Electrotherapeutic Modalities: TENS, Ultrasound, and Stimulation in Physiotherapy

Electrotherapeutic Modalities: TENS, Ultrasound, and Stimulation in Physiotherapy

Electrotherapeutic modalities include TENS, therapeutic ultrasound, and interferential currents. TENS delivers an electrical current through adhesive pads, known as electrodes. Ultrasound delivers sound waves. These devices raise questions about how they work, their risks, and their role in physical therapy.

At Physioactif, treatment is based on assessment, explanations, and exercises tailored to your activities. Manual therapy may also be part of the treatment plan. A review recommends exercise as the first-line treatment for muscle or joint pain caused by movement.¹ Another review examines the use of assistive devices in conjunction with exercise for knee osteoarthritis, a condition that affects the cartilage and other tissues of the joint. Cartilage covers the ends of the bones in a joint.²

This article describes the devices, the mechanisms under study, research on specific health issues, and precautions to be aware of. Electrotherapy treatments are not a substitute for a professional evaluation or a tailored physical therapy program.

What are electrotherapy modalities?

Electrotherapeutic modalities deliver an electric current or sound waves to the body. TENS and interferential currents use an electric current; ultrasound uses sounds that are inaudible to the human ear. Research on TENS focuses, in particular, on nerve activity.³ Research on ultrasound also examines the reactions of cells exposed to these waves.⁴

Electrotherapy is a passive treatment: the device delivers energy without requiring you to perform an exercise. In contrast, during a therapeutic exercise, you actively participate in the movement. At Physioactif, your participation and your goals guide your treatment.

The three main methods

TENS stands for transcutaneous electrical nerve stimulation, which is the stimulation of nerves through the skin. The device delivers electrical impulses through adhesive electrodes. Its use usually produces a tingling sensation. If you experience pain, turn off the device and speak with a healthcare professional.

Therapeutic ultrasound often uses frequencies of 1 or 3 MHz, or one or three million vibrations per second. These waves interact with tissues and can generate heat within them.⁵ Experiments also measure blood flow—that is, the amount of blood circulating—particularly in ten healthy adults.⁶ These physical measurements and studies on patients’ pain address different questions.⁷

Interferential currents cause two electric currents to meet. An experiment conducted on 20 people who already had electrodes implanted compared the electrical voltages measured at depth. The values were higher with interferential currents than with TENS.⁸ This measurement does not support a conclusion that there is a benefit for the patient. Other studies focus on pain rather than on the depth of the current.⁹

Role in the treatment plan

The physical therapy plan begins with your symptoms, your abilities, and the activities you want to be able to do again. The physical therapist explains the problem to you, selects the exercises, and adjusts the progression of your treatment. A machine cannot replace these steps.

Any recent pain that significantly limits your movement warrants an evaluation. Studies on TENS do not cover all possible causes of this pain. The 2015 Cochrane review focused on various types of acute pain; the large 2022 review primarily examined pain during or immediately after application.^{10, 11} This research does not replace identifying the cause of your symptoms.

For capsulitis—a condition in which the shoulder becomes painful and stiff—the 2014 Cochrane review did not allow for a clear conclusion regarding the addition of ultrasound to exercise therapy. The certainty of the evidence was very low.¹²

How do electrotherapy modalities work?

Electrotherapeutic modalities deliver impulses to the nerves or vibrations to the tissues, depending on the device. Researchers are studying the neural pathways for TENS and the physical interactions with tissues for ultrasound.^{3, 13}

TENS: Mechanisms Under Study

Research on TENS focuses in particular on two components of the nervous system: the transmission of signals in the spinal cord and the role of substances produced by the body. The spinal cord is the nerve cord located within the spine that transmits signals between the brain and the body.

The gate control theory describes how different nerve signals interact in the spinal cord. Nerve fibers—the extensions that transmit these signals—provide the nervous system with information about touch. Others respond to situations that may threaten tissues. Neural circuits can either inhibit or amplify the transmission of these signals.¹³ The “gate” is a metaphor used to explain these interactions, not an actual door.

The sensations of touch and pain are therefore not simply the result of a race between two nerves. The brain and spinal cord process multiple types of information simultaneously. Studies on these neural circuits and those that measure pain while using a device are distinct.^{13, 11}

Opioids produced by the body are substances—including endorphins—that play a role in pain control. Researchers are studying their role in responses to different frequencies of electrical stimulation.^{3, 14} Frequency refers to the number of pulses per second. Intensity refers to the strength of the current. These settings are not interchangeable.

A tingling sensation or muscle contraction indicates that stimulation is being received. It is not a measure of injury repair.

Ultrasound: Physiological Mechanisms

Ultrasound waves can be emitted continuously, in continuous mode, or with pauses, in pulsed mode. The frequency of the waves, their intensity, and these pauses determine the tissue exposure.

A trial involving 221 people with shoulder pain compared real ultrasound treatment to a simulated device, known as a placebo. Both groups also received advice, home exercises, and manual therapy. The addition of real ultrasound did not show any superiority over the placebo at follow-up visits up to six months later.¹⁵

Mechanical interactions involve the very small vibrations and movements produced when waves pass through tissue. Experiments study cellular responses and interactions with the surrounding environment.⁴ A result obtained from cells alone does not prove that a person will recover better. Clinical studies examine pain and activities separately.¹⁶

The thermal effect is the heat produced when tissues absorb some of the sound energy.⁵ Researchers measured a rise in muscle temperature in 18 healthy adults.¹⁷ Others measured blood flow in ten healthy adults.⁶ These experiments do not prove a therapeutic effect. In the shoulder pain trial described above, the addition of ultrasound was no more effective than a placebo.¹⁵

Laboratory research and patient trials do not evaluate the same things. The former examine, among other things, cellular responses; the latter measure pain, movement, and the ability to perform activities.^{4, 16}

What conditions do studies on these devices examine?

Studies on these devices focus, in particular, on pain in the lower back, neck, knee, and shoulder. These conditions require different assessments. To learn about the available treatment options, see our guides on lumbar pain(lower back pain) and cervical pain(neck pain).

Research on TENS

A review of chronic low back pain—persistent pain in the lower back—rats the certainty of its findings as very low.¹⁸ For chronic neck pain, a Cochrane review also concludes that there is significant uncertainty.¹⁹ These populations are not the same as those with a recent injury. Lower back pain following physical exertion or mid-back pain requires its own evaluation.

A 2026 review on knee osteoarthritis compares several TENS settings and several types of comparator treatments.²⁰ The focus of this review is the knee; its conclusions should not be automatically applied to hip or back osteoarthritis. The physical therapy plan takes into account the joint and your difficulties with daily activities.

For carpal tunnel syndrome, which affects a nerve in the wrist, a 2018 review summarizes various devices and procedures.²¹ The included studies did not allow for the determination of optimal settings and did not examine long-term effects. This review does not constitute a protocol for all sprains, tendon pain, or post-surgical pain.

Research on Ultrasound

Tendinopathies are disorders of the tendons, the structures that connect muscles to bones. For shoulder tendons, a review found no benefit from ultrasound compared to a placebo or counseling.¹⁶ Forepicondylitis—pain in the tendons on the outer side of the elbow—another review found no clear difference compared to other treatments.²² Tendon problems in the knee or the Achilles tendon, behind the ankle, are not covered by these two reviews. For calcific tendinitis of the shoulder—which involves calcium deposits in a tendon—one trial distinguished several measures: deposit size, pain, strength, and difficulty with daily activities.²³ A change in the size of a deposit and a change in pain are two distinct outcomes.

Chronic bursitis—a persistent inflammation of a small sac surrounding a joint—and adhesive capsulitis, or frozen shoulder, are different conditions. Localized swelling, inflammation, or persistent involuntary muscle contractions should also be evaluated. The name of a symptom alone is not enough to choose a device.

An injury to a tendon or ligament—such as a scar resulting from an injury—requires a treatment plan tailored to the affected tissues. Ligaments connect bones to one another. Safety guidelines and the progression of movements depend on the specific injury; this article does not recommend ultrasound for repairing or softening these tissues.

For the recent fractures studied, a review of randomized controlled trials concluded that low-intensity pulsed ultrasound does not improve key patient outcomes, such as return to work, pain, or the need for further surgery.²⁴ This conclusion does not necessarily apply to all situations involving bone healing.

Important Contraindications

For TENS: Do not use the device if you have a pacemaker—an implanted device that helps the heart beat—or epilepsy. During pregnancy, do not use it without consulting your doctor or midwife. NHS safety guidelines specify these restrictions. Active or suspected thrombosis—that is, a blood clot in a vein—also precludes electrical stimulation, even at a distance from the clot, according to Canadian recommendations on precautions.

For therapeutic ultrasound: specifically avoid the abdomen and lower back during pregnancy; areas with known or suspected cancer; active blood clots; the eyes; reproductive organs, including the testicles; and implanted electronic devices. An infection, heart disease, or an area of bone growth in a child requires a professional decision regarding the treatment site and settings. Certain situations preclude the use of ultrasound; others require precautions. Canadian recommendations on precautions distinguish between these cases. This list is not a substitute for a professional evaluation.

What happens during an electrotherapy session?

An electrotherapy treatment involves assessing risks, preparing the skin, and adjusting the device. TENS uses electrodes; ultrasound uses a transducer and gel. The practitioner monitors the patient’s sensations during the treatment. This description explains the procedure but does not constitute a treatment recommendation at Physioactif.

A typical TENS session

The preliminary assessment focuses on your symptoms, your health, and your skin. The practitioner checks for any contraindications—that is, situations in which the device could pose a risk. The practitioner then determines the settings and the treatment area.

The skin must be clean. The electrodes are placed according to the device and the instructions provided. The device must be turned off while the electrodes are being applied; the number and placement of the electrodes are not chosen at random.

During treatment, the intensity gradually increases until a non-painful tingling sensation is felt. If you experience pain, a burning sensation, or irritation, stop the device and notify the practitioner. Through discussion, the treatment can be adjusted or stopped. The information sheet from the Cambridge University Hospital describes the settings and sensations to monitor.

A typical ultrasound exam

Before performing the ultrasound treatment, the practitioner checks the treatment area, the skin, sensitivity, and any contraindications. The choice between continuous and pulsed modes is part of the device's settings.

The gel acts as a conductor between the device's head and the skin to transmit the waves. The head should be kept moving while the device is applied to the skin, in accordance with Health Canada's safety guidelines.

Continuous mode may cause a sensation of warmth, whereas pulsed mode usually does not produce any noticeable warmth. Warmth is not a sign that the tissue is healing. Report any pain or burning sensation immediately.

Treatment Frequency and Duration

The duration and settings vary depending on the device and the situation. They cannot be determined based on a universal number of sessions. The professional must explain the procedure and reassess each treatment.

Before using a personal device, consult a licensed professional.The Quebec Order of Physiotherapists reminds the public that these devices pose risks when used without the necessary expertise.

What are some frequently asked questions about electrotherapy treatments?

Frequently asked questions about electrotherapy treatments include their effectiveness, the duration of sessions, how they feel, home use, insurance coverage, risks, and differences between devices.

Is electrotherapy really effective?

The effectiveness of a device depends on the condition being studied and the treatment it is being compared to. At Physioactif, we prioritize explanations, movement, and tailored exercises. The results of a study on a device should be distinguished from those of a comprehensive physical therapy program.

Not all reviews on TENS ask the same question. The 2015 review focused on acute pain and identified significant limitations in the quality of the trials.¹⁰ The 2022 review covered a variety of conditions and focused primarily on pain during or immediately after application.¹¹ For knee osteoarthritis, a 2024 review found no clinically significant additional benefit from adding TENS to exercise, compared to exercise alone or exercise combined with a sham device.²

Research on ultrasound focuses on various conditions, including the knee and shoulder.⁷ A study on calcific tendinitis does not provide answers for all types of tendon pain.²³ Your evaluation is still necessary to choose the appropriate treatment and exercises.

Exercise can reduce muscle or joint pain caused by movement.¹ For knee osteoarthritis, the 2024 review found no clinically significant additional benefit from adding TENS, interferential currents, or ultrasound to exercise.² This comparison does not justify adding these therapies routinely. It does not call into question the benefits of exercise.

How long does a session last?

The duration varies depending on the protocol studied. As a general guide, a review on neck pain reports TENS applications lasting 20 to 60 minutes.¹⁹ A trial on calcific tendinitis used 10 minutes of ultrasound per session.²³ A trial on the knee used 20 minutes of interferential currents.²⁵ These study durations are not intended as guidelines for self-treatment.

The duration of a physical therapy appointment includes the evaluation, explanations, and other procedures. Please confirm the expected duration with the clinic when you make your appointment.

Does it hurt?

The application should not cause any pain. A tingling sensation caused by TENS is not the same as a burning sensation.

TENS typically produces a tingling or prickling sensation. Continuous-wave ultrasound may produce a sensation of warmth; pulsed-wave ultrasound may not produce any noticeable sensation. The absence of sensation does not indicate whether the setting is safe.

If you experience pain, significant discomfort, or a burning sensation, notify your therapist immediately.

Can you use a TENS machine at home?

TENS devices are sold for home use. Consult a professional first to assess the risks and understand the manufacturer’s instructions.The Quebec Order of Physiotherapists recommends this consultation before using an electrotherapy device at home.

Home TENS therapy is not a substitute for your exercise program or professional care. Do not use it on broken, infected, or numb skin; on the neck; near the mouth or eyes; or simultaneously on the chest and back. Also avoid using it while sleeping, in water, while driving, or while operating machinery. Refer to the NHS safety guidelines and the manufacturer’s instructions.

Is electrotherapy covered by insurance?

Reimbursement depends on your insurance policy. Check with your insurer to confirm which treatments are covered and what documents are required. Also ask the clinic about the rates and applicable fees;the Ordre professionnel de la physiothérapie du Québec specifies that the professional must inform you of the cost of care.

Physical therapy provided through the public healthcare system is covered by public insurance. At private clinics, reimbursement depends on your coverage and, depending on the situation, on a specific public program. Check your coverage details before your appointment.

Are there any side effects?

Studies on TENS primarily report mild adverse effects, such as irritation or redness. Reporting of these effects remains incomplete, which limits the ability to estimate their frequency.¹¹

If your skin itches, becomes red, or becomes irritated, turn off the TENS device and remove the electrodes. If you experience sensitivity to the adhesive, consult a healthcare professional before using the device again.

When using ultrasound, any pain or burning sensation requires that you stop the treatment and have your skin checked. The fact that no serious side effects were reported in a study does not guarantee the absence of risk, especially if your skin’s sensitivity is reduced.

Always tell your therapist about any unusual reactions.

How many sessions are needed?

The number of physical therapy sessions depends on your condition, your goals, and how your abilities progress. The physical therapist will reassess the activities that are important to you, such as walking, working, or raising your arm.

Your exercise program remains central to your treatment. A discussion with your physical therapist will allow us to adjust your care if your needs or symptoms change.

What is the difference between TENS and interferential currents?

TENS delivers pulses through electrodes placed on the skin. Interferential currents use currents that change direction at similar frequencies and meet. The difference lies in the current produced, not in the presence or absence of electrodes.

The starting frequencies of interferential currents are often a few kilohertz, or a few thousand cycles per second. One study compared 2,000, 4,000, and 8,000 Hz.²⁵ The in-depth measurement experiment described above does not demonstrate that a higher electrical voltage improves clinical outcomes.⁸

Devices also differ in terms of their settings and safety guidelines. Any comparison must take into account the model being used and the health issue being assessed.

What are the key points to remember about electrotherapy techniques?

Electrotherapy modalities are devices whose operation, risks, and outcomes vary depending on the specific technique used. At Physioactif, your care is guided by an assessment, detailed explanations, and tailored exercises. These exercises have been shown to provide relief from certain types of pain caused by movement.¹

If pain persists or limits your activities, a physical therapy evaluation can help identify your difficulties and develop a tailored program. Do not use a device to delay the evaluation of a new or unexplained symptom.

Understanding the anatomy of the spine helps you locate the structures of the back. For a lumbar herniated disc—where part of a disc between the bones in the lower back slips out of place—or other back problems, the evaluation focuses on your symptoms, your range of motion, and the activities you’d like to resume.

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