Ultrasound in physiotherapy delivers high-frequency sound waves into soft tissue to generate heat, increase local blood flow, and relax muscle and connective tissue. The waves sit above the range of human hearing, and a physiotherapist applies them through a handheld transducer pressed against the skin with a layer of coupling gel. Below we explain how the machine produces those waves, how deep they reach at different frequencies, what a session feels like, how long treatment takes, what the published evidence actually shows for pain and tendon healing, who should avoid the treatment, and why we use Class IV K-Laser therapy at our clinic rather than ultrasound.

What Does Ultrasound Do in Physiotherapy?

Ultrasound in physiotherapy does two things to tissue: it heats the tissue and it agitates the fluid inside it. Heating is the thermal effect, and agitation is the mechanical effect, and every application of therapeutic ultrasound produces some blend of the two depending on the settings the clinician selects.

Selecting settings determines which effect dominates. According to StatPearls, published by the National Library of Medicine, the thermal effect raises the temperature of deeper tissues such as muscle and fascia, and that temperature rise induces dilation of blood vessels. Dilated blood vessels increase cellular metabolism by delivering more oxygen and nutrients to the treated area. This warming and dilation is the mechanism behind ultrasound diathermy, which clinicians have used for muscle relaxation for decades. Physiotherapists have applied therapeutic ultrasound for pain management since the 1930s, which makes it one of the oldest electrotherapy modalities still found in clinics.

Clinics still using it typically apply it alongside hands-on treatment rather than on its own. That combined approach is standard across the profession, since no passive modality rebuilds strength or corrects movement by itself. Our own physiotherapy follows the same principle, pairing manual therapy with graded exercise so the gains from any passive treatment actually hold.

How Does an Ultrasound Machine Produce Sound Waves?

An ultrasound machine produces sound waves through the piezoelectric effect, where an electrical signal makes crystals inside the probe head vibrate. Crystals inside the probe head convert that electrical signal into mechanical vibration, and the vibration creates waves at frequencies outside the range of human hearing, which spans roughly 20 hertz to 20,000 hertz.

Frequencies above 20,000 hertz cannot travel efficiently from a vibrating probe into the body through air. Air is the reason coupling gel exists. A hypoallergenic gel is spread across the skin before treatment, and the gel conducts the waves into the tissue in an efficient, predictable pattern. StatPearls notes that various coupling mediums have been tested and hypoallergenic gels produce the strongest wave transduction with minimal interference. Without gel, most of the energy reflects off the skin surface and never reaches the tissue underneath.

Reaching the tissue underneath is only half the task, because the energy must also be spread evenly. The clinician keeps the transducer moving in a slow stroking motion across the treatment area for the entire session, which prevents energy concentrating in one spot. Concentrated energy in one spot is what causes superficial burns, the main complication associated with the technique. Anyone considering this modality is worth reading about alongside a broader picture of physiotherapy treatment as a whole, since passive modalities represent a small slice of what physiotherapy involves.

How Deep Does Ultrasound Therapy Penetrate?

Ultrasound therapy penetrates to different depths depending on frequency, and 1 MHz reaches deeper tissue while 3 MHz treats more superficial tissue. StatPearls sets the musculoskeletal treatment range at 1 to 3 MHz with an intensity of 1.0 watt per square centimetre, and states that the provider changes the frequency specifically to change the tissue depth affected.

Changing the depth affected is a deliberate clinical decision rather than a machine default. A superficial tendon near the wrist calls for 3 MHz, while a muscle sitting several centimetres below the surface calls for 1 MHz. Depth alone does not determine how much energy the tissue absorbs, however. Tissue composition matters just as much, and StatPearls reports that tissues containing a higher content of proteins, meaning muscle and bone, absorb the energy from the mechanical waves at a higher rate than tissues with higher water content such as fat.

Higher water content absorbs less, which means the same settings produce different results in different patients and different body regions. Variable absorption across body types is one reason results with this modality are inconsistent, and it is a limitation rarely mentioned on clinic pages. Depth of reach is also where light-based treatment differs sharply, since deep tissue laser treatment uses specific wavelengths chosen for penetration rather than a frequency dial.

What Does Ultrasound Feel Like During Treatment?

Ultrasound feels like mild warmth and a light gliding pressure, and it does not hurt. Warmth is the sensation most patients report, produced by the thermal effect raising tissue temperature slightly beneath the probe. Some patients feel almost nothing at all, particularly at lower intensities or when the settings favour the mechanical effect over the thermal one.

Settings that favour the mechanical effect generate less heat and therefore less sensation, which sometimes leaves patients wondering whether the machine is working. Working correctly and feeling dramatic are different things with this treatment. The probe stays in continuous motion throughout, so the sensation moves across the area rather than sitting in one place, and the gel feels cool on first contact before warming.

Cool gel and gentle warmth make the session comfortable enough that no anaesthetic or preparation is needed. No preparation means the treatment slots easily into a longer appointment. A clinician typically applies it while the patient is positioned comfortably, then wipes the gel away and moves directly into hands-on work or exercise for the remainder of the visit.

How Long Is an Ultrasound Therapy Session?

An ultrasound therapy session runs roughly 3 to 10 minutes per treatment area. The StatPearls musculoskeletal protocol specifies approximately 10 minutes of application per area, after which the clinician wipes the gel from the skin, while shorter applications of 3 to 5 minutes per area are also used in practice.

Practice varies because no single protocol has been established as superior across conditions. Variation in protocol is itself part of why the evidence base is difficult to interpret, since trials using different durations, frequencies, and intensities cannot be compared cleanly. Trials that differ in dose are effectively testing different treatments under one name.

One name covering many doses also means ultrasound is almost never the whole appointment. The rest of the visit carries the clinical weight, and passive modalities such as this one function as a preparation step before manual therapy or loading. Preparation of the tissue is a reasonable role for it, and that is the role most contemporary clinicians assign it.

Does Ultrasound Therapy Reduce Pain?

Ultrasound therapy reduces pain in some patients, and the strongest supporting study recorded visual analogue pain scores falling by approximately 4 points. Muftic and Miladinovic, publishing in Acta Informatica Medica in 2013, compared two groups receiving low-intensity ultrasound at different power settings in patients with chronic limb or spine pain, and both groups improved by roughly that margin.

That margin is clinically meaningful on a 0 to 10 scale, but the study sits at level III evidence, which StatPearls records as the ceiling of support for low-intensity ultrasound in degenerative musculoskeletal disorders. Level III evidence means the finding comes from studies without randomisation or blinding strong enough to rule out other explanations. Other explanations matter here, because the treatment is applied by a clinician who is also touching the patient, warming the tissue, and providing attention over ten minutes.

Attention and warmth produce real symptom change on their own, which is difficult to separate from any effect of the sound waves themselves. Separating those factors is precisely what stronger trial designs exist to do. Where passive pain relief is the goal, we more often reach for medical acupuncture, which our chiropractors and physiotherapists are trained to deliver as part of a broader plan.

Can Ultrasound Break Up Muscle Knots?

Ultrasound cannot break up muscle knots, because the waves do not mechanically tear or shear tissue at therapeutic settings. Therapeutic settings of 1 to 3 MHz at 1.0 watt per square centimetre produce heating and fluid agitation, and neither of those physically disrupts a taut band of muscle fibre.

Muscle fibre in a taut band responds to sustained pressure, stretch, and altered nerve input rather than to warmth alone. Warmth does help indirectly. Raising tissue temperature increases local circulation and reduces the resistance of connective tissue to stretch, which can make a subsequent hands-on technique more effective. Effectiveness of the hands-on technique, not the ultrasound, is what actually changes the knot.

Changing the knot is the work of direct manual pressure, and massage therapy is built around exactly that.

Direct pressure is what our registered massage therapists apply through trigger point work and techniques such as deep tissue massage. Techniques of that kind reach the taut band mechanically, in a way sound waves at these intensities never do.

Does Ultrasound Help Heal Tendons?

Ultrasound helps heal tendons inconsistently, and the published evidence for lower limb tendon conditions is limited. Shanks and colleagues, reviewing the literature in The Foot in 2010, found limited evidence for therapeutic ultrasound benefits across lower limb musculoskeletal conditions, a category that includes Achilles tendinopathy and plantar fascia problems.

Plantar fascia problems illustrate the difficulty well, since the tissue is dense, load-bearing, and slow to remodel. Slow-remodelling tissue responds to progressive mechanical loading, which is the intervention with the strongest evidence for tendinopathy across the board. Loading builds tendon capacity, while heating a tendon for ten minutes does not.

Building capacity is why our approach to conditions like plantar fasciitis centres on graded loading rather than passive heat. Passive heat can still play a supporting role in reducing symptoms enough for a patient to tolerate loading, and that supporting role is where therapeutic ultrasound has always been most defensible.

Does Ultrasound Therapy Really Work?

Ultrasound therapy works modestly for some conditions and the overall evidence base is weak. Weakness in the evidence is documented rather than speculative. Van der Windt and colleagues, publishing a systematic review of ultrasound therapy for musculoskeletal disorders in Pain in 1999, found limited benefits, and Shanks and colleagues reached the same conclusion for lower limb conditions eleven years later. StatPearls, summarising the position, states that more rigorous studies with clear indications and procedural techniques are needed before broad conclusions can be drawn about low-intensity ultrasound.

Broad conclusions being unavailable after ninety years of clinical use is itself informative. Informative findings of that kind have shifted clinical practice, and many physiotherapy clinics have reduced or dropped ultrasound in favour of modalities with stronger comparative data. Comparative data is where the contrast becomes clear, as the table below shows.

Feature	Therapeutic Ultrasound	Class IV Laser Therapy
Energy delivered	Mechanical sound waves	Light at specific wavelengths
Primary mechanism	Tissue heating and fluid agitation	Photobiomodulation of cell activity
Setting adjusted for depth	Frequency, 1 to 3 MHz	Wavelength and power output
Session length per area	3 to 10 minutes	5 to 15 minutes
Contact with skin	Required, through coupling gel	Handpiece moved over skin, no gel
Evidence level for musculoskeletal pain	Level III, systematic reviews report limited benefit	Randomised controlled trials favour laser in head-to-head comparisons
Main safety consideration	Superficial burns if the probe stops moving	Eye protection worn by patient and clinician
Recovery downtime	None	None

Sources: StatPearls, National Library of Medicine; van der Windt et al., Pain, 1999; Shanks et al., The Foot, 2010; Fiore et al., European Journal of Physical and Rehabilitation Medicine, 2011; Boyraz et al., BioMed Research International, 2015; Lasers in Medical Science, 2018.

Having set out what the evidence supports, the practical question becomes what to use instead. Instead of a passive modality with level III support, the strongest results in physiotherapy come from active care, which is why exercise rehabilitation forms the backbone of nearly every plan we build.

Who Should Not Have Ultrasound Therapy?

Ultrasound therapy is not suitable for everyone, and screening happens before any application. Screening covers both the treatment area and the patient’s wider medical history, since some exclusions relate to the tissue under the probe and others relate to conditions affecting the whole body.

Whole-body conditions and local tissue findings both appear on the standard exclusion list. StatPearls lists contraindications for ultrasound diathermy, and clinical practice adds several more:

• Bone fracture at or near the treatment site
• Malignancy, active or suspected
• Arteriosclerosis and ischemic tissue
• Active infection of tissue or bone
• Application over the eye or directly over the spine
• Hemophilia and other bleeding disorders
• Cardiac pacemakers and other implanted devices
• Cortisone injection at the site within the previous 30 days
• Open sores, lesions, burns, or active bleeding over the treatment area

Treatment areas are inspected visually before any modality is applied, which is standard across electrotherapy. Standard screening of this kind is carried out by our registered practitioners, each licensed through their provincial regulatory college, and it applies equally to laser, acupuncture, and any other modality we use.

What Should You Avoid After Ultrasound Therapy?

After ultrasound therapy you should avoid applying additional heat to the same area for several hours. Additional heat stacks on top of the temperature rise the treatment already produced, and stacked heat offers no extra benefit while raising the chance of skin irritation.

Skin irritation aside, there is no recovery downtime and no activity restriction beyond the sensible. Sensible limits mean returning to normal movement while holding back on aggressive stretching or heavy loading of a freshly warmed area for the rest of the day. Warmed connective tissue is temporarily more extensible, and pushing a stretch further than usual in that window can leave the tissue sore the following morning.

Soreness the following morning is worth reporting at the next appointment, since it tells the clinician the dose was too high for that tissue. Reporting it allows the settings or the follow-up exercises to be adjusted, which is how any modality gets calibrated to the individual patient rather than applied from a fixed template.

Why We Use Class IV K-Laser Instead of Ultrasound

We use Class IV K-Laser instead of ultrasound because head-to-head trials favour laser therapy over therapeutic ultrasound for musculoskeletal pain. Head-to-head comparisons exist across several conditions. Fiore and colleagues compared high-intensity laser therapy against ultrasound therapy for low back pain in a randomised controlled trial published in the European Journal of Physical and Rehabilitation Medicine in 2011, and Boyraz and colleagues ran a similar comparison in patients with lumbar discopathy, published in BioMed Research International in 2015.

Lumbar comparisons were followed by broader work reaching the same conclusion. A comparative study in Lasers in Medical Science in 2018 reported that laser photobiomodulation proved more effective than ultrasound therapy in patients with chronic non-specific low back pain. Low back pain is not the only region studied either. A randomised single-blind controlled trial of 60 office workers aged 25 to 55 with chronic neck pain found that photobiomodulation produced significantly greater improvement than conventional physiotherapy on both visual analogue and Neck Disability Index scores, at P less than 0.001.

Significance at that level is the kind of result the ultrasound literature has not produced. Producing stronger results also depends on using the right class of laser, and a 2025 systematic review with network meta-analysis found high-intensity laser therapy delivered a statistically superior analgesic effect compared with low-level cold laser, while noting the gains did not consistently exceed minimum clinically important difference thresholds. Thresholds aside, the direction of the evidence is why Class IV laser therapy is the light-based modality we invested in rather than a low-level unit.

A session with our unit follows a set sequence:

1. Clinical assessment to confirm whether laser is the right approach for your condition.
2. Eye protection fitted for both you and the practitioner as a standard precaution.
3. Targeted application of the handpiece over the specific tissue layers contributing to your pain, for 5 to 15 minutes per area.
4. Immediate return to activity, since there is no recovery downtime afterward.
5. Integration into your wider plan, combining laser with manual therapy and corrective exercise across the same appointment.
6. Review of progress, with most patients seeing meaningful improvement within four to ten sessions.

Improvement within that window depends heavily on what surrounds the laser. Surrounding care is where the real work happens, and laser at our Markham clinic is delivered by the same chiropractors and physiotherapists managing your whole plan rather than by a separate technician. Coordinated delivery of that kind pairs naturally with chiropractic care, manual therapy, and loading, which is how a passive modality earns its place.

Earning its place is the standard we hold every modality to. That standard is why our laser therapy is never sold as a course of treatment on its own, and why an assessment always comes before we recommend it.

Is This Kind of Therapy Covered by Insurance in Ontario?

Therapy of this kind is usually covered under your existing chiropractic or physiotherapy benefits rather than as a separate line item. Separate coverage for individual modalities is uncommon in Canadian extended health plans, which generally reimburse based on the practitioner delivering the care.

The practitioner delivering the care is therefore the determining factor. When a modality is applied by a registered chiropractor, it typically falls under chiropractic coverage, and when applied by a registered physiotherapist it typically falls under physiotherapy coverage. Coverage limits, annual maximums, and any referral requirements vary considerably between plans, so the only reliable answer comes from your own policy documents.

Policy documents also determine whether direct billing applies. At our Markham clinic we direct bill to most major insurance providers, and we verify your coverage at the first visit so there are no surprises at the front desk. Verification at the first visit takes a few minutes and saves the paperwork of claiming reimbursement yourself.

Frequently Asked Questions

What Is the Role of Ultrasound in Physiotherapy?

The role of ultrasound in physiotherapy is to prepare tissue and reduce symptoms so that active treatment becomes easier to tolerate. It warms deeper tissue, increases local circulation, and reduces connective tissue stiffness before hands-on work or exercise. Ultrasound is a supporting modality rather than a standalone treatment, and it has never been shown to replace manual therapy or progressive loading.

Do Physiotherapists Still Use Ultrasound Therapy?

Some physiotherapists still use ultrasound therapy, though its use has declined considerably as evidence for active treatment has strengthened. Physiotherapists have applied the modality since the 1930s, and it remains widely available. Many clinics have reduced or replaced it with modalities that perform better in direct comparison trials.

How Long Does It Take for Ultrasound Therapy to Work?

Ultrasound therapy produces its physical effects immediately, since tissue heating and increased blood flow happen during the session itself. Symptom change is slower and less predictable. The strongest available study recorded pain scores falling by roughly 4 points on a 0 to 10 scale over a course of treatment rather than after a single application.

How Many Times a Week Should You Have Ultrasound Therapy?

Ultrasound therapy is typically applied at the same frequency as your appointments, which for most rehabilitation plans means one to three times per week. No protocol has been established as superior, and this inconsistency across studies is one reason the evidence base is hard to interpret. Your clinician sets the frequency based on your condition and how you respond.

What Are the Side Effects of Ultrasound Therapy?

The main side effect of ultrasound therapy is superficial burning caused by prolonged exposure in one spot. Keeping the transducer in continuous motion throughout the session prevents it, which is why clinicians never rest the probe in place. Beyond that, complications are rare, and the modality is considered safe and non-invasive when applied correctly.

Is Ultrasound Therapy Outdated?

Ultrasound therapy is not outdated in the sense of being unsafe or unavailable, but its evidence base has not kept pace with the alternatives. Systematic reviews published in 1999 and 2010 both found limited benefit for musculoskeletal conditions, and the highest level of support recorded for low-intensity use remains level III. Newer light-based and loading-focused approaches now carry stronger comparative data.

Putting It All Together

Ultrasound in physiotherapy heats tissue and agitates the fluid within it, using sound waves at 1 to 3 MHz delivered through a gel-coupled probe for 3 to 10 minutes per area. Frequency selects the depth, tissue composition determines how much energy is absorbed, and the treatment is safe, painless, and free of downtime. What it does not do is break up muscle knots, rebuild tendon capacity, or produce the kind of results that systematic reviews have been able to confirm, with the highest level of support for musculoskeletal pain sitting at level III.

Level III support is why we made a different choice. Randomised trials comparing high-intensity laser against ultrasound have favoured laser across low back pain, lumbar discopathy, and chronic neck pain, so Class IV K-Laser is the light-based modality in our treatment rooms, always alongside manual therapy and progressive loading rather than in place of them. If a stubborn injury has plateaued and you want to know which modality actually fits your condition, an assessment at KC Rehab is a sensible starting point.

Starting points are meant to be easy. Give us a call at 905-205-1668 or book an assessment, and we will tell you honestly what will help and what will not.