The relationship between flexibility and EMG activity pattern of the erector spinae muscles during trunk flexion-extension

Background: Movements in the lumbar spine, including flexion and extension are governed by a complex neuromuscular system involving both active and passive units. Several biomechanical and clinical studies have shown the myoelectric activity reduction of the lumbar extensor muscles (flexion-relaxation phenomenon) during lumbar flexion from the upright standing posture. The relationship between flexibility and EMG activity pattern of the erector spinae during dynamic trunk flexion-extension task has not yet been completely discovered. Objective: The purpose of this study was to investigate the relationship between general and lumbar spine flexibility and EMG activity pattern of the erector spinae during the trunk flexion-extension task. Methods: Thirty healthy female college students were recruited in this study. General and lumbar spine flexibilities were measured by toe-touch and modified schober tests, respectively. During trunk flexion-extension, the surface electromyography (EMG) from the lumbar erector spinae muscles as well as flexion angles of the trunk, hip, lumbar spine and lumbar curvature were simultaneously recorded using a digital camera. The angle at which muscle activity diminished during flexion and initiated during extension was determined and subjected to linear regression analysis to detect the relationship between flexibility and EMG activity pattern of the erector spinae during trunk flexion-extension. Results: During flexion, the erector spinae muscles in individuals with higher toe-touch scores were relaxed in larger trunk and hip angles and reactivated earlier during extension according to these angles (P < 0.001) while in individuals with higher modified schober scores this muscle group was relaxed later and reactivated sooner in accordance with lumbar angle and curvature (P < 0.05). Toe-touch test were significantly correlated with trunk and hip angles while modified schober test showed a significant correlation with lumbar angle and curvature variables. Conclusion: The findings of this study indicate that flexibility plays an important role in trunk muscular recruitment pattern and the strategy of the CNS to provide stability. The results reinforce the possible role of flexibility alterations as a contributing factor to the motor control impairments. This study also shows that flexibility changes behavior is not unique among different regions of the body. (C) 2008 Elsevier Ltd. All rights reserved.