EMG Analysis of Latissimus Dorsi, Middle Trapezius, and Erector Spinae Muscle Activity during Return to Neutral Phase of Spinal Rotation

Purpose/Hypothesis: Rotation of the spine is a common movement used to perform activities of daily living and sports performance, and contributes to a large percentage of low back injuries. Performance of spinal rotation for the rehabilitation and prevention of future back injuries should be considered, as low back pain is the second most common reason for a physician visit. Muscles that are involved in rotation of the spine have been studied, but the Latissimus Dorsi (LD) has limited research on the influence of spinal rotation. The LD muscle is one of the largest back muscles and influences many movements of the trunk and limbs, and many attachment sites including the humerus, pelvis, ribs, spine, and scapula. The purpose of this study is to understand the muscle activity of the LD, middle trapezius (MT), and erector spinae (ES) during the movement from full hip rotation to neutral in a standing (non-fixed) and quadruped (fixed) position. Materials/Methods: Twenty-six healthy subjects (17 female) between 20-40 years of age volunteered to be a part of this study. All muscle activity being tested in this study was recorded using surface EMG electrodes while the subject performed left and right spinal rotation in standing and quadruped positions. Four spinal rotation test positions (standing rotation right/left, quadruped rotation right/left) were initiated by movement at the pelvis. A Maximal Voluntary Contraction (MVC) recorded in the prone position was used to normalize the muscle activity of the muscles being tested, and findings were analyzed for significance at ⍺=0.05. EMG data was collected and analyzed using Noraxon MyoResearchXP software. Results: Statistically significant differences were present in the ipsilateral and contralateral LD with upper extremities in a fixed position compared to non-fixed during the movement from full hip rotation to neutral. The mean EMG activity of the right LD was greater than the bilateral MT and ES in left return to neutral rotation with upper extremities in a fixed position, and the left LD was more active than bilateral MT and ES in right return to neutral rotation in the same fixed position. The EMG activity of the MT in all standing and quadruped return to neutral movements of spinal rotation was significantly less than the LD and ES. Lastly, in the standing position, the ES was significantly more active in both ipsilateral and contralateral return to neutral spinal rotation than bilateral LD and MT. Discussion/Conclusion: Our findings suggest that the LD significantly contributes to the return to neutral phase of spinal rotation in the quadruped position. The MT did not have a significant influence on the return to neutral phase of spinal rotation in any position, and the ES played a greater role in standing. Results of this study correlate with ongoing studies regarding the LD’s activation during the concentric phase of spinal rotation, and isometric lifting activities. Future research could include comparisons between healthy subjects and individuals who are experiencing low back pain. Clinical Relevance: This study assessed the contribution of the LD in comparison to the MT and ES during spinal rotation. Furthermore, this study particularly analyzed the LD activation and nearby musculature during the return to neutral phase of rotation. Our findings concluded that with fixed upper extremities the contralateral LD should be considered a major contributor during the return to neutral phase of spinal rotation with fixed upper extremities. Many activities throughout the day utilize spinal rotation with fixed upper extremities in the quadruped position, such as getting out of bed or up off the floor, supporting the statement that strength and mobility assessments of the LD should become a part of comprehensive evaluations by clinicians