Participants allocated to this group will receive Cognitive Functional Therapy (CFT), a physiotherapy-led intervention targeting pain-related behaviors, beliefs, and functional limitations. The program includes individualized sessions focusing on making sense of pain, exposure with control, and lifestyle changes. Sessions will be delivered weekly over a period of up to 12 weeks. The physiotherapist--researcher has completed more than 80 hours of training, including in--person and online courses, supervisions and interactive case discussions with feedback by physical therapists with more than 10 years of clinical experience using CFT in Brazil.

Participants allocated to this group will receive sham photobiomodulation combined with neutral talking. The intervention is designed to control for non-specific effects such as therapist attention and interaction, without delivering an active intervention. Sessions will be conducted weekly over the study period.

Participants will receive up to eight sessions of Cognitive Functional Therapy (CFT), each lasting 50 minutes, delivered once per week over a maximum of 12 weeks; the first session will last 60 minutes. Weekly reminders will be provided to enhance adherence.

All participants will receive an educational booklet addressing chronic pain, maladaptive beliefs, and unhelpful pain-related behaviors. The intervention includes individualized strategies aimed at improving pain understanding, reducing protective behaviors, promoting functional movement, and supporting lifestyle changes. The program also incorporates strategies for autonomous management of symptom exacerbations.

The fidelity of the CFT intervention will be monitored through recorded sessions throughout the clinical trial. Recordings will be made for every seven participants allocated to the CFT group. Three researchers with expertise in the CFT will watch the recorded videos and provide feedback to the treating physiotherapist.

Disability due to low back pain (LBP), assessed using the Oswestry Disability Index (ODI; 0-100) at post-treatment (12 weeks), will be the primary outcome measure.

The ODI was originally developed by Fairbank et al. (1980) and consists of 10 items, each with six response options. The version adapted and validated for Brazilian Portuguese was proposed by Vigatto et al. (2007). The total score will be calculated by summing the items, with a maximum score of 50 points, which is subsequently converted into a percentage (0 to 100), with higher scores indicating greater functional disability.

The Numeric Pain Rating Scale (NPRS), which will be administered verbally in this study in the form of an interview at the time of assessment, is a unidimensional measure that is easy to apply across different cultures and languages, and has been validated for assessing pain intensity in adults. It consists of 11 integer points ranging from 0 to 10, where 0 represents "no pain" and 10 represents "the worst imaginable pain" (Childs, Piva, & Fritz, 2005).

Lower NPRS scores indicate lower pain intensity, which can be qualitatively classified as mild (1-3 points), moderate (4-6 points), and severe (7-10 points).