Low back pain (LBP) is ranked as one of the most prevalent health conditions. It is likely that some inflammatory mediators could be associated with pain and disability in these patients. Photobiomodulation therapy (PBMT) is a non-pharmacological therapy often used in patients with LBP that decrease release of inflammatory mediators and accelerate muscle repair in different muscle skeletal conditions, as mechanisms of action. The present research project aims to evaluate the effects of PBMT on systemic levels of inflammatory markers and levels of pain intensity in patients with chronic non-specific low back pain.

This is a randomized, triple-blinded (therapist, assessor and patient), placebo-controlled trial, with voluntary patients with non-specific chronic low back pain.

Eighteen patients will be randomly allocated to two treatment groups: Placebo or PBMT and one single session of treatment will be provided.

The data will be collected by a blinded assessor and the outcomes of interest it will be levels of inflammatory markers and pain intensity and it will be collected at baseline and 15 minutes after the single session of treatment.

The statistical analysis will follow the intention-to-treat principles. The findings will be tested for their normality using the Shapiro-Wilk test. Parametric data will be expressed as mean and standard deviation and non-parametric data as median and respective upper and lower limits. Parametric data will be analyzed by two-way repeated measures analysis of variance (ANOVA; time versus experimental group) with post-hoc Bonferroni correction. Non-parametric data will be analyzed using the Friedman test and, secondarily, the Wilcoxon signed-rank test.

Inclusion Criteria:

• patients with chronic non-specific low back pain (defined as pain or discomfort between the costal margins and the inferior gluteal folds, with or without referred symptoms in the lower limbs, for at least 3 month);
• with a pain intensity of at least 3 points measured by a 0-10 points pain numerical rating scale;
• aged between 18 and 65 years;

Exclusion Criteria:

• evidence of nerve root compromise (i.e. one or more of motor, reflex or sensation deficit);
• serious spinal pathology (such as fracture, tumor, inflammatory and infectious diseases);
• serious cardiovascular and metabolic diseases;
• previous back surgery;
• pregnancy.
• severe skin diseases (eg. skin cancer, erysipelas, severe eczema, severe dermatitis, severe psoriasis and severe hives lupus);

The data will be available upon requested of principal investigator.

The mode of intervention (active or placebo PBMT) will be coded by an independent researcher. The randomization schedule will contain only codes (not the actual intervention). The output from the PBMT device is exactly the same from either the active or the placebo interventions. These features will guarantee that participants, therapists and outcomes assessor will be blinded to the treatment arms.