Objectives: The aim of this study was to review the biomedical literature to ascertain the biomechanical and clinical significance of the lumbar erector spinae flexion-relaxation phenomenon (FRP).
Data sources: Index Medicus via PubMed, the Noble Science Library's e-journal archives, and the Manual Alternative and Natural Therapy Index System databases were searched using the same search terms.
Discussion: The presence of the FRP during trunk flexion represents myoelectric silence consistent with increased load sharing of the posterior discoligamentous passive structures. Passive contributions from erector spinae stretching during the flexion posture and active contributions from other muscles (quadratus lumborum and deep erector spinae among others) further assist in load sharing in the trunk flexion posture. A number of studies have shown differences in the FRP between patients with chronic low back pain and healthy individuals, and the reliability of the assessment. Persistent activation of the lumbar erector spinae musculature among patients with back pain may represent the body's attempt to stabilize injured or diseased spinal structures via reflexogenic ligamentomuscular activation thereby protecting them from further injury and avoiding pain.
Conclusions: The myoelectric silencing of the erector spinae muscles in the trunk flexion posture is indicative of increased load sharing on passive structures, which tissues have been found to fail under excessive loading conditions and shown to be a source of low back pain. The studies that show differences in the presence of the FRP among patients and control subjects are encouraging for this type of clinical assessment and suggest that assessment of the FRP is a valuable objective clinical tool to aid in the diagnosis and treatment of patients with low back pain.