According to the American College of Rheumatology (ACR), fibromyalgia is a chronic musculoskeletal condition characterized by generalized pain for at least three months in combination with sensitivity in 11 or more of the 18 points sensitive to palpation in different parts of the body, known as tender points [1, 2]. Fibromyalgia was not a clinically well-defined condition before the 1970s, and unlike what was thought in the past, this is not an inflammatory condition and does not lead to joint impairment or deformities. However, the chronic nature of this condition has a negative impact on quality of life .
The most widely accepted theory is that fibromyalgia is caused by an abnormality in pain modulation mechanisms - a central nervous system disorder in regulating sensitivity to pain. Thus, an individual may exhibit a reduction in serotonin (neurotransmitter of the inhibitory descending system) and in increase substance P (neuroexcitatory substance involved in the conduction of pain) in the central nervous system .
Fibromyalgia is often associated with other syndromes, such as fatigue, sleep disorders, morning stiffness and psychological disorders, such as anxiety and depression. Sleep disorders are closely linked to somatic symptoms in patients with fibromyalgia and not to their personality. The most common complaints are difficulty falling asleep, frequent awakening during the night, difficulty getting back to sleep, restless superficial sleep and early rising, the consequences of which are nonrestorative sleep and a sensation of weariness, which contribute toward a poor quality of life. Thus, non-restorative sleep is an important aspect among the manifestations of fibromyalgia, which makes the investigation into primary sleep disorders essential to the assessment of affected individuals [5, 6]. The complexity of the factors involved regarding both diagnosis and adequate treatment underscores the need for further studies aimed at broadening knowledge on the effects of this condition on patients.
There are several treatment options for fibromyalgia, such as drugs [7, 8], psychotherapy , hydrotherapy , electrotherapy , exercise  and laser therapy [13, 14]. However, there is no consensus or defined protocol regarding the use of these treatment options. Low-level laser therapy (LLLT) is one of the more recent pain treatment modalities in the field of physical therapy. According to Laakso et al. , the analgesic effect of phototherapy may be mediated by hormonal/opioid mechanisms, the responses of which depend directly on the dose and wavelength used to irradiate the tissue. Thus, the parameters directly affect the results. LLLT is also reported to act on peripheral neural stimulation and the regulation of microcirculation, interrupting pain mechanisms and promoting analgesia . The normalization of microcirculation and the capacity of neural transmission obtained through laser therapy have been described as responsible for the interruption of the vicious circle that gives rises to and perpetuates pain .
In last ten years, important advances have occurred in the therapeutic use of photobiostimulation with low-level lasers. Such advances have occurred due to a greater understanding of the mechanisms of action involved as well as technological developments and the publication of relevant studies and research related to the advantages obtained with the use photobiostimulation in clinical practice. However, the lack of consensus regarding therapeutic protocols hinders multicenter comparisons of the many clinical trials published. Thus, a number of scientific papers have been drafted to establish a therapeutic protocol for the use of photobiostimulation with regard to exposure time, intensity, energy density, application mode and application site.
A considerable number of studies have demonstrated the remission of pain in patients with fibromyalgia through the use of LLLT. However, this is not yet a well-established therapy and comparisons of controlled clinical trials are rare. Moreover, there are problems regarding the standardization of treatment [13, 14, 17, 18]. In the investigation of complex phenomena such as fibromyalgia, the application of multiple methodological techniques enables a better assessment and understanding of such phenomena .
The aim of the proposed study is to assess the analgesic effect of LLLT on tender points in patients with fibromyalgia and establish correlations with quality of life and sleep.