Investigation of Flexion-Relaxation Ratio Symmetry in Subjects with and without Non-Specific Chronic Neck Pain

Introduction: Neuromuscular imbalance between right and left sides of Cervical Erector Spinae (CES) muscles can induce pain by applying the asymmetric loads on the spine incorrectly. This study evaluated the symmetry of the right and left cervical flexion-relaxation ratio (FRR) in patients with Non-Specific Chronic Neck Pain (NSCNP) and healthy subjects.We aimed to investigate the symmetry of FRR on the right and left sides of the CES muscles in individuals with and without NSCNP. Materials and Methods: A total of 25 patients with NSCNP and 25 healthy subjects participated in this study. The surface electromyography activity of CES muscles during four phases of flexion and extension tasks were measured and recorded. Unilateral FRR in the right and left sides of CES muscles was calculated and compared in each group. Results: Only in NSCNP patients, FRR in the right CES muscle was significantly higher than that in the left one (P 0.05). Also, FRR for bilateral CES muscles was significantly higher in healthy subjects than in NSCNP patients (P 0.001). Conclusion: The study results indicated a greater FRR asymmetry in CES muscles in NSCNP patients than in healthy subjects. This asymmetry is probably due to the dominance of the limb. Moreover, asymmetric FRR as a kind of neuromuscular imbalance may cause pain due to imposing asymmetric loads on spine structures.