Relationship Between Thoracic Flexibility and Spinal Curvature During Trunk Extension in Healthy Adults

Background: Non-specific lower back pain is a common medically and economically impactful condition that affects patients’ quality of life. Purpose: This study aimed to determine the relationship between thoracic expansion and spinal curvature angle during trunk extension in healthy participants. Results: The participants comprised 24 men aged 18–21 years. The measurement items included the lateral and longitudinal diameters of the thorax, measured at the level of the xiphoid process and 10th rib, and spinal curvature angle, measured in the upright posture and trunk extension position. The difference in thoracic expansion levels during trunk extension tended to be greater in the lower thorax than in the upper thorax, with the lateral diameter higher than the longitudinal diameter. The inferior thoracic and lumbar curvatures increased with trunk extension. Regarding the relationship between the difference in thoracic expansion and the amount of change in the spinal curvature, the difference in the expiratory lateral diameter of the lower thorax during trunk extension was positively correlated with the superior thoracic curvature during trunk extension. Conclusions: These results indicate that expansion of the lower thoracic lateral diameter increased the thoracic curvature during trunk extension exercises. Consequently, the lumbar curvature may be suppressed. Reduced lower thorax flexibility may enhance lumbar curvature during trunk extension. Therefore, flexibility of the lower lateral thoracic diameter may be a factor when preventing lower back pain. KEY WORDS: Thorax, Lateral Diameter, Longitudinal Diameter, Trunk Extension, Chest Griping.