The METRIC Study Protocol

Inclusion Criteria: * Duration of current low back pain (LBP) episode ≥ 6 months; * Average LBP intensity during the last 7 days ≥ 3/10; * (For healthy volunteers only) To be of the same sex and age (± 1 year) as a participant with low back pain. Exclusion Criteria: * Diagnosis of back conditions other than chronic primary LBP e.g., failed back surgery syndrome, spondylosis, spondylolisthesis, spinal stenosis, herniated disc, infection, etc.; * Presence of pain in another body location that is more severe than the pain in the lower back; * Presence of a neurological deficit i.e., sensation loss, muscle weakness, decreased deep tendon reflexes; * Presence of contraindications to spinal manipulative therapy e.g., recent fracture, history of spinal surgery, cauda equina syndrome, inflammatory arthritis, taking anticoagulant medication, active cancer, moderate to severe osteoporosis, abdominal aortic aneurysm; * Underwent surgery in the last 3 months; * Pregnancy, ≤ 3 months post-partum or planning to get pregnant in the next 12 months; * History of spinal manipulative therapy in the past 12 months; * Scoliosis ≥ 20°; * BMI ≥ 40; * Insufficient language skills in French to complete the questionnaires; * Open or pending litigation for LBP or seeking/receiving disability compensation; * Diagnosis of an illness affecting the sensorimotor functions e.g., diabetes, multiple sclerosis, amyotrophic lateral sclerosis; * Diagnosis of mental health disorders (with the exception of anxiety and depression); * Current drug or alcohol dependence; * Skin of type I on the Fitzpatrick scale; * (For healthy volunteers only) Regular use of pain medication or usage in the 48 h prior to data collection; * (For healthy volunteers only) History of chronic pain; * (For healthy volunteers only) Acute pain on the days of data collection.