Physiotherapy machines include TENS (transcutaneous electrical nerve stimulation) units, therapeutic ultrasound devices, electrical muscle stimulation (EMS) machines, interferential current (IFC) units, and laser therapy devices. Each machine works through a different mechanism to relieve pain, promote tissue healing, reduce inflammation, or strengthen muscles during rehabilitation. A landmark systematic review of 381 randomised controlled trials, known as the meta-TENS study and published in the BMJ, found that TENS was more effective than placebo for pain relief during or immediately after application, with a standardised mean difference of -0.96 and moderate-certainty evidence. This article explains what each physiotherapy machine does, how it works at the tissue level, how to use a TENS unit safely at home, and when your physiotherapist uses clinic-based machines as part of your treatment plan.

How to Use a Physiotherapy Machine

Using a physiotherapy machine correctly depends on which type of machine you are using, because each device delivers a different form of energy to the body for a different therapeutic purpose. TENS units deliver low-voltage electrical currents through the skin to block pain signals. EMS machines deliver stronger electrical currents that cause muscles to contract involuntarily. Therapeutic ultrasound delivers high-frequency sound waves into soft tissue to promote healing. Interferential current therapy delivers two medium-frequency electrical currents that cross inside the tissue to produce deep pain relief. Laser therapy delivers concentrated light energy at specific wavelengths to stimulate cellular repair.

Some physiotherapy machines are designed for home use. TENS units and basic EMS devices can be purchased over the counter and used at home with guidance from your physiotherapist. Other machines, including therapeutic ultrasound, interferential current, and clinical-grade laser therapy, require professional administration in a clinic setting because they involve parameters that must be calibrated to your specific condition. Your physiotherapy team determines which machines are appropriate for your treatment plan and teaches you how to use any home-based devices safely and effectively.

What Is a Physiotherapy Machine and What Does It Do?

A physiotherapy machine is any device used by a physiotherapist to deliver energy, whether electrical, acoustic, or light-based, into the body’s tissues for the purpose of relieving pain, accelerating healing, reducing inflammation, or restoring muscle function. Physiotherapy machines fall under the broader category of electrotherapy and modality-based treatments. They complement the hands-on manual therapy and therapeutic exercise that form the core of physiotherapy practice.

Physiotherapy machines serve four primary functions. Pain modulation machines, such as TENS and IFC, reduce the perception of pain by stimulating nerves in a way that blocks or modulates pain signals travelling to the brain. Tissue healing machines, such as therapeutic ultrasound and laser therapy, deliver energy that increases blood flow, stimulates collagen production, and accelerates the body’s natural repair processes at the cellular level. Muscle activation machines, such as EMS and neuromuscular electrical stimulation (NMES), produce involuntary muscle contractions that prevent atrophy, rebuild strength after surgery, and retrain motor patterns in weakened muscles. Anti-inflammatory machines, such as laser therapy and pulsed ultrasound, reduce swelling and inflammatory markers in acute and chronic conditions. Many machines serve multiple functions depending on the settings the physiotherapist selects.

How Does a TENS Machine Actually Work?

A TENS machine works by sending low-voltage electrical impulses through electrode pads placed on your skin, which stimulate sensory nerves to block pain signals from reaching your brain and trigger the release of endorphins, the body’s natural painkillers. The pain-blocking mechanism operates through the gate control theory of pain, first proposed by Melzack and Wall in 1965. The theory explains that non-painful sensory input, such as the tingling electrical stimulation from a TENS unit, activates large-diameter nerve fibres that inhibit pain signal transmission at the spinal cord level. The non-painful input essentially closes a neurological “gate” that blocks the pain message before it reaches the brain.

The endorphin release mechanism operates at higher intensities. When TENS is applied at a level strong enough to produce a comfortable buzzing or mild muscle twitch, the stimulation triggers the release of endorphins and enkephalins from the central nervous system. These neurotransmitters bind to opioid receptors in the brain and spinal cord, producing a natural analgesic effect that can outlast the stimulation session itself. The meta-TENS study, which analysed 381 randomised controlled trials, found that TENS was more effective than both placebo (SMD = -0.96, moderate-certainty evidence) and other pharmacological and non-pharmacological treatments (SMD = -0.72, low-certainty evidence) for pain relief during or immediately after application. A 2024 systematic review published in Frontiers in Pain Research confirmed that TENS, IFC, and EMS are all generally effective at reducing chronic low back pain after treatment.

What Is the Correct Way to Use a TENS Unit?

The correct way to use a TENS unit is to prepare your skin, connect the lead wires to the device, attach the electrode pads to clean skin around your painful area, turn the machine on, select the appropriate mode, and slowly increase the intensity until you feel a comfortable tingling sensation that is never painful. Following these steps in order prevents skin irritation, ensures proper electrical contact, and produces effective pain relief.

1. Wash and dry the skin where you plan to place the pads. Wipe the area with rubbing alcohol to remove oils, lotions, and sweat. Clean skin creates better contact between the electrode pads and your body, which ensures even electrical distribution and prevents hot spots that can cause burns.
2. Connect the lead wires to the TENS machine while the device is turned off. Plug the wires into the output channels on the machine, then snap or clip the other end of each wire securely into the electrode pads. Always connect wires before placing pads on your skin.
3. Place the electrode pads on your skin around the painful area. Position the pads at least 2.5 centimetres (1 inch) apart. Bracket the painful spot by placing pads on either side of it rather than directly on top of the most painful point. For massage therapy and muscle relaxation goals, some physiotherapists recommend placing pads directly over the target muscle belly.
4. Turn the TENS machine on and select your mode. Most home units offer a continuous mode and a burst or modulation mode. For general pain relief, continuous mode at standard sensory settings works well. Your physiotherapist can recommend the specific mode that suits your condition.
5. Increase the intensity slowly until you feel a strong but comfortable tingling or buzzing sensation. The sensation should be noticeable but never painful. A comfortable tingling indicates that the sensory nerve fibres are being stimulated to close the pain gate. Pain during TENS means the intensity is too high and should be reduced immediately.
6. Set the timer for 15 to 30 minutes. Sensory TENS for pain relief typically runs for 15 to 20 minutes per session. Your physiotherapist may recommend up to 30 minutes for certain conditions. You can repeat sessions 2 to 3 times per day with at least one hour between sessions.
7. Turn the machine off before removing the pads. Pulling pads off while the machine is still running can cause a sudden jolt of concentrated current on the skin. Always turn the intensity down to zero, then switch the unit off, then gently peel the pads from your skin.

The recommended settings for sensory TENS pain relief are a pulse duration of 50 to 80 microseconds, a frequency of 80 to 120 Hz, and an intensity adjusted to comfortable tingling, according to clinical guidelines used by River East Physiotherapy and confirmed by the NHS. These settings target the large-diameter sensory nerve fibres responsible for the gate control mechanism.

Where Should You Never Put a TENS Unit?

You should never put a TENS unit on your eyes, the front of your neck, directly over your heart, on broken or infected skin, on areas of numbness where you cannot feel the stimulation, or on any area with an active blood clot or malignant tumour. Placing TENS pads on the front of the neck can affect blood pressure and heart rate through stimulation of the carotid sinus. Placing pads directly over the heart poses a risk of cardiac arrhythmia. Areas of numbness are dangerous because you cannot gauge the intensity, which increases the risk of skin burns from excessive current.

• Over the eyes or directly on the eyelids
• On the front or sides of the neck (carotid sinus region)
• Directly over the heart or on the chest and back simultaneously
• On broken, irritated, infected, or sunburned skin
• Over areas of numbness or reduced sensation
• Over a deep vein thrombosis (DVT) or known blood clot
• Over a malignant tumour or cancerous tissue
• On the abdomen or lower back during pregnancy (unless directed by a healthcare provider)
• Near or over a cardiac pacemaker or implanted defibrillator

People with epilepsy should consult their physician before using TENS, as electrical stimulation may trigger seizures in some individuals. The NHS recommends checking with a GP or physiotherapist before using TENS for the first time, particularly if you have any pre-existing medical conditions.

How Long Is Too Long to Use a TENS Unit?

Using a TENS unit for longer than 30 minutes per session provides diminishing returns and increases the risk of skin irritation beneath the electrode pads. Most clinical guidelines recommend 15 to 30 minutes per session for sensory TENS. You can use TENS multiple times per day, typically 2 to 3 sessions with at least 60 minutes between sessions, but each individual session should stay within the 30-minute window. Extended continuous use can desensitise the nerve fibres being stimulated, which reduces the pain-relieving effect. It can also cause the adhesive on the electrode pads to break down, creating gaps in contact that concentrate the electrical current and increase the risk of localised skin burns.

Does TENS Heal or Just Mask Pain?

TENS primarily provides temporary pain relief rather than directly healing the underlying tissue injury, but the pain relief it provides creates conditions that support the healing process. The meta-TENS study confirmed that the pain-relieving effect of TENS occurs during and immediately after application, which classifies it as a symptomatic treatment rather than a curative one. The electrical stimulation does not repair torn muscle fibres, regenerate damaged cartilage, or reverse degenerative changes in joints.

The indirect contribution to healing is significant. Patients who use TENS for pain relief between exercise rehabilitation sessions are more likely to perform their prescribed exercises consistently because their pain is better managed. Consistent exercise drives tissue adaptation, strengthening, and functional recovery. A 2024 systematic review published in Cureus found that TENS in emergency department settings not only reduced pain but also decreased anxiety and improved patient satisfaction, both of which support engagement with ongoing treatment. TENS is most effective as one component of a comprehensive physiotherapy programme that includes manual therapy, therapeutic exercise, and patient education, not as a standalone treatment.

Does a TENS Unit Speed Up Healing?

A TENS unit does not directly speed up tissue healing, because its primary mechanism targets nerve stimulation for pain relief rather than cellular repair. The evidence for TENS accelerating structural healing is limited compared to the strong evidence for its pain-relieving effects. Some research suggests that the increased blood flow produced by TENS at motor-level intensities may modestly support the delivery of nutrients and oxygen to injured tissue, but this effect is secondary to the main therapeutic purpose. For direct tissue healing acceleration, modalities such as therapeutic ultrasound and laser therapy are more appropriate because they deliver energy that directly stimulates cellular repair processes.

Does TENS Loosen Tight Muscles?

TENS can help loosen tight muscles indirectly by reducing the pain that causes muscle guarding and spasm, but it does not produce the same direct muscle relaxation effect as manual therapy or targeted stretching. When pain decreases, the nervous system reduces its protective muscle tightening response, which allows the tissue to relax. At higher intensities, TENS may produce visible muscle twitching, but this twitching is a side effect of the electrical current reaching motor nerves rather than a targeted therapeutic action. EMS (electrical muscle stimulation) is the modality specifically designed to activate and relax muscles through controlled involuntary contractions. Your physiotherapist selects the right modality based on whether the goal is pain relief (TENS), muscle activation (EMS), or both.

What Is the Difference between TENS and EMS?

The difference between TENS and EMS is that TENS stimulates sensory nerves to block pain signals and trigger endorphin release for pain relief, while EMS stimulates motor nerves to produce involuntary muscle contractions for strengthening, atrophy prevention, and motor retraining. TENS uses lower-intensity currents that you feel as tingling or buzzing on the skin surface. EMS uses stronger currents that cause visible, rhythmic muscle contractions. Both technologies use electrode pads placed on the skin, but the target tissue, the intensity, and the therapeutic goal are fundamentally different.

Machine Type	How It Works	Primary Purpose	Home Use?	Session Duration
TENS	Low-voltage electrical impulses stimulate sensory nerves to block pain signals	Pain relief	Yes	15-30 minutes
EMS / NMES	Stronger electrical impulses stimulate motor nerves to produce muscle contractions	Muscle strengthening, atrophy prevention	With guidance	15-20 minutes
Therapeutic Ultrasound	High-frequency sound waves (1-3 MHz) penetrate tissue to increase blood flow and stimulate repair	Tissue healing, inflammation reduction	No (clinic only)	5-10 minutes per area
Interferential Current (IFC)	Two medium-frequency currents (4,000 Hz) cross inside tissue to produce deep low-frequency stimulation	Deep pain relief, swelling reduction	No (clinic only)	15-20 minutes
Class IV Laser Therapy	Concentrated light energy at 800-980 nm wavelength stimulates cellular photobiomodulation	Cellular repair, inflammation reduction, pain relief	No (clinic only)	5-15 minutes per area

Sources: BMJ (meta-TENS study, Johnson et al., 2022), Frontiers in Pain Research (Wolfe et al., 2024), Gymna (therapeutic ultrasound clinical standards), NHS UK

Many patients benefit from more than one modality during their recovery. A post-surgical knee patient may use EMS to prevent quadriceps atrophy in the early weeks, TENS for pain management between sessions, and therapeutic ultrasound to accelerate scar tissue remodelling. The physiotherapist selects and sequences modalities based on the patient’s stage of recovery, their specific goals, and the evidence supporting each intervention for their condition.

How to Use a Physiotherapy Ultrasound Machine

A physiotherapy ultrasound machine is used by applying a water-based coupling gel to the skin, then moving a handheld transducer in slow circular or overlapping strokes over the treatment area while the machine delivers high-frequency sound waves into the tissue beneath. Therapeutic ultrasound operates at frequencies of 1 to 3 MHz. A frequency of 1 MHz penetrates tissue to a depth of 3 to 5 centimetres, making it suitable for deep structures such as hip joints, lumbar spine muscles, and deep tendon injuries. A frequency of 3 MHz penetrates only 1 to 2 centimetres, making it better suited for superficial injuries such as lateral epicondylitis, Achilles tendinopathy, and wrist sprains, according to clinical standards published by Gymna.

Therapeutic ultrasound produces two types of effects in tissue. Thermal effects occur when continuous-wave ultrasound raises the temperature of the target tissue by 1 to 4 degrees Celsius, which increases collagen extensibility, blood flow, and metabolic rate. Non-thermal (mechanical) effects occur when pulsed ultrasound produces microscopic vibrations called acoustic streaming and cavitation that stimulate cellular activity, increase membrane permeability, and accelerate the inflammatory and proliferative phases of tissue repair. A 2021 randomised pilot trial published in PMC found that continuous ultrasound at 1 MHz significantly increased forearm blood flow compared to placebo (2.96 vs 2.09 mL/min/100 mL, p < 0.05).

Therapeutic ultrasound is a clinic-based modality administered by a trained physiotherapist or chiropractic practitioner. It is not available for home use because the parameters, including frequency, intensity, duty cycle, and treatment duration, must be set precisely for each patient and each condition. Incorrect settings can cause tissue overheating or fail to deliver a therapeutic dose. Sessions typically last 5 to 10 minutes per treatment area.

What Is Interferential Current Therapy?

Interferential current (IFC) therapy is a clinic-based electrotherapy modality that uses two medium-frequency electrical currents, typically set at approximately 4,000 Hz, delivered through four electrode pads arranged so the currents cross inside the tissue at the treatment site. Where the two currents intersect, they produce a lower-frequency beat pattern (typically 1 to 150 Hz) that penetrates deeper than surface-level TENS stimulation. This deep penetration makes IFC particularly effective for pain relief in structures that sit beneath layers of muscle and fat, such as the lumbar spine, hip joint, and deep shoulder muscles.

IFC reduces pain through the same gate control mechanism as TENS but reaches deeper tissue layers due to the medium-frequency carrier wave. The higher carrier frequency encounters less skin resistance than the low-frequency current used by TENS, which allows the therapeutic current to travel further into the body before it produces its pain-relieving effect. IFC also promotes local blood flow and reduces swelling in the target area. A 2024 systematic review in Frontiers in Pain Research confirmed that IFC is effective at reducing chronic low back pain, supporting its use as part of a multidisciplinary treatment approach alongside acupuncture and manual therapy.

What Is Laser Therapy in Physiotherapy?

Laser therapy in physiotherapy uses concentrated light energy at specific wavelengths, typically 800 to 980 nanometres for Class IV therapeutic lasers, to stimulate a process called photobiomodulation at the cellular level. The photon energy absorbed by the cells increases the production of adenosine triphosphate (ATP), the molecule that powers cellular repair, replication, and function. Increased ATP production accelerates tissue healing, reduces inflammation, and decreases pain by modulating inflammatory mediators and stimulating the release of endorphins.

Laser therapy at our clinic uses a Class IV K-Laser, which delivers higher power output than lower-class laser devices and can treat larger and deeper areas of tissue in shorter sessions. Class IV lasers penetrate through skin, subcutaneous fat, and muscle to reach deep structures such as joint capsules, tendons, and ligaments. Sessions typically last 5 to 15 minutes per treatment area, depending on the size of the area and the depth of the target tissue. Laser therapy is completely non-invasive, produces no sensation beyond a mild warmth, and carries minimal side effects when administered by a trained practitioner. Patients at our Markham clinic commonly receive laser therapy alongside manual therapy, therapeutic exercise, and custom orthotics for a comprehensive treatment approach.

Is There a Downside to Using a TENS Unit?

The downsides of using a TENS unit are that it provides temporary pain relief rather than a permanent cure, it can cause skin irritation or burns if the electrode pads are not properly maintained, and it is not effective for every type of pain or every patient. TENS works best for musculoskeletal pain, period pain, arthritis pain, and certain types of neuropathic pain. It is less effective for deep visceral pain and pain caused by central nervous system conditions.

Skin irritation is the most common side effect. The adhesive on electrode pads can cause redness, itching, or mild rash in patients with sensitive skin. Rotating pad placement sites between sessions and using hypoallergenic pads reduces this risk. The most serious home-use injury is a skin burn caused by incomplete pad contact, where the electrical current concentrates through a smaller area of skin than intended, according to River East Physiotherapy. Ensuring full pad contact with the skin at all times and replacing worn pads promptly prevents burns. Patients who use TENS as their only form of treatment without following a physiotherapy programme that includes exercise and manual therapy are unlikely to see long-term improvement.

Can You Use a TENS Machine at Home?

Yes, you can use a TENS machine at home, and many physiotherapists prescribe home TENS use as part of a broader pain management strategy. Home TENS units are available at pharmacies and online retailers. Look for a device with a CE or CSA certification mark, adjustable intensity and frequency settings, a timer function, and clear instructions. Your physiotherapist can recommend a specific model, demonstrate the correct pad placement for your condition, and prescribe the settings that are most likely to produce effective pain relief for your particular pain pattern.

Home TENS use works best when it supplements rather than replaces your in-clinic physiotherapy sessions. Using TENS between appointments helps manage pain so you can perform your prescribed home exercises more comfortably. The exercises drive the structural adaptation, strengthening, and functional recovery that TENS alone cannot produce.

Do Doctors Recommend TENS Machines?

Yes, doctors and physiotherapists recommend TENS machines for appropriate patients as a safe, drug-free pain management option supported by a large body of clinical evidence. The meta-TENS study, the largest systematic review of TENS research ever conducted, analysed 381 randomised controlled trials involving adults with acute and chronic pain across a wide range of conditions. The study found moderate-certainty evidence that TENS is more effective than placebo for pain relief. The NHS in the United Kingdom includes TENS as a recommended treatment option for various types of pain. Approximately 70% of emergency department patients report pain as a primary symptom, according to a 2024 review in Cureus, and TENS has been evaluated as a non-pharmacological alternative in these high-demand settings with positive results for pain reduction, anxiety reduction, and patient satisfaction.

TENS is not appropriate for everyone. Patients with pacemakers, certain cardiac conditions, epilepsy, or active malignancies should not use TENS without explicit medical clearance. Pregnant patients should avoid TENS on the lower back and abdomen unless directed by their healthcare provider. For all other patients, TENS represents a low-risk, evidence-supported physiotherapy tool that complements exercise, manual therapy, and other modalities within a comprehensive rehabilitation plan.

Frequently Asked Questions

How Many Times a Day Can You Do Electrical Stimulation?

You can do electrical stimulation with a TENS unit 2 to 3 times per day, with at least 60 minutes between sessions and each session lasting 15 to 30 minutes. EMS (muscle stimulation) is typically applied once or twice daily, depending on the muscle group and the treatment goal. Your physiotherapist sets the frequency based on your condition, your tolerance, and the specific type of electrical stimulation being used.

How Long Does It Take to Feel the Benefits of a TENS Machine?

Most patients feel the pain-relieving benefits of a TENS machine within the first 5 to 10 minutes of a session, as the tingling sensation activates the gate control mechanism that blocks pain signals. The endorphin-mediated effect, which produces a deeper and longer-lasting reduction in pain, typically develops within 20 to 30 minutes. Some patients experience pain relief that lasts several hours after the session ends, while others notice the pain returning shortly after the machine is turned off.

Is Therapeutic Ultrasound Safe?

Yes, therapeutic ultrasound is safe when administered by a trained physiotherapist who selects the correct frequency, intensity, and duration for your condition. Contraindications include application over malignant tumours, active infections, metal implants in the treatment area, the eyes, reproductive organs, growth plates in children, and areas with impaired circulation or sensation. Your physiotherapist screens for contraindications before using ultrasound in your treatment.

Can You Use a TENS Machine during Pregnancy?

You can use a TENS machine during pregnancy for labour pain under the guidance of your midwife or healthcare provider, but you should not place TENS pads on your lower back or abdomen during pregnancy outside of active labour. TENS is commonly used during labour as a drug-free pain relief option, particularly in the early stages. The NHS includes TENS as a recommended option for labour pain management. Always consult your healthcare provider before using TENS at any stage of pregnancy.

What Is the Best Physiotherapy Machine for Back Pain?

The best physiotherapy machine for back pain depends on the cause and stage of your pain. TENS is effective for temporary pain relief during daily activities and between treatment sessions. IFC provides deeper penetration for pain originating from structures beneath the surface muscles of the back. Therapeutic ultrasound supports tissue healing in acute soft tissue injuries. Laser therapy reduces inflammation and stimulates cellular repair in chronic conditions. Your physiotherapist assesses your specific condition and recommends the modality or combination of modalities that best matches your needs.

The Takeaway

Physiotherapy machines are valuable tools that complement manual therapy and therapeutic exercise within a comprehensive rehabilitation programme. TENS provides safe, evidence-based pain relief that you can use at home between appointments. Therapeutic ultrasound, interferential current, and laser therapy deliver clinic-based treatments that accelerate healing, reduce inflammation, and address pain at deeper tissue levels. Understanding how each machine works and when it is appropriate helps you get the most from your treatment and stay engaged with your recovery.

If you have questions about which physiotherapy modalities are right for your condition, our team at KC Rehab can assess your needs and build a treatment plan that includes the right combination of hands-on therapy, exercise, and machine-based modalities. Call us at 905-205-1668 or book an assessment online.