Impact Of Muscle Stiffness On Sagittal Spinal Alignment In Healthy Young Men

Spinal posture impacts core stability and movement, which in turn influences sports performance and injury prevention. Understanding how muscle stiffness affects spinal alignments could lead to enhance sports performance and reduce injury risk. PURPOSE: To examine which muscle stiffness affect thoracic and lumbar spinal sagittal angles. METHODS: Twenty-seven healthy young men participated in this study. Thoracic and lumbar spine sagittal angles were measured in a seated position using the Spinal Mouse, with positive values indicating flexion and negative values indicating extension. Muscle stiffness were measured via ultrasound shear wave elastography, focusing on the pectoralis minor, pectoralis major (upper, middle, and lower fibers), and trapezius (upper, middle, and lower fibers). Shear moduli values were used to assess muscle stiffness. Multiple regression analysis was conducted to identify impact of muscle stiffness on sagittal spinal alignment. RESULTS: Average thoracic and lumbar spine sagittal angles were 32.3 ± 9.4° and 0.0 ± 10.1°, respectively. The multiple stepwise regression analysis identified middle trapezius as independent determinant of thoracic spine sagittal angle (R2 = 0.091, p < 0.05, β = -0.302). Additionally, the multiple stepwise regression analysis showed middle trapezius and upper pectoralis major as independent determinants of lumbar spine sagittal angle (R2 = 0.150, p < 0.05, β = 0.271, β = -0.269, respectively). CONCLUSIONS: These results suggest that stiffness of the middle trapezius and upper pectoralis major are related to thoracic and lumbar spinal sagittal angles. Specifically, individuals with greater thoracic flexion tend to have softer middle trapezius, while those with more lumbar flexion tend to have stiffer middle trapezius and softer upper pectoralis major. However, the effect of muscle stiffness on posture appears limited, and other factors are likely involved. Further research is needed to clarify these relationships.