Nov 15, 2016
Seeing the Light
Dr. Timothy Demchak

Photobiomodulation therapy (PBM) — sometimes called low-level laser therapy, cold laser, light therapy, and phototherapy — has numerous potential therapeutic outcomes. Defined as a light therapy that utilizes non-ionizing light to elicit photophysical and photochemical events at various biological scales through non-thermal processes, PBM may decrease pain and inflammation, facilitate immunomodulation, and promote tissue healing.

Light from a laser is monochromatic (single wavelength), coherent, and collimated, which means it stays together in a beam. This is why a laser pointer works from across the room.

Light interacts with tissue primarily in four ways: transmission through the skin, absorption by other chromophores, scattering, and reflection. The amount of light that reaches a targeted area in, such as injured tissue or bone, depends on the wavelength, dose, and the presence other chromophores in the skin (such as melanin, blood, tattoos). Lasers for photobiomodulation therapy should be in the 600 nm to 1070 nm range to effectively penetrate the skin. Specifically, wavelengths in the 600-700 nm range are used to treat superficial tissue and longer wavelengths (780-1070 nm) are better for reaching deeper tissue.

Next, the clinician should figure out the optimal dosage of light. Dose is either listed as energy measured in joules (J) (watt x time) or energy density (J/cm2). The actual amount of energy that reaches the target tissue is the dose minus the amount of energy absorbed (which will depend on wavelength, skin color, blood, tattoos, etc.) and energy reflected from the skin (which will depend on application technique, such as contact vs off contact).

The light that is transmitted through the skin has to be absorbed by a receptor or chromophore in order to have an effect. The main chromophore that absorbs light is cytochrome c oxidase (CCO), located in the mitochondria.

Once absorbed, light can trigger a wide range of physiological mechanisms on the molecular, cellular, and tissue levels. PBM has a bi-phasic dose response, meaning the treatment either stimulates or inhibits physiological processes. Low doses of light have a stimulatory effect, which accelerates the production of adenosine triphosphate (ATP), increasing the amount of energy available to promote tissue healing. Reactive oxygen species are also released. These activate transcription factors that cause an upregulation of various stimulatory and protective genes linked to cell proliferation, migration, and the production of growth factors — all of which speed up healing. Additionally, nitric oxide dissociation from CCO will increase ATP production and cause vasodilation. This increases the blood flow to a specific area, boosting its concentration of oxygen and immune cells and accelerating healing.

On the other side of the spectrum, there is strong evidence that a high dose of light inhibits acute, chronic, and neurological pain by reducing the formation of prostaglandin, cyclooxygenase 2 (COX-2), and tumor necrosis factor alpha (TNF-α). Prostaglandin sensitizes nociceptors, which makes them hypersensitive. COX-2 is specific to inflammatory processes related to injury, and TNF-α plays a role in chronic inflammation and pain.

Beyond its application with healing and pain reduction, a meta-analysis recently showed strong evidence that PBM can improve muscular performance and accelerate recovery, as well. In a 12-week randomized control training study, PBM treatment applied to the quadriceps prior to exercise resulted in increased muscular strength three times faster than the placebo. The increase was in maximum voluntary contraction and both leg press and leg extension one-repetition maximums.

From boosted healing to inhibited pain to increased muscular performance, PBM has a variety of applications for therapy. With some background knowledge and a familiarity with proper dosing procedure, it can be a welcome addition to any athletic training room.

The light that is transmitted through the skin has to be absorbed by a receptor or chromophore in order to have an effect. The main chromophore that absorbs light is cytochrome c oxidase (CCO), located in the mitochondria.

Once absorbed, light can trigger a wide range of physiological mechanisms on the molecular, cellular, and tissue levels. PBM has a bi-phasic dose response, meaning the treatment either stimulates or inhibits physiological processes. Low doses of light have a stimulatory effect, which accelerates the production of adenosine triphosphate (ATP), increasing the amount of energy available to promote tissue healing. Reactive oxygen species are also released. These activate transcription factors that cause an upregulation of various stimulatory and protective genes linked to cell proliferation, migration, and the production of growth factors — all of which speed up healing. Additionally, nitric oxide dissociation from CCO will increase ATP production and cause vasodilation. This increases the blood flow to a specific area, boosting its concentration of oxygen and immune cells and accelerating healing.

On the other side of the spectrum, there is strong evidence that a high dose of light inhibits acute, chronic, and neurological pain by reducing the formation of prostaglandin, cyclooxygenase 2 (COX-2), and tumor necrosis factor alpha (TNF-α). Prostaglandin sensitizes nociceptors, which makes them hypersensitive. COX-2 is specific to inflammatory processes related to injury, and TNF-α plays a role in chronic inflammation and pain.

Beyond its application with healing and pain reduction, a meta-analysis recently showed strong evidence that PBM can improve muscular performance and accelerate recovery, as well. In a 12-week randomized control training study, PBM treatment applied to the quadriceps prior to exercise resulted in increased muscular strength three times faster than the placebo. The increase was in maximum voluntary contraction and both leg press and leg extension one-repetition maximums.

From boosted healing to inhibited pain to increased muscular performance, PBM has a variety of applications for therapy. With some background knowledge and a familiarity with proper dosing procedure, it can be a welcome addition to any athletic training room.

References

Allemann I, Kaufman J, “Laser Principles,” Curr Probl Dermatol, vol. 42, no. pp. 7-23, 2011.

Chung H, Dai T, Sharma SK, Huang YY, Carroll JD, Hamblin MR, “The nuts and bolts of low-level laser (light) therapy,” Ann Biomed Eng, vol. 40, no. 2, pp. 516-533, 2012.

Bjordal JM, Johnson MI, Iversen V, Aimbire F, Lopes-Martins RA, “Low-level laser therapy in acute pain: a systematic review of possible mechanisms of action and clinical effects in randomized placebo-controlled trials,” Photomed Laser Surg, vol. 24, no. 2, pp. 158-168, 2006.

Leal-Junior EC, Vanin AA, Miranda EF, de Carvalho Pde T, Dal Corso S, Bjordal JM, “Effect of phototherapy (low-level laser therapy and light-emitting diode therapy) on exercise performance and markers of exercise recovery: a systematic review with meta-analysis,” Lasers Med Sci, vol. 30, no. 2, pp. 925-939, 2015.

Vanin AA, Miranda EF, Machado CS, et al., “What is the best moment to apply phototherapy when associated to a strength training program? A randomized, double-blinded, placebo-controlled trial : Phototherapy in association to strength training,” Lasers Med Sci, vol. no. pp. 2016.


Timothy Demchak, PhD, ATC, is a Professor in the Department of Applied Medicine and Rehabilitation at Indiana State University. He's conducted dozens of studies on therapeutic modalities, including the effects of laser and light therapy. Dr. Demchak can be reached at: [email protected]


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