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

Inclusion Criteria: * people with low back pain lasting longer than 3 months, aged 18 to 65 years, * highest reported pain intensity during the last 24 hours of at least 4 out of 10 on the 11-point Numeric Pain Rating Scale (NPRS-11), where 0 = no pain and 10 = worst imaginable pain, * clinical diagnosis of chronic non-specific low back pain (NSCLBP) based on symptoms located in the lumbar spine region and not on imaging findings, * no use of nonsteroidal anti-inflammatory drugs (NSAIDs) for at least 7 days before the study, * no use of pain medication for at least 24 hours before the study, * no use of corticosteroids, * no previous spinal manipulation therapy, * no alcohol, nicotine, or coffee consumption for at least 12 hours before the study, * written informed consent to participate in the study. Exclusion Criteria: * physiotherapy students, * presence of red flags, such as a history of cancer, constant or non-mechanical pain, progressive or radiating pain, sensory deficits in the trunk or - lower limbs, lower limb muscle weakness, or bladder/bowel dysfunction, * body mass index (BMI) greater than 30, * previous lumbar spine surgery, * lumbar spine injury within 6 months before the study, * diagnosed diabetes, * diagnosed rheumatic diseases, * affective disorders such as post-traumatic stress disorder (PTSD) or schizophrenia, * spondylolisthesis or spondylolysis confirmed by imaging, * diagnosed endometriosis, * use of hormonal medications, * sleep disorders, * shift work, * musculoskeletal injury within the last 14 days, * active infection, * pregnancy, * endocrine disorders such as hyperthyroidism or hypothyroidism, * use of opioid medications, including over-the-counter combination products such as codeine with paracetamol, * current or recent use of antidepressants affecting serotonin or dopamine (including SSRIs, SNRIs, tricyclic antidepressants, MAO inhibitors, or ketamine), * current diagnosis of major depressive disorder or bipolar disorder, as well as PTSD or schizophrenia, * ongoing psychotherapy during the study period, * cognitive impairment or significant hearing impairment that may interfere with understanding or processing the observational learning procedure.