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The International Society for Electrophysical Agents in Physical Therapy (ISEAPT) is a formal subgroup of the World Congress Physical Therapy (WCPT) and is the leading International organisation concerned primarily with Electro Physical Agents


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The Electro Physical Agents and Diagnostic Ultrasound (EPADU) group is a Professional Networks of the Chartered Society of Physiotherapy based in the UK.

Laser Therapy

Light Absorption in the Tissues
Laser - Tissue Interaction
Dose Calculations
Clinical Applications

[Low Intensity Laser Therapy – LILT : Low Level Laser Therapy – LLLT]

The term LASER is an acronym for the Light Amplification by Stimulated Emission of Radiation. In simple yet realistic terms, the laser can be considered to be a form of light amplifier - it provides enhancement of particular properties of light energy. 

Laser light will behave according to the basic laws of light, in that it travels in straight lines at a constant velocity in space. It can be transmitted, reflected, refracted and absorbed. It can be placed within the electromagnetic spectrum according to its wavelength/frequency which will vary according to the particular generator under consideration.

Visible Light Spectrum chart

There are several aspects of laser light which are deemed to be special and are often referred to in the literature. These include monochromacity, coherence and polarisation. There remains some doubt as to exactly how essential these particular aspects of laser light are in relation to the therapeutic application of this energy form. Monochromacity is probably the most important factor, as many of the therapeutic effects have been noted in various trials with light which is non-coherent. Additionally, it is thought that the polarisation is soon lost within the tissues & may therefore be less important than was thought at first.

Laser: white light/multiple wavelengths Laser: single wavelength Laser: LED light monochromatic
White Light
Multiple wavelenghts
Non coherent
Laser Light
Single wavelength
LED Light
Monochromatic but
Non coherent

Therapy Lasers have several common characteristics which are summarised below.

Terms: Therapy lasers tend to fall into a particular category of laser light known as 3A or 3B & are often referred to as 'soft laser' or 'mid laser' sources. More recently, the terms Low Level Laser Therapy (LLLT) and Low Intensity Laser Therapy (LILT) have been adopted. Ohshiro & Calderhead suggest that LLLT involves treatment with a dose that causes no detectable temperature rise in the treated tissues and no macroscopically visible change in tissue structure – essentially, the energy can cause in increase in temperature and a change in tissue structure, but that is not the intention with therapy laser which is applied at levels below that needed to achieve these more overt effects (c/f surgical laser). 

Parameters: Most LLLT apparatus generates light in the Red Visible & Near Infra-red bands of the EM spectrum, with typical wavelengths of 600 -1000nm. The mean power of such devices is generally low (1-100mW), though the peak power may be much higher than this.

The treatment device may be a single emitter or a cluster of several emitters, though it is common for most emitters in a cluster to be non laser type devices. The beam from single probes is usually narrow (Æ1mm-6 or 7mm) at the source. A cluster probe will usually incorporate both higher and lower power emitters of different wavelengths.

Examples of LILT Probes

The output may be continuous or pulsed, with narrow pulse widths (in the nano or micro second ranges) and a wide variety of pulse repetition rates from 2Hz up to several thousand Hz. It is difficult to identify the evidence for the use of pulsing from the research literature, though it would appear to be a general trend that the lower puling rates are more effective in the acute conditions whilst higher pulse rates work better in more chronic conditions. There is a growing body of support that suggests that the pulsing settings are of secondary importance in terms of clinical doses.

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Light Absorption in the Tissues

As with any form of energy used in electrotherapy, the energy must be absorbed by the tissues in order to have some effect. If exactly the same amount of energy left the tissues which was introduced into them, it is difficult to rationalise what kind of effect might have been achieved. The absorption of light energy within the tissues is a complex issue, but generally, the shorter wavelengths (ultraviolet & shorter visible) are primarily absorbed in the epidermis by the pigments, amino & nucleic acids. The longer IRR wavelengths (>1300nm) appear to be rapidly absorbed by water & therefore have a limited penetration into the tissues. The band between (i.e. 600-1000nm) are capable of penetration beyond the very superficial epidermis & are, in part at least, available for absorption by other biological tissues.

LLLT when applied to the body tissues, delivers energy at a level sufficient to disturb local electron orbits & result in the generation of heat, initiate chemical change, disrupt molecular bonds & produce free radicals. These are considered to be the primary mechanisms by which LLLT achieves its physiological & therefore therapeutic effects and the primary target is effectively the cell membrane (see below).

Although much of the applied laser light is absorbed in the superficial tissues, it is proposed that deeper or more distant effects can be achieved, probably as a secondary consequence via some chemical mediator or second messenger systems, though there is limited evidence to fully support this contention.

The actual penetration of LLLT at common wavelengths is a widely debated point & it is common to find widely varying values cited in the literature. It is often claimed that because laser light is monochromatic, polarised & coherent it is capable of greater penetration than 'normal' (or non-coherent) light. This should give penetration depths of 3-7mm for visible red light & some 30-40mm for IRR laser light though 10-15mm is probably a more realistic penetration in human tissue.

The fact that the polarisation appears to be lost in the tissues, as is much, if not all of the coherence, will result in a shallower penetration. King cites a more realistic penetration depth for 630nm light to be 1-2mm, whilst at 800-900nm one could expect penetration depths of 2-4mm. (Penetration depth in this context refers to the depth of the tissues to which 37% of the light at the surface is able to penetrate). A very small % of the light energy available at the surface will be available at 10mm or more into the tissues.

Laser - Tissue Interaction

As with many other forms of energy delivered to the patient under the umbrella of electrotherapy, the primary effects are divided into thermal and non thermal. LLLT is generally considered to be a non thermal energy application, though one must be careful to appreciate that delivery and absorption of any energy to the body will result in the development of heat to some extent. Non thermal in this context really relates to the non accumulative nature of the thermal energy.

Photobioactivation is a commonly used phrase in connection with LILT - meaning the stimulation of various biological events using light energy but without significant temperature changes. Much, if not all the cited work on therapeutic laser consider these photobioactivation effects. Some authors have proposed that there are other terms which are preferable to photobioactivation including photobiostimulation and photobiomodulation. It provides for a great semantic argument, but assume at this point that therms are generally interchangeable.

Many of the early ideas of photobioactivation were proposed by Karu who reported & demonstrated several key factors. She notes in her 1987 paper that some biomolecules (DNA, RNA) change their activity in response to irradiation with low intensity visible light, but that these molecules do not appear to absorb the light directly. The cell membrane appears to be the primary absorber of the energy which then generates intracellular effects by means of a second messenger / cascade type response. The magnitude of the photoresponse was deemed to be determined at least in part by the state of the cells/tissues prior to irradiation, summarised in a simple statement that 'starving cells are more photosensitive than well fed ones'. The laser light irradiation of the tissues is seen then as a trigger for the alteration of cell metabolic processes, via a process of photosignal transduction. The often cited Arndt-Schults Law supports this proposal.

The list of cellular & more general physiological effects is extensive, but it must be considered realistically in that much of the work relates to in vitro experimentation with no direct proof that the results are directly related to living mammalian tissues in vivo.

The following list of physiological & cellular level effects is compiled from several reviews & research papers & does not claim to be complete or guaranteed for the in vivo situation. It does however illustrate the range & scope of photobioactivation effects.   

  • Altered cell proliferation
  • Altered cell motility
  • Activation of phagocytes
  • Stimulation of immune responses
  • Increased cellular metabolism
  • Stimulation of macrophages
  • Stimulation of mast cell degranulation
  • Activation & proliferation of fibroblasts
  • Alteration of cell membrane potentials
  • Stimulation of angiogenesis
  • Alteration of action potentials
  • Altered prostaglandin production
  • Altered endogenous opoid production 

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Dose Calculations 

Most research groups and many manufacturers, recommend that the dose delivered to a patient during a treatment session should be based on the ENERGY DENSITY rather than the power or other measure of dose. Energy Density is measured in units of Joules per square centimetre (J/cm2). One of the most significant inhibitors to the more widespread adoption of laser therapy in the clinical environment relates to the difficulty in getting these ‘effective’ laser doses to work on a particular machine. Few devices enable the practitioner to set the dose in J/cm2. Some will provide Joules, some Watts, some watts/cm-2 etc etc. It is currently argued that Joules (i.e. Energy) may in fact be the most critical parameter rather than Energy Density. The debate is not yet resolved, and the energy density will be used here, mainly because the published research almost exclusively cites it, and therefore, it may be of more use when it comes to trying to replicate an evidence based treatment dose.

Some machines offer 'on board' calculations of this dose, whilst other machines require the operator to make some simple calculations based on several considerations:

  • output power (Watts)
  • irradiation area (cm2)
  • time (seconds)
  • If PULSED - pulse width, frequency and power settings

ENERGY DENSITY (J/cm2) = Total amount of energy (J) / Irradiation area (cm2)

TOTAL ENERGY (J) = Average Power (Watts) x Time (sec)

AVERAGE POWER (Watts) = Peak power (W) x Frequency (Hz) x Pulse Duration (sec) (PULSED OUTPUT ONLY)                                               

There are various alternative methods for calculating these doses, but those cited above offer a reasonably simple method should one be needed.

Most authorities suggest that the ENERGY DENSITY per TREATMENT SESSION should generally fall in the range of 0.1 - 12.0 J/cm2 though there are some recommendations which go up to 30 J/cm2. It has been previously suggested that a maximal (single treatment) dose of 4 J/cm2 should not be exceeded. The evidence would not support that contention. Again as a generality, lower doses should be applied to the more acute lesions which would appear to be more energy sensitive.

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Clinical Applications

The recent research, both laboratory based & clinical trials, is found to concentrate on a few key areas. Most dominant amongst these are wound healing, inflammatory arthropathies, soft tissue injury and the relief of pain. There is supportive research for the clinical use of LLLT in these and other circumstances, but, as with many treatment modalities, the evidence remains somewhat controversial at the present time.

Open Wounds

There is a growing body of evidence in this context, with some mixed results, but on the whole, they are positive outcome trials. There`are useful chapters/sections in the Baxter text and more recently in the Tuner and Hode book. A general summary\might conclude that a treatment programme could be thus :

Treat to the floor of the ulcer / pressure sore / wound
Often use cluster probe to cover the area
Typically up to 2 J/cm2
Also treat margin/periphery
Often use single probe
Typically up to 4 J/cm2 

Inflammatory Arthropathies

There have been several trials involving the use of LILT and various inflammatory problems in joints. As with the wound work, there are mixed results, but the general trend appears to be largely supportive. The recent Ottawa Panel review was supportive of laser therapy in RA.

Soft Tissue Injury

There is a fairly widespread use of LILT in a variety of soft tissue treatments. Some results are excellent and others poor. It is possible that the weak results relate to incorrect doses or possibly considering the use of laser therapy for injuries that are simply beyond the reach of the energy delivered (see penetration section above). The Tuner and Hode book has multiple examples of effective (and less effective) soft tissue treatments with LILT and identifies some of the key research in this area.


It was broadly assumed (until more recently) that the effect of laser therapy with regards to pain relief was primarily a secondary effect of dealing with the inflammatory state. Whilst this may well be true (to some extent at least), there is growing evidence that laser therapy can have a more direct effect of nerve conduction characteristics and hence may result in reduced pain as a more direct effect of the therapy. A recent example of a paper along these lines would be Vinck et al 2005.

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Essential References

(2004). "Ottawa panel evidence-based clinical practice guidelines for electrotherapy and thermotherapy interventions in the management of rheumatoid arthritis in adults."  84(11): 1016-1043.

Baxter, D (1993) Therapeutic Lasers, Pub : Churchill Livingstone

Baxter, D. (2008) Low Intensity Laser Therapy. Chapter 11 in : Electrotherapy : Evidence Based Practice. Editor : T Watson. Elsevier.

Kitchen, S Partridge, C. (1991) A Review of Low Level Laser Therapy. Physiotherapy 77(161-168)

King, P. (1990)  Low-level laser therapy: A Review. Physiotherapy Theory & Practice 6(127-138)

Karu, T. (1987) Photobiological fundamentals of low power laser therapy. IEEE Journal of Quantum Electronics QE23(10);1703-1717

Ohshiro, T. Calderhead, R. (1988) Low Level Laser Therapy. Pub.John Wiley & SonsTuner, J. and L. Hode (2002). Laser Therapy: Clinical Practice & Scientific Background. Grangesberg, Sweden, Prima Books AB.

Tuner, J. and L. Hode (2004). The Laser Therapy Handbook. Prima Books AB

Vinck, E. et al. (2005). "Evidence of changes in sural nerve conduction mediated by light emitting diode irradiation." Lasers Med Sci 20(1): 35-40.

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A wide range of Electrotherapy Courses are delivered throughout the UK, Europe and Worldwide with varying content, aims and duration.



Current books on Electrotherapy with brief descriptions and links to Amazon pages for purchase.

FAQs: Prof. Tim Watson

FAQs: Prof. Tim Watson

Some common answers to the most frequently asked questions on Electrotherapy, particularly in the area of Contraindications.