Low Level Laser Therapy (LLLT): What it is, how it is applied and an overview of the research.

Summary

This lecture covers the principles and applications of low-level laser therapy (LLLT), an electro-therapeutic modality that uses lasers to relieve pain and stimulate cell function. The lecture explains how lasers work, emphasizing key properties such as monochromaticity, coherence, and collimation. It also describes how factors like wavelength, power, and fluence influence tissue interaction. Despite its growing use in treating musculoskeletal conditions, evidence for LLLT’s effectiveness remains inconsistent, with conflicting research results across various conditions, including tendinopathy, neck pain, and low back pain. Ongoing research aims to clarify its therapeutic potential.

Takeaways

• 🔬 Lasers produce light through stimulated emission of radiation, and are characterized by coherent, monochromatic light with minimal divergence.
• 💡 Low-level laser therapy (LLLT) is used in physiotherapy to relieve pain and enhance cell function, though its mechanisms and effectiveness are still under research.
• 📜 LLLT is theorized to follow the Grotthus-Draper law, where light must be absorbed to trigger photochemical reactions, potentially boosting ATP production through enzymes like cytochrome C oxidase.
• ⚡ The unique properties of lasers include monochromaticity (same wavelength), coherence (synchronized photons), and collimation (nearly parallel beams).
• 📏 Various factors influence laser interactions with tissues, including wavelength, power, pulse rate, and spot size, all of which affect penetration and energy absorption.
• 📊 LLLT parameters such as energy density, power output, and pulse rate are adjustable, and machines used in therapy typically operate in the 600-1000 nm wavelength range for deeper tissue penetration.
• 🧪 Evidence on the effectiveness of LLLT is mixed, with studies on conditions like tendinopathy and low back pain showing inconsistent results.
• 🧠 Placebo effects may play a role in LLLT’s perceived benefits, emphasizing the need for high-quality randomized controlled trials in research.
• 📝 Systematic reviews on LLLT for conditions such as rheumatoid arthritis, osteoarthritis, and frozen shoulder show conflicting results, often due to study bias or varying methodologies.
• 🧑‍⚕️ LLLT treatment protocols differ by condition, with recommendations such as 8 joules per square centimeter for Achilles tendinopathy, though treatment effectiveness can vary significantly.

Q & A

What is a laser and how does it function?

A laser is a device that amplifies light through stimulated emission of radiation to produce a coherent, monochromatic beam. It consists of an energy source, a resonant chamber, and an active medium. Electrons in the active medium are excited and emit photons when they return to their ground state. These photons reflect between mirrors in the chamber and exit as a focused beam directed at a target tissue.

What are the unique properties of laser light compared to conventional light?

Laser light has three unique properties: monochromaticity (all photons have the same wavelength), coherence (photons are synchronized in time and space), and collimation (laser beams are nearly parallel and can be focused to a small area with little divergence).

How does low-level laser therapy (LLLT) theoretically work?

LLLT works on the principle of the Grotthus Draper law, which states that light must be absorbed by a chemical substance for a photochemical reaction to occur. LLLT is believed to stimulate cellular processes like oxidative phosphorylation and the production of ATP by affecting enzymes such as cytochrome C oxidase in mitochondria.

What are some of the factors that influence how a laser interacts with tissue?

Several factors influence laser-tissue interaction: the wavelength of the laser, the power and power density, pulse duration, spot size, fluence (energy density), properties of the target tissue, and the duration of exposure. Longer wavelengths penetrate deeper into tissues, and energy density affects the intensity of the treatment.

How is energy density calculated in laser therapy?

Energy density (fluence) is calculated by dividing the total energy (in joules) by the area of application (in square centimeters). The energy itself is determined by multiplying the power (in watts) by the treatment time.

What is the role of pulse duration in low-level laser therapy?

Pulse duration (or pulse rate) is crucial for determining how the laser energy is delivered. For more acute and superficial injuries, lower pulse rates are used, while chronic conditions typically require higher pulse rates. The pulse duration is related to the thermal relaxation time, which is the time it takes for tissue to return to its baseline temperature after being heated.

What evidence exists for the effectiveness of low-level laser therapy?

The evidence for LLLT's effectiveness is mixed and often of variable quality. Some studies show benefits for conditions like tendinopathy and low back pain, while others find no significant effects. Systematic reviews often highlight inconsistencies and methodological flaws in existing research.

What are some of the common applications of low-level laser therapy?

LLLT is commonly applied to treat musculoskeletal conditions, such as tendinopathies, low back pain, neck pain, and frozen shoulder. However, the efficacy of treatment varies depending on the condition and the parameters used in the therapy.

How do the wavelength and spot size affect tissue penetration in laser therapy?

Wavelength determines the depth of tissue penetration; longer wavelengths penetrate more deeply. Spot size also affects energy delivery, with larger spot sizes leading to less scattering and deeper penetration compared to smaller spot sizes.

What are the primary challenges in conducting research on low-level laser therapy?

Challenges in LLLT research include variability in treatment protocols (wavelength, power, duration), difficulty controlling for the placebo effect, and the lack of high-quality randomized control trials. Many studies also suffer from low quality, small sample sizes, and inconsistent results.

Outlines

00:00

🔬 Understanding Laser Devices and Their Mechanisms

This paragraph explains the fundamental workings of lasers, focusing on their use in both medical and therapeutic settings. It introduces the concept of low-level laser therapy (LLLT), describing how lasers stimulate chemical reactions within cells. The theory behind LLLT is based on the Grotthus Draper law of photochemistry, which states that light must be absorbed by a substance to cause a reaction. The paragraph also discusses how LLLT may influence processes such as ATP production and mitochondrial function to benefit tissue healing, though ongoing research is still determining its full therapeutic potential.

05:01

💡 Production, Properties, and Application of Lasers

The second paragraph delves deeper into how lasers function, focusing on the components like the resonant chamber, active medium, and mirrors that generate laser beams. It outlines the properties of lasers—monochromaticity, coherence, and collimation—that make them unique compared to conventional light sources. It also discusses how laser beams interact with tissue, explaining the factors such as wavelength, power, and fluence that influence their effectiveness and tissue penetration. The paragraph concludes with an overview of how pulse duration and spot size impact the thermal effects of laser energy on tissues.

10:06

🔍 Parameters and Application of Low-Level Laser Therapy

This paragraph discusses the practical aspects of applying low-level laser therapy (LLLT), including the importance of various parameters like energy density, power, and spot size. It explains how energy is delivered to tissue, with smaller spot sizes leading to greater scattering, and highlights the importance of energy density and power for determining treatment effectiveness. The paragraph also walks through an example calculation for determining treatment time for Achilles tendinopathy using laser therapy, explaining how to adjust pulse rates for acute versus chronic injuries.

📊 Evidence and Research on Low-Level Laser Therapy

The fourth paragraph focuses on the research surrounding low-level laser therapy (LLLT), noting that evidence for its effectiveness is mixed and often inconclusive. It presents findings from systematic reviews and clinical trials that have investigated LLLT for conditions like tendinopathy, low back pain, and rheumatoid arthritis. The paragraph points out that while some studies suggest benefits, many others show no significant effect or are deemed to be of low quality due to biases and inconsistent methodologies. The paragraph concludes by acknowledging the ongoing debate about LLLT’s efficacy and the need for more rigorous research.

🧪 Summary of Research on Low-Level Laser Therapy

This paragraph continues the discussion on the evidence supporting low-level laser therapy, summarizing the results of various systematic reviews and studies. It highlights inconsistent and conflicting results across research, especially in studies of neck pain, rheumatoid arthritis, osteoarthritis, and frozen shoulder. The paragraph stresses that many of the studies suffer from a high risk of bias and low-quality evidence, although some positive results have been observed. It ends by reiterating the need for better-quality research to clarify the true effectiveness of LLLT in clinical settings.

Keywords

💡Low-Level Laser Therapy (LLLT)

Low-Level Laser Therapy refers to the use of low-power lasers to relieve pain and enhance cell function through phototherapy. It is theorized to work by impacting chemical reactions in cells, such as oxidative phosphorylation, to produce therapeutic effects. The video discusses its application in physiotherapy to treat musculoskeletal conditions, though its clinical effectiveness remains debated.

💡Grotthus-Draper Law

The Grotthus-Draper Law is a principle in photochemistry that states light must be absorbed by a substance to trigger a photochemical reaction. This law is essential to understanding how LLLT works, as the laser light needs to be absorbed by chromophores in the body to produce therapeutic effects like increased ATP production in cells.

💡Chromophores

Chromophores are biomolecules that can absorb photons from laser light. In the context of LLLT, these molecules are critical because they trigger the biological effects that lead to pain relief and enhanced cell function when exposed to specific wavelengths of light. Their ability to absorb energy ties directly into the Grotthus-Draper Law, as mentioned in the video.

💡Monochromaticity

Monochromaticity is the property of laser light that ensures all emitted photons are of the same wavelength. This is a unique characteristic of lasers that distinguishes them from other light sources, which emit multiple wavelengths. In LLLT, this property is crucial for targeting specific tissues and ensuring that the laser light penetrates deeply and consistently.

💡Coherence

Coherence refers to the synchronization of the photons in the laser beam, meaning they are in phase and travel uniformly. This property is important for the precision of LLLT, as it allows the laser to focus on a small area and deliver energy consistently. The video contrasts laser coherence with the random travel of photons in conventional light.

💡Collimation

Collimation describes the near-parallel nature of the laser beam, meaning it spreads very little as it travels. This allows lasers to focus energy on a small target area, which is especially useful in medical applications like LLLT, where precision is needed to deliver therapeutic doses to specific tissues without affecting surrounding areas.

💡Fluence

Fluence, or energy density, is a measure of energy delivered per unit area, typically expressed in joules per square centimeter. In LLLT, fluence determines the amount of energy delivered to the tissue, which is key for achieving the desired therapeutic effect. Higher fluence is used for tissue destruction, while lower fluence, under 35 J/cm², is used in LLLT.

💡Pulse Duration

Pulse duration, also known as pulse rate or pulse frequency, refers to the length of time the laser beam is emitted. In LLLT, different pulse durations are used depending on the condition being treated. For instance, low pulse rates are used for acute injuries, while higher rates are employed for chronic conditions, such as tendinopathy.

💡Thermal Relaxation Time

Thermal relaxation time is the time it takes for tissue to return to its baseline temperature after being heated by the laser. In LLLT, it helps determine the appropriate pulse duration. If a tissue is heated for less than its thermal relaxation time, heat remains confined to the target area, improving the treatment's precision and effectiveness.

💡Clinical Evidence

Clinical evidence refers to the body of research and trials that assess the effectiveness of treatments like LLLT. The video emphasizes that despite some positive findings, the evidence for LLLT is inconsistent and often of low quality. Many studies suffer from variability in treatment protocols, and randomized control trials are rare, leading to ongoing debate about its true efficacy.

Highlights

Lasers rely on stimulated emission of radiation to produce coherent wavelengths in the ultraviolet, visible, or infrared spectrum.

High-power lasers are used in laser medicine to cut or destroy tissue, while low-power lasers are used in physiotherapy for pain relief and enhancing cell function through phototherapy.

Low-level laser therapy is based on the Grotthus Draper law, which states that light must be absorbed by a chemical substance for a photochemical reaction to occur.

The theory suggests that low-level laser therapy can impact chemical reactions like oxidative phosphorylation, potentially increasing ATP production and respiratory enzymes such as cytochrome C oxidase.

Lasers have unique properties such as monochromaticity, coherence, and collimation, which differentiate them from other electromagnetic radiation forms.

Monochromaticity means all photons in the laser beam are of the same wavelength, while coherence refers to the synchronization of photons in time and space.

Collimation ensures that laser beams are nearly parallel, allowing the energy to be focused on a small area without substantial divergence.

The interaction of laser energy with tissues depends on variables like wavelength, power, spot size, energy density, and tissue exposure duration.

Longer laser wavelengths penetrate tissue more deeply, and the pulse duration is tied to the thermal relaxation time of the target tissue.

The spot size affects energy delivery, with smaller spot sizes causing more scattering, while larger ones enable deeper penetration.

Power density, measured in watts per square centimeter, affects how quickly tissue heats, determining whether the effect is coagulation or vaporization.

For low-level laser therapy, the optimal energy density is generally below 35 joules per square centimeter, depending on the condition treated.

Inconsistent research evidence regarding the effectiveness of low-level laser therapy, particularly in conditions like tendinopathy and low back pain, suggests mixed results.

Placebo effects and variable parameters across studies complicate the evaluation of laser therapy's clinical effectiveness.

Systematic reviews and meta-analyses show conflicting outcomes, with studies on conditions like tendinopathy, back pain, and rheumatoid arthritis offering inconclusive evidence.

Research continues, and while some low-quality trials suggest potential benefits, high-quality randomized control trials are rare, making definitive conclusions challenging.

Transcripts

Lasers are devices that rely upon the stimulated  emission of radiation to produce a single,  

coherent wavelength within the ultraviolet,  visible or infrared portion of the electromagnetic  

spectrum. Whereas high power lasers are used  in laser medicine to cut or destroy tissue,  

physiotherapists use low power lasers  to relieve pain and stimulate or enhance  

cell function through phototherapy  (or so the theory goes). Briefly,  

low-level laser therapy is theorised to work on  the basis of the first law in photochemistry:  

the Grotthus Draper law, which states that  light must be absorbed by a chemical substance  

in order for a photochemical reaction to take  place. The generally accepted theory is that  

low-level laser therapy can impact chemical  reactions (like oxidative phosphorylation)  

and therefore the production of ATP or  chemical substances like the respiratory enzyme  

cytochrome C oxidase (which is involved in  the electron transport chain in mitochondria),  

for therapeutic benefit. Research is ongoing  about these therapeutic mechanisms but its  

effects appear to be limited to a specified set  of wavelengths and parameters. In this lecture,  

we will review the basic principles of  low-level laser therapy: how it is produced,  

applied and its evidence for treating a number  of different musculoskeletal conditions.  

Lasers are devices that rely upon the stimulated  emission of radiation to produce a beam of light.  

The word 'laser' is an acronym for 'Light  Amplification by Stimulated Emission of  

Radiation'. Lasers are comprised of  an energy source, a resonant chamber  

and an active medium. Let's start with the  resonant chamber, which contains the active  

laser medium and several reflective mirrors. When  they are in an unexcited state the electrons of  

the atoms in the active medium orbit their nucleus  at their lowest energy level or 'ground state',  

and these orbits are closer to the nucleus. But  when an external energy source is applied to  

the resonant chamber, this excites the electrons  in the active medium and moves them to a higher  

orbit. As the electrons return from the  excited state back to the ground state,  

they spontaneously emit photons of energy  in the form of electromagnetic radiation.  

These photons reflect back and forth  between the mirrors of the resonant chamber,  

some of which reflect all of the photons and  others which reflect only some of them, and then  

they ultimately exit the device where they are  directed to a target tissue. These target tissues  

contain 'chromophores' or biomolecules which are  capable of being excited by the incoming photons.  

The way lasers are produced means  that they have some unique properties,  

when compared to other forms of electromagnetic  radiation, and these include monochromaticity,  

coherence and collimation. 'Monochromatic'  means that all the photons in a laser beam  

are of the same wavelength. 'Coherence' refers  to the synchronisation of a laser beam in time  

and space where the photons of the beam are in  phase and coherent. By comparison the photons  

in conventional light travel randomly.  'Collimation' means that the elements of  

the laser beam are nearly parallel because there  is little divergence. Laser beams can be focused  

to a small area. Again, this property differs from  conventional light (which diverges substantially).

When laser energy strikes the tissue surface that  energy can be absorbed, reflected, transmitted  

elsewhere or scattered. The kind of interaction  that happens depends upon a number of variables,  

including the active medium (which determines the  wavelength of the laser), the power, the power  

density of the laser, its pulse duration, the  spot size used, the fluence (or energy density)  

of the laser, the properties of the target  tissue and the duration of tissue exposure.  

The wavelength of the laser beam determines  the degree of tissue penetration, the amount  

of energy that is absorbed and the amount that  is scattered. Basically, longer wavelengths  

penetrate more deeply. The pulse duration, also  known as the pulse frequency or pulse rate, is  

determined from the thermal relaxation time of the  target chromophore. The thermal relaxation time  

is the time needed for the tissue temperature to  return to its baseline temperature after heating.  

For example, if a tissue is heated for a period  less than or equal to its thermal relaxation time,  

the accumulated heat is confined to the target  object whereas if a target is heated for longer  

than its thermal relaxation time, conduction  leads to heating of surrounding structures.  

The spot size is the diameter of the beam emitted  from the laser as it strikes the tissue surface.  

Energy entering the target tissue is attenuated  more rapidly with the small spot size compared  

with the larger spot size because scattering is  greater with a small spot size. The spot size is  

usually determined by the equipment you are using.  For example, the spot sizes of the equipment we  

will be using in our practical classes ranges from  0.13 to 0.28 centimetres-squared. Next, the amount  

of energy that is delivered. Energy is measured  in joules and 'fluence' (or energy density)  

is energy divided by the application area, so  its units are in joules per square centimetre.  

When it comes to medical lasers, the destruction  of large tissues or structures requires high  

fluence due to the amount of tissue that needs  to be heated to achieve thermal coagulation.  

But for low-level laser therapy, the fluence is  generally below 35 joules per square centimetre.  

'Power' describes the rate of energy delivery and  is measured in joules per second or 'watts'. Power  

density-the power transmitted per unit area of  cross section of a laser beam (which is measured  

in watts per square centimetre)-is inversely  proportional to the square of the diameter of  

the spot size. In other words, energy applied over  a small surface area means higher power densities  

compared with the same amount of energy  applied over a larger surface area.  

Lower power density produces slow  heating that coagulates tissue,  

while high power density heats tissue  quickly and can vaporise tissue.

So they are the various parameters, but how is  low-level laser therapy actually applied? Well,  

a lot comes down to the type of machine that you  have. For example, I had mentioned before how the  

wavelength of the laser (and therefore the depth  of penetration) is determined by the active laser  

medium of the machine. So for this parameter,  the machines that we have here are capable of  

producing lasers with wavelengths of between  600-1000 nanometers, which is associated with  

the depth of penetration below the level of the  dermis into the underlying subcutaneous tissue.  

Their spot sizes range from 0.1-0.3  centimetres-squared, and their power outputs are  

between 65 and 200 milliwatts. So really, the only  parameters we're going to have any control over  

are the pulse rate and the treatment time. When  calculating the desired energy density, the World  

Association of Laser Therapy have guidelines for a  variety of different conditions. So for instance,  

they recommend delivery of an energy density  of 8 joules per centimetre squared for treating  

achilles tendinopathy. As I said before, energy  density is the energy divided by the spot size,  

and energy is equal to power multiplied by time.  So we have the target energy density (8 joules  

per square centimetre), we have the power of the  machine (let's say 0.2 watts), and we have the  

spot size (which is 0.25 centimetres-squared).  So the last remaining unknown-treatment time-is  

the energy density, multiplied by the spot size,  divided by the power, or '8' multiplied by '0.125'  

divided by '0.2', which gives us a 5-second  treatment time. For the area we are treating,  

the last parameter-the pulse duration-can  be controlled on the machine.  

Generally, for more acute and superficial injuries  low pulse rates are used, while higher pulse  

rates are preferred for chronic conditions.  Taking the example of achilles tendinopathy,  

which would be considered a chronic condition,  a pulse duration of 5 kilohertz might be used.  

Treatment might be performed daily for 2 weeks, or  every other day for 3-4 weeks. Contraindications  

according to the North American Association  for Laser Therapy are presented on screen.  

But does laser are actually work, what's the  evidence? Like other electrophysical modalities,  

the evidence for the effectiveness of laser is  conflicting, of variable quality and depends on  

the population being studied. The World  Association of Laser Therapy (or WALT)  

recently published recommendations for the design  and conduct of clinical studies of low-level laser  

therapy, but currently available evidence rarely  follows all of these recommendations. You see,  

performing research on electrophysical modalities  is complicated because patients expectations  

probably have an important role in the benefit  that comes from a treatment, so the placebo effect  

is often at play. That's why high quality,  randomised control trials where the patients  

and therapists are blinded to group allocation  are so important in this field, but they are rare.  

Convincing evidence for the efficacy of low-level  laser therapy in patients with tendinopathy is  

lacking; a systematic review and meta-analysis of  controlled clinical trials reported inconsistent  

results with 12 studies showing some benefit while  13 reported inconclusive results or no effect.  

The authors noted that, like much of the research  investigating other electrophysical modalities,  

studies varied in quality and  in the doses or parameters used.  

A 2005 systematic review of studies of low-level  laser therapy for patients with lateral epicondyle  

tendinopathy concluded that there was no  clinically significant effect, either in  

the short- or long-term compared with placebo. And  several controlled trials in which patients were  

randomly assigned to treatment with low-level  laser therapy or placebo laser reported that  

active laser treatment did not improve outcomes  beyond those achieved with eccentric exercise.  

For patients with low back pain,  results again are largely inconsistent.  

For example, four trials found laser therapy to  be superior to sham therapy for pain relief and  

improvement in function up to one  year following treatment. However,  

two other trials failed to show a benefit of laser  therapy when used either alone or with exercise.  

Findings from a 2008 Cochrane review found  that the evidence was inconclusive for the  

use of low-level laser therapy in the  treatment of non-specific low back pain,  

with the authors noting that protocols varied  widely with lots of different treatment doses,  

durations and wavelengths used. And these  findings were echoed in two other systematic  

reviews published in 2010 and 2015. And there's  lots of other research which has been done in  

other patient populations. I can't go into too  much detail (because it would take too long),  

but I'll give you a brief summary of  some of the better systematic reviews,  

one review concluded that low-level laser  therapy may be useful in the treatment of  

both acute and chronic neck pain, but then  another more recent review with meta-analysis  

concluded that the benefits were insignificant  and that the evidence had a high risk of bias,  

which is just another way of saying the  available studies were low in quality.  

A Cochrane review published in 2005 found  that low-level laser therapy may be useful for  

short-term pain relief in patients with rheumatoid  arthritis, but again the studies that were  

included were deemed to be at a high risk of bias.  For osteoarthritis, another Cochrane review found  

results to be conflicting, making it difficult  to draw any conclusions. And another Cochrane  

review published in 2014 investigating a range of  electrotherapeutic modalities for frozen shoulder  

found that there might be some benefit for  laser, but this was based on one, low-quality  

trial. And I could go on, but the findings are  largely the same: inconsistent and conflicting  

with lots of low quality, heterogeneous studies,  but new evidence may emerge to change this. So  

that concludes this lecture on low-level laser  therapy. To recap, I started by outlining what  

lasers are and how low-level laser therapy  is used as an electro-therapeutic modality.  

I outlined the theory of how it might  work and the various treatment parameters.  

I finished by discussing some of the research  investigating its clinical effectiveness.