Flexion-Relaxation Ratio Asymmetry and Its Relation With Trunk Lateral ROM in Individuals With and Without Chronic Nonspecific Low Back Pain

Abstract

A cross-sectional comparative study. The present study aimed to investigate the relationship between the FR phenomenon asymmetry of lumbar muscles and trunk lateral range of motion (ROM) asymmetry in nonspecific chronic low back pain (NSCLBP) patients. Imbalance in trunk muscle activation between right and left sides can induce pain by loading the spine incorrectly, especially in patients with NSCLBP. A previous study reported a greater asymmetry in the FR phenomenon of the erector spinae in NSCLBP patients than in asymptomatic participants (APs). Imbalance of muscle properties, such as trunk ROM, has been suggested as a possible cause of this observed asymmetry. Twenty-eight NSCLBP patients and 22 AP performed 3 standing maximal trunk flexions. Surface electromyography was recorded bilaterally for erector spinae longissimus and lumbar multifidus. A FR ratio was calculated for each muscle. The fingertip-to-thigh test was performed to assess trunk lateral ROM. Each parameter's asymmetry was calculated as the absolute difference between right and left sides. NSCLBP patients present a significantly lower trunk lateral ROM than AP. FR ratio asymmetry of the erector spinae was significantly greater in NSCLBP patients than in AP (P < 0.05). FR ratio asymmetry of the multifidus and trunk lateral ROM asymmetry were not significantly different between groups. Significant correlation (r = 0.49) between FR ratio asymmetry of erector spinae and trunk lateral ROM asymmetry was observed only for patients with NSCLBP. The present findings showed that FR ratio asymmetry of erector spinae longissimus is moderately correlated with trunk lateral ROM asymmetry. In addition, the results confirmed that patients with NSCLBP present a reduced trunk lateral ROM, a FR ratio asymmetry of the erector spinae which is correlated with trunk rotation. These findings suggested an imbalance spine loading which can contribute to the persistence of pain. 3.