates blood flow, enhances cellular metabolism, and promotes the release of growth factors, actively kick-starting the body's natural healing and regeneration processes.⁴⁰ It is often used for chronic tendon issues (like tennis elbow or plantar fasciitis) and aims to repair the underlying cause of the pain.³⁹

In short, TENS primarily provides symptomatic pain relief by masking the pain signal, while shockwave therapy is a regenerative treatment aimed at healing the source of the pain. A physiotherapist is expertly placed to diagnose the condition and determine whether a pain-modulating approach like TENS, a regenerative approach like shockwave therapy, or a combination of treatments is most appropriate for the patient's specific injury and stage of recovery.³⁸

Are there any side effects of using a TENS machine?

One of the most significant advantages of TENS as a pain management tool is its excellent safety profile. When used correctly and according to professional guidance, it is generally considered a very safe physiotherapy treatment with minimal risks or side effects, making it a popular drug-free alternative to pharmacological pain relief.¹⁰

Common and Minor Side Effects

The most frequently reported side effect is minor skin irritation under the electrode pads.⁷ This can manifest as redness, itching, or a rash and is often related to the adhesive on the pads or the build-up of moisture. This is typically mild and can be managed with simple, practical steps ¹:

Ensure the skin is clean and completely dry before applying the pads.
Slightly alter the position of the pads each time the machine is used to give the skin a rest.⁹
Remove the pads after each session to allow the skin to breathe.
If irritation persists, a physiotherapist can recommend alternative, hypoallergenic electrode pads.¹

Some individuals may find the tingling or buzzing sensation produced by the machine unusual or uncomfortable at first, but it should never be painful.¹¹ If the sensation becomes unpleasant or causes muscle contractions that are too strong, the intensity should be immediately reduced to a comfortable level.¹

TENS Safety Checklist: Contraindications and Precautions

While TENS is safe for most people, there are specific situations where it should not be used (contraindications) or where it should be used with caution (precautions). This is why a consultation with a GP or physiotherapist is essential before starting treatment. The following checklist, based on guidance from UK health authorities like the NHS, summarises the most important safety rules.¹

Category	Safety Guideline
DO NOT USE TENS IF (Absolute Contraindications)	You have a cardiac pacemaker, an implantable cardioverter-defibrillator (ICD), or any other type of implanted electrical device.¹	You have epilepsy, unless its use has been specifically approved by your doctor.¹	You are in the first trimester of pregnancy.⁹	The cause of your pain has not been diagnosed by a healthcare professional.¹
DO NOT Place Pads ON (Precautions - Placement)	The front or sides of your neck, near the carotid sinus.¹	Your temples, mouth, or directly over your eyes.⁹	Your chest and upper back at the same time.¹	Skin that is broken, infected, irritated, or has lost normal sensation (numbness).¹	Varicose veins or areas of thrombophlebitis.¹¹	Directly over the spinal column.⁹
DO NOT USE TENS WHILE (Precautions - Activity)	Driving a vehicle or operating heavy machinery.¹	Bathing or showering.¹	Sleeping.¹

Adhering to these guidelines is crucial for ensuring a safe and positive experience with TENS therapy.

Conclusion

Transcutaneous Electrical Nerve Stimulation (TENS) is a well-established, scientifically-backed modality that holds a valuable place in modern pain management. It is a safe, non-invasive, and effective tool for providing temporary relief from a wide variety of acute and chronic pain conditions when used as an integral part of a comprehensive physiotherapy treatment plan. Through mechanisms like the Gate Control Theory and the release of endogenous opioids, TENS can significantly reduce a patient's perception of pain, offering a much-needed alternative or complement to medication.

The true strength of TENS within a rehabilitation setting often lies in its role as an enabler. By modulating pain, it can break the debilitating cycle of discomfort and inactivity, empowering individuals to engage more fully with the essential active therapies—such as targeted exercise and manual techniques—that are fundamental to achieving lasting recovery and improved function. While the scientific evidence has been debated historically, recent large-scale analyses confirm its efficacy, particularly when the correct parameters are applied under professional supervision.

Given the importance of correct application and the need to rule out any contraindications, it is strongly recommended that anyone considering TENS should first consult with a qualified healthcare professional. A GP or a chartered physiotherapist can provide an accurate diagnosis, confirm that TENS is a safe and appropriate option for their specific condition, and offer personalised instruction on how to use the device for maximum benefit. Ultimately, when guided by professional expertise, a TENS machine can be an invaluable, patient-controlled component in a modern, evidence-based approach to physiotherapy.

Frequently Asked Questions about TENS Machines

Q: How much do TENS machines cost in the UK?

Most consumer TENS units range from £20-£100, with professional-grade devices costing more. Higher-priced models typically offer more programmable settings and better durability.

Q: Does the NHS provide TENS machines?

The NHS may loan TENS machines for short periods (particularly for labour pain), but generally patients need to purchase their own devices for long-term use. Your physiotherapist can advise whether you might qualify for an NHS-loaned device.

Q: How long should I use a TENS machine in one session?

Most physiotherapists recommend TENS sessions of 20-30 minutes, though this can be extended to 1 hour for chronic pain conditions. Always follow the specific guidance provided by your healthcare professional.

Q: How frequently can I safely use a TENS machine?

TENS can typically be used 3-4 times daily with rest periods between sessions. Overuse may lead to accommodation (reduced effectiveness) or skin irritation.

Q: Do I need a prescription to buy a TENS machine in the UK?

No, TENS machines are available without prescription from pharmacies, medical supply stores, and online retailers. However, consulting with a healthcare professional before purchase is strongly recommended.

Q: How do I clean and maintain my TENS machine?

Wipe the unit with a slightly damp cloth (never submerge in water), and store in a cool, dry place. Always turn off the device before cleaning and check the manufacturer's instructions for specific care guidelines.

Q: How long do TENS electrode pads last?

Electrode pads typically last for 20-30 applications before needing replacement, depending on skin oils, care practices, and quality. Store pads on their plastic backing in a sealed bag between uses to extend their lifespan.

Q: Can children use TENS machines?

TENS can be used for children under proper medical supervision with age-appropriate settings. Always consult a paediatric physiotherapist or doctor before using TENS with children.

Q: Is TENS safe after the first trimester of pregnancy?

TENS is generally considered safe after the first trimester but should only be used under healthcare supervision and never placed over the abdomen. Many maternity units offer TENS specifically designed for labour pain management.

Q: Can I use TENS alongside pain medications?

Yes, TENS can be safely used alongside most pain medications, potentially allowing for reduced dosage. The combination may provide more effective pain relief than either treatment alone.

Q: Is TENS better than heat or cold therapy?

Neither is universally "better" – they work through different mechanisms and may be complementary. TENS targets nerve pathways while heat/cold therapy affects blood flow and inflammation.

Q: What's the difference between dual-channel and quad-channel TENS machines?

Dual-channel TENS machines allow two areas to be treated simultaneously with two pairs of electrodes, while quad-channel devices can treat four areas at once. More channels offer greater versatility for complex or widespread pain.

Q: Are there wireless TENS options available?

Yes, wireless TENS units use Bluetooth technology to eliminate connecting wires between the control unit and electrode pads. These offer greater freedom of movement but typically cost more than traditional wired units.

Q: What should I do if my TENS machine isn't providing relief?

Consult your physiotherapist to verify correct pad placement, intensity settings, and treatment duration. Your condition may require different electrotherapy parameters or an alternative treatment approach.