YOga for Patients With Chronic BACK Pain and Poor PROgnosis

Inclusion Criteria: * report chronic nonspecific LBP, defined as pain and discomfort localized below the costal margin and above the inferior gluteal folds, with or without leg pain and of at least 3 months' duration. * score ≥ 50 points (out of 100) in the Orebro Musculoskeletal Pain Questionnaire. * have an average back pain intensity of 3 points or more on a 0-10 numerical pain rating scale. Exclusion Criteria: * serious spine pathology (e.g. tumors, fractures, and inflammatory diseases). * nerve root compromise (i.e. at least 2 of the following signs: weakness, reflex change, or sensation loss associated with the same spinal nerve). * previos spinal surgery. * pregnancy or having given birth within the previous 3 months. * any medical condition that prevented being physically active (e.g., serious cardiovascular, kidney or neurological diseases). * any other musculoskeletal condition that may affect activity and movement participation in a Yoga program during the last year. * not currently receiving other physical activity-based intervention (e.g., Pilates, physical therapy, aquatic exercise). * inadequate Portuguese literacy for the study's questionnaires and instructions.