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Laser photobiomodulation (PBM) or low-level laser therapy (LLLT) is a form of phototherapy recognized worldwide for its expansive use in medicine. PBM/LLLT has the ability to enhance enzymatic activity and mitochondrial transmembrane potential that increase the availability of energy and the signal transduction, which promotes cell proliferation. This study primarily investigates the appropriateness of a range of treatment parameters, including light wavelength, irradiance (doses) and exposure time of PBM/LLLT in proliferation of cultured human monocytic leukaemia cell line THP-1(Tamm-Horsfall Protein 1), as well as DNA under in vitro conditions. A secondary objective was to exploit the beneficial effect of PBM/LLLT to reduce the harmful impacts caused by exposure to ultraviolet (UV) radiation. Cells were irradiated with near infrared (NIR) diode laser at 850 nm with doses ranging from 0 – 26.8 J/cm2. After irradiation, cells were incubated for 12 hr and 24 hr to allow time for proliferation. Comet assay was conducted to evaluate genotoxicity of the irradiated cells. Trypan blue exclusion test and MTT assay (3-4-5-dimethy-2.5 thiazol-2.5 diphenyl tetrazolium bromide) were used to estimate cytotoxicity, Exposure to NIR diode laser revealed the beneficial effect of PBM/LLLT at low doses (< 5 J/cm2), which increased the viability and proliferation of THP-1 cells, which conformed by increasing ATP synthesis and the activity of mitochondria. Comet assay showed no significant difference between irradiated and non-irradiated cells at low doses and showed no DNA damage. The photobiomodulation effect of low doses, in particular 0.6 J/cm2 and 1.2 J/cm2, managed to reduce the damage to THP-1 cells after exposure to UV radiation by decreasing cell apoptosis, accelerate DNA damage repair and increase cell survival. While, the exposure for high doses (> 5 J/cm2), showed different results involved decrease in the number of THP-1 cells and viability, in addition to a considerable increase in DNA damage, which emphasised by decrease in the level of ATP synthesis and reducing the mitochondrial activity. These findings demonstrated the photobiomodulation effect of NIR diode laser through modulating various pathways such as ATP synthesis and mitochondrial activity in monocyte cells and DNA.

Most current interventions for improving cognition in older adults have proven unsuccessful in producing enduring effects, though non-invasive brain stimulation techniques including low-level laser therapy (LLLT) show promise in this regard. The aim of the present study was to determine whether or not physiological changes involving the right superior frontal gyrus, following its stimulation via LLLT, could induce changes in working memory, as measured by a multilevel in-scanner N-back task. Ninety-eight adults (ages 45 and over) with (n = 36) and without (n = 62) mild cognitive impairment were included in this study. It was hypothesized that, relative to adults receiving placebo, individuals treated with LLLT would exhibit strengthened load-dependent functional coupling between this region and other brain regions involved in WM leading to better performance accuracy and faster reaction times on the N-back task. Results showed no differences in performance accuracy (t = 1.02, p = 0.312) or reaction times (t = -0.82, p = 0.413) between treatment groups. Functional connectivity between the right SFG and bilateral occipital gyri and bilateral precuneus regions was strengthened in those who received LLLT but reduced in the placebo group. The LLLT group exhibited reduced functional coupling between the right SFG and paracentral lobule, cingulate cortex, precentral gyrus, middle frontal gyrus, and insula, whereas these connections were strengthened in the placebo group. The absence of change on behavioral outcome measures makes it difficult to contextualize these physiological changes, but the findings seem to suggest excessive engagement in the task following treatment, as well as insufficient deactivation of the default mode network. Follow-up studies are necessary to determine the capacity of LLLT to improve cognition in other domains not investigated by the present study. As well, further insight into the potential of LLLT could be gained through investigations of LLLT in conjunction with cognitive training interventions, as is often the case with alternative neurostimulation therapies.

Optimal performance in sport requires a balance between training stress and recovery. Therapeutic modalities that allow athletes to maintain this balance while training hard are in high demand, but many lack research. Photobiomodulation is a red and near-infrared light therapy that is proposed to enhance exercise performance and hasten recovery. The purpose of this study was to examine the effects of acute whole body photobiomodulation, applied pre-exercise, on anaerobic exercise performance. Forty-eight healthy, active subjects participated in this single-blind, crossover study. Subjects visited the lab three times to complete a repeat Wingate test, with one week between each visit. All subjects completed baseline testing during their first visit and randomly received either the photobiomodulation or placebo condition before testing on the second visit, followed by the opposite condition on the third visit. There was a significantly higher peak power on the first Wingate test following photobiomodulation (p=0.046) but no differences in peak power on the second, third, and fourth Wingate tests. There was also a significantly higher power drop on the first Wingate test (p=0.045) but no differences on the second, third, and fourth Wingate tests. There were no differences in average power on any of the Wingate tests. Blood lactate was significantly lower following photobiomodulation, before exercise (p=0.0001), trending higher after the first Wingate test (p=0.077), and significantly higher after the second Wingate test (p=0.048). Peak heart rate was significantly higher following photobiomodulation on the first (p=0.009), second (p=0.022), and fourth (p=0.015) Wingate tests. On the day following photobiomodulation, heart rate variability was higher (p=0.0043) but there were no differences in subjective recovery and stress scores. Based on these findings, we concluded that acute photobiomodulation may enhance maximal anaerobic performance but does not attenuate fatigue. We also concluded that acute photobiomodulation may enhance recovery from maximal, anaerobic exercise.

Delayed onset muscle soreness (DOMS) is a set of symptoms including muscle soreness and a decrease in muscle function and strength that present 24-48 hours post eccentric or unaccustomed-to exercise. Low-level laser therapy (LLLT) has been shown to be effective in attenuating DOMS symptoms. The purpose of this study was to determine the effectiveness of LLLT in the management of DOMS when delivered pre- and post- exercise protocol. Twenty-seven male volunteers were recruited and randomly assigned into one of three groups (LLLT, sham, control). All subjects underwent an eccentric exercise protocol of their elbow flexors. Pain, muscle function, and muscle strength were assessed prior to, 24, and 48 hours after the exercise protocol. Subjects received their treatment intervention before, immediately after the exercise protocol, and 24-hours after the exercise protocol. Subjects in the sham group had identical set-up as those in the LLLT group; however they did not receive an active LLLT treatment. The control group sat quietly and did not receive treatment. There was no significant group by time interactions for pain, function, or strength. There was also no significant time main effect for function. There was a significant time main effect for pain and strength. To our knowledge, this study was the first to explore the effects of LLLT and DOMS when delivered both pre- and post- eccentric exercise. Although LLLT was found ineffective for treating those symptoms of DOMS at our chosen parameters, previous literature has shown that LLLT has promising effects on attenuating symptoms of DOMS.

For understanding the mechanisms of low level laser/light therapy (LLLT), accurate knowledge of light interaction with tissue is necessary. In order to have a successful therapy, laser energy needs to be delivered effectively to the target location which depending on the application can be within various layers of skin or deeper. The energy deposition is controlled by input parameters such as wavelength, beam profile and laser power, which should be selected appropriately. This thesis reports a numerical study that investigates the laser penetration through the human skin and also provides a scale for selection of wavelength, beam profile and laser power for therapeutic applications. First, human skin is modeled as a three-layer participating medium, namely epidermis, dermis, and subcutaneous, where its geometrical and optical properties were obtained from the literature. Both refraction and reflection are taken into account at the boundaries according to Snell’s law and Fresnel relations. Then, a three dimensional multi-layer reduced-variance Monte Carlo tool was implemented to simulate the laser penetration and absorption through the skin. Local profiles of light penetration and volumetric absorption densities were simulated for uniform as well as Gaussian profile beams with different spreads at 155 mW average power over the spectral range from 1000 nm to 1900 nm. The results showed that lasers within this wavelength range could be used to effectively and safely deliver energy to specific skin layers as well as to achieve large penetration depths for treating deep tissues, without causing any skin damage. In addition, by changing the beam profile from uniform to Gaussian, the local volumetric dosage could be increased as much as three times for otherwise similar lasers. In the second part of this thesis, a three-dimensional single-layer reduced-variance inverse Monte Carlo method was developed to find the optical properties of the skin using the experimental values of transmittance and reflectance. The results showed that both transmittance and reflectance scale well with transport optical thickness. Moreover, it was also shown that penetration depth is highly sensitive to the laser wavelength and varied within the range from 1.7 mm to 4.5 mm.