Now for the additional science bit for the nerds out there (Like me)!

For low-power visible or near-infrared light to have an effect on a biological system, the photon must be absorbed by electronic absorption bands belonging to a photon acceptor or chromophore (a chromophore is a molecule, or portion of a molecule, which imparts a colour to a compound). Mitochondria, (everyone remembers from biology lessons), are known as the ‘powerhouse of the cell’. Mitochondria convert food molecules and oxygen into energy (ATP) by oxidative phosphorylation. It has been proposed that cytochrome c oxidase (Complex IV) is the primary photo-acceptor for the red-NIR wavelength range in mammalian cells. Nitric oxide (NO) produced in mitochondria can inhibit respiration by binding to Complex IV and displace oxygen especially in injured or hypoxic cells, reducing their capacity. It is proposed that Laser therapy can photo-dissociate NO from Complex IV and reverse the mitochondrial inhibition of respiration due to excessive NO binding. This results in activation of the cell-signaling mechanisms that promote proliferation and differentiation to provide an anti-inflammatory environment tightly regulated by the manipulation of oxidative and nitrative stress.

Basically, it is suggested that laser therapy, if absorbed by the cell in the correct area, promotes the efficacy of mitochondria at their role in cellular respiration. Therefore are more effective at providing cells with energy. In theory making them more likely to work more effectively, heal or regenerate faster. For Laser to be effective, the irradiation parameters (wavelength, power, power density, pulse parameters, energy density, total energy and time) need to be within certain ranges. The “optical window” in a tissue describes a range of wavelengths where the penetration of light into tissue is maximised by employing red and near-infrared wavelengths.

What is the evidence?

It is extremely challenging to compare Laser therapy to other treatments, as studies using Laser therapy are complicated by different lengths of treatment, different machines, and without standardisation of wavelengths and dosages.  

Pain

The peripheral nerve endings of nociceptors, consisting of the thinly myelinated and unmyelinated, slow-conducting C fibres, lie within the epidermis (the skin). In the pain pathway, this network of nerve fibres is used to transduce noxious (painful) stimuli into action potentials – to protect you from harm. These nerve endings are very superficial in nature and thus are within the penetration depths of the wavelengths used in Laser therapy. It is this theory that means there are several painful conditions that are suspected to be benefited by using laser therapy.

In one study, repeated treatment with a low-power laser produced relief in subjects with chronic pain. Analgesia was observed after exposure of the skin overlying the radial, medial and saphenous nerves; and in some cases, irradiation of the appropriate painful nerve. What this suggests is that when attempting to treat animals for chronic pain, we shouldn’t necessarily just be focusing on the painful area (e.g. it has hip pain so let’s use the laser on the hip). But more specifically, and indeed with great knowledge of anatomy, be focusing on the specific peripheral nerves associated with the pain.

Wound/Muscle/Tendon and Ligament Healing

Laser therapy at low doses has been shown to enhance cell proliferation (multiplication) of: Fibroblasts – cells that synthesise the extracellular matrix and collagen, produce the structural framework (stroma) for animal tissues, and play a critical role in wound healing

Keratinocytes – the primary type of cell found in the epidermis, the outermost layer of the skin)

Endothelial cells lining blood vessels

Lymphocytes – immune cells that are made in the bone marrow and are found in the blood and in lymph tissue). 

All fairly useful cells when it comes to healing! The mechanism of proliferation is thought to result from photo-stimulation of the mitochondria. This leads to activation of signalling pathways and up regulation of transcription factors. Eventually, this gives rise to increasing levels of growth factors, triggering increased cell multiplication. Laser therapy can also enhance neovascularisation (the formation of new blood vessels); promote angiogenesis (the development of blood vessels); and increase collagen synthesis to aid in the healing of acute and chronic wounds.