Myofascial pain syndrome is characterized by trigger points (TPs), which cause pain in muscles and fasciae. Low-Level Laser Therapy (LLLT) has shown potential in treating TPs, contributing to pain reduction and the inflammatory process. However, inhibitory doses remain underexplored for this condition. TP formation is associated with a knot in the muscle fiber, leading to local vasoconstriction, but it may also contain inflammatory mediators. This creates a challenge in thermographic characterization, as a TP may present as either a colder region, due to vasoconstriction, or a warmer one, due to inflammation.

To assess whether a dosage of 16J of 808nm LLLT induces changes in pain and skin temperature in individuals with TPs in the trapezius.

This is a double-blind, sham-controlled, randomized clinical trial with 52 volunteers of both sexes (= 18 years old) experiencing spontaneous trapezius pain for over three months and diagnosed with TPs. Sixty participants will be randomly assigned to two equal groups: LLLT group (LLLTG), treated with an 808nm laser (16J) applied to TPs in the upper trapezius; and Sham group (SHAMG), which will receive the same protocol with a placebo LLLT. The treatment will consist of eight sessions, twice a week, over four weeks, with participants lying in a supine position, with their cervical spine in a neutral position. Pain perception (Numeric Pain Rating Scale), skin temperature (Tsk) (E54 thermographic camera, FLIR, USA), presence of TPs (palpation), and cervical disability index (Neck Disability Index) will be assessed at three time points: before, immediately after, and 48 hours post-protocol. The global perceived effect (GPE) will be evaluated after the final session and 48 hours later. The primary outcomes will be pain and Tsk. Statistical analysis will use linear mixed models in SPSS, and a Q-Q plot will be generated to check for normal distribution of the data.

It is expected that the LLLT treatment protocol with an inhibitory dose of 16J on the trapezius will significantly reduce pain compared to the Sham group. Regarding skin temperature, it may increase if vasodilation is the predominant response to LLLT or decrease if there is a reduction in metabolic activity and inflammatory mediators. Improvements in the Neck Disability Index and global perception of improvement are also expected.

The findings of this study may provide evidence on the effects of the inhibitory dose of LLLT on pain and skin temperature in individuals with TPs. If the therapy proves effective, these results could contribute to the refinement of clinical follow-up and rehabilitation protocols.

The results may directly impact clinical practice by supporting a more effective treatment for TPs. If LLLT with an inhibitory dose demonstrates positive effects in reducing pain and modulating temperature, its application could serve as an alternative for the management of trigger points, expanding therapeutic options for physical therapists and other healthcare professionals. Meanwhile, thermography may serve as a useful tool for monitoring treatment responses.