Laser and Photobiomodulation

The proposed mechanism is absorption of photons by chromophores within the cell, with cytochrome c oxidase in the mitochondrial respiratory chain the leading proposed chromophore rather than a definitively established one, which is thought to increase adenosine triphosphate production, modulate reactive oxygen species and influence downstream signalling, with secondary effects on inflammatory mediators and on nerve conduction that may explain analgesia. Near-infrared wavelengths generally penetrate more deeply than visible red light, which is why deeper targets such as tendon are usually treated with near-infrared devices, but actual exposure at the target also depends on power, beam characteristics, skin, tissue depth and device technique. Melanin and haemoglobin absorb strongly and reduce penetration, so skin pigmentation and overlying tissue depth both matter.

Dose is where most of the difficulty lies. It is described by wavelength, power output and treatment time, with fluence conventionally expressed in joules per square centimetre; importantly this usually describes the energy density at the treatment surface rather than the dose actually reaching a deep tendon, which is not directly known. The dose response is proposed to be biphasic, so that too little energy produces no effect and too much may inhibit rather than stimulate, which is biologically plausible but translates uncertainly into clinical dosing. Consensus dose recommendations exist, notably those published by the World Association for Photobiomodulation Therapy, which specify wavelength and energy by anatomical site for chronic arthritic and inflammatory conditions; these are professional consensus guidance rather than UK national guidance. In practice contact and non-contact techniques both exist depending on the device, the treated area should be clean, and the power output should be verified periodically, since output drifts and an uncalibrated device may deliver far less than the display suggests.

The evidence is mixed rather than uniformly negative, which distinguishes photobiomodulation from some other device therapies, but benefit statements should be kept condition-specific rather than pooled into a single claim. An umbrella review of randomised trials concluded that possible benefits exist for selected outcomes, but that certainty is mainly low or very low, with only some outcomes reaching moderate certainty, and that protocol standardisation remains inadequate. In UK guidance terms, laser therapy is advised against for osteoarthritis because of insufficient evidence of benefit, and for chronic primary pain no clinical recommendation was made because the evidence and cost-effectiveness were too uncertain, which is not the same as endorsement. The most important methodological criticism is that trials frequently report insufficient detail about wavelength, power and delivered energy to allow the dose to be evaluated, so negative studies cannot be distinguished from studies that never delivered an adequate dose to the target. A clinician who can articulate that point is doing better than one who simply asserts that laser does or does not work.

Safety is good, which is part of why it is widely used, but two issues need explicit attention. Eye protection must be appropriate to the wavelength, device type and laser class, because even low-power laser can cause retinal injury if the beam enters the eye directly; laser devices require suitable eye protection and controlled access, while light-emitting diode systems need a device-specific optical risk assessment. Beyond that, manufacturer and local laser-safety guidance should be followed, and common precautions include direct ocular exposure, known malignancy in the treatment field, active bleeding and treatment over the pregnant uterus. Devices are regulated as medical devices and carry a laser class, and operators should be trained and work within local policy. Photobiomodulation itself is not prohibited in sport, since it is a physical therapy rather than a substance or a prohibited method, which makes it one of the more straightforward options in a competing athlete, although as always any accompanying injection or medication is a separate question.

• •Photobiomodulation (PBM), also called low-level laser therapy (LLLT), uses red or near-infrared light at intensities low enough to avoid heating tissue, and differs from surgical and high-intensity laser.
• •Cytochrome c oxidase in the mitochondrial respiratory chain is the leading proposed chromophore, with downstream effects on cellular energy, inflammatory mediators and nerve conduction.
• •Near-infrared light generally penetrates more deeply than visible red light, but exposure at the target also depends on power, beam characteristics, skin, tissue depth and technique.
• •Dose is defined by wavelength, power and time, with fluence in joules per square centimetre describing surface energy density rather than the dose reaching a deep target; the biphasic response is proposed rather than established.
• •An umbrella review found possible benefit for selected outcomes with mainly low or very low certainty; UK guidance advises against laser for osteoarthritis, and made no recommendation for chronic primary pain because evidence was too uncertain.
• •Eye protection must match the wavelength, device type and laser class, with a device-specific optical risk assessment for light-emitting diode systems; photobiomodulation is not prohibited in sport.