Focal Extracorporeal Shock Wave Therapy With Two Different Dosing Regimens for Chronic Low Back Pain

Inclusion Criteria: * Individuals of both sexes. * Age between 18 and 65 years. * Clinical diagnosis of mechanical chronic low back pain (cLBP), defined as pain localized between the lower costal margin and the gluteal fold, with at least 12 weeks of evolution. * Lumbar pain intensity of at least 5/10 on the Numeric Pain Rating Scale (NPRS). * Predominantly mechanical pain, exacerbated by activities such as prolonged standing, trunk movements, extension, or lumbar rotation, and without clinical data of predominant radicular pain. * Plain radiograph of the lumbar spine available as part of the baseline evaluation. * Ability to attend all 4 treatment sessions and subsequent follow-up evaluations. * Signed informed consent form previously approved by the Institutional Review Board / Research Ethics Committee. Exclusion Criteria: * Low back pain of probable non-mechanical origin or secondary to a specific cause that substantially modifies clinical management. * Clinical data of predominant lumbar radiculopathy, including pain radiating below the knee with a dermatomal distribution, focal motor deficit, objective sensory alterations, or compatible reflex changes. * Diagnosis or suspicion of cauda equina syndrome. * History of previous lumbar spine surgery. * Current vertebral fracture or recent history of lumbar fracture. * Spondylolisthesis grade II or higher. * Significant structural scoliosis or severe lumbar deformity that prevents treatment standardization. * Suspicion or evidence of a tumor, infection, spondylodiscitis, or axial inflammatory disease. * Severe clinically documented osteoporosis or history of vertebral fragility fracture. * Pregnancy or lactation. * Coagulation disorder, use of anticoagulants at therapeutic doses, or a hemorrhagic condition that increases procedure risk. * Previous epidural infiltration, facet block, radiofrequency, or other lumbar interventional procedure within a recent period defined by the protocol. * Current treatment with another physical rehabilitation modality or instrumental therapy directed at low back pain, if it cannot be suspended during the intervention period. * Current use of nonsteroidal anti-inflammatory drugs (NSAIDs) that the patient cannot suspend according to the study indications. * Concomitant neurological, rheumatological, oncological, or musculoskeletal disease that significantly interferes with pain or disability evaluation. * Cognitive impairment, decompensated psychiatric disorder, or any condition that prevents understanding instructions, answering questionnaires, or completing follow-up.