Table 1 Study eligibility and selection criteria

Inclusion criteria

Articles published (including those accepted for publication) in an indexed, peer reviewed journal, or a published^a thesis

Studies including patients with: disc herniation, facet arthrosis, and/or spinal canal stenosis identified via imaging; specific LBP with confirmed radicular leg pain or muscle weakness on clinical examination

Regional paraspinal muscle morphology assessed with imaging or biopsy for either the lumbar multifidus muscles (LMM), erector spinae muscles (ESM) (including subcomponents), psoas major muscles (PMM), or "paraspinal / paravertebral" muscles (PVM)

Observational human studies with a control or comparison analyses (controls included: "normal" or “non-diseased”; comparisons between different severities of conditions; participants serving as own control when there was a normal and an abnormal side to compare)

Clinical / surgical trials containing baseline data with relevant “pathology to muscle” or “clinical to muscle” comparisons

Exclusion criteria

History of previous lumbar spine surgery

Analysis was solely post-interventional (i.e., no pre-surgical, pre-treatment, or pre-activity/functional muscle measurement data analysed)

Case reports, editorials/letters, literature reviews, guidelines, and abstract-only publications

Patients with primary muscular disease (e.g., muscular dystrophy, parkinsonism)