Contextual Effects on Inflammatory Biomarkers and Pain Relief After Spinal Joint Manipulation

The goal of this clinical trial is to learn whether contextual effects created by observational learning can change pain relief and inflammation-related biological responses after spinal joint manipulation in adults with chronic non-specific low back pain. The main questions it aims to answer are: Does positive, neutral, or negative observational learning change pain after spinal joint manipulation? Does it change disability, lumbar range of motion, stress, fear of movement, empathy, and treatment expectations? Does it change pressure pain threshold, lumbar tissue temperature, and blood markers related to inflammation, including interleukin-6 (IL-6), high-sensitivity C-reactive protein (hs-CRP), tumor necrosis factor alpha (TNF-α), and interleukin-10 (IL-10)? The researchers will compare 3 groups: a positive expectation group, a neutral group, and a negative expectation group. Before the treatment, each participant will have a short interaction with a trained simulated patient. The simulated patient will present a positive, neutral, or negative experience with spinal manipulation, depending on group assignment. After this, all the participants will receive the same spinal joint manipulation procedure. The participants will: * be randomly assigned to 1 of 3 study groups, * complete baseline questionnaires and clinical tests before treatment, * take part in a brief observational learning session before manipulation, * receive 1 spinal joint manipulation treatment, * complete outcome measurements before treatment, about 60 minutes after treatment, and 24 hours after treatment, * provide blood samples for analysis of inflammation-related biomarkers. This study will include adults aged 18 to 65 years with chronic non-specific low back pain. The main outcome is pain intensity. Secondary outcomes include disability, stress, empathy, fear of movement, lumbar range of motion, tissue temperature, pressure pain threshold, and treatment expectations. Exploratory outcomes i