The purpose of this clinical trial is to evaluate and compare the efficacy of two different dosing regimens of focal extracorporeal shock wave therapy (F-ESWT) in patients diagnosed with chronic mechanical low back pain. Participants will be randomly assigned to one of two experimental groups to receive different parameters of shock wave intervention. The main objective is to determine which dosing scheme provides a more significant reduction in pain intensity and a better recovery of lumbar function.

Chronic mechanical low back pain is a common musculoskeletal condition that leads to functional disability and diminished quality of life. While focal extracorporeal shock wave therapy (F-ESWT) has emerged as a non-invasive treatment option to promote tissue regeneration and modulate inflammation, clinical protocols lack precise standardization regarding energy density and session distribution.

This randomized, double-blind clinical trial aims to analyze the clinical effects of two specific dosing regimens of F-ESWT. Eligible participants from the Physical Medicine and Rehabilitation Service will be randomly allocated to either Group A or Group B. Both groups will undergo targeted applications to the lumbar region using predefined therapeutic parameters detailed in the protocol.

Clinical evaluations will be performed at baseline and during post-treatment follow-up periods. Pain intensity, functional disability, and localized mobility will be measured using validated clinical tools to define which dosing scheme optimizes short-term and mid-term patient recovery.

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.

De-identified individual participant data underlying the results reported in future publications (including text, tables, and figures) will be made available to researchers for secondary academic and clinical analyses.

Data will become available beginning 6 months after main publication and will remain accessible for up to 3 years.

Data will be shared with qualified researchers who provide a methodologically sound proposal. Requests should be directed to the corresponding investigator.

A double-blind design will be implemented. Participants will not be informed of the specific dosing regimen parameters they are receiving during the applications. The outcomes assessor responsible for performing the baseline and post-treatment clinical evaluations will remain fully blinded to the group allocation of each participant throughout the study.