Running is a highly dynamic locomotion process, yet most existing aerodynamic studies approximate the runner using a single static posture. This study presents a validated computational fluid dynamics investigation of posture-dependent running aerodynamics throughout the gait cycle from a quasi-static perspective. Five representative gait-cycle postures are analysed for a male runner. The results reveal substantial aerodynamic variations throughout the gait cycle with maximum drag occurring for the mid-stance and minimum drag for the flight postures. Relative to the minimum-drag posture, the peak drag area increases by approximately 20.6%. Flow-field analysis shows that changes in leg configuration strongly influence wake development. The toe-off and flight postures are characterised by a partially interrupted torso wake and more compact wake structures, whereas the higher-drag postures exhibit broader low-velocity wake regions. Body-part decomposition further indicates that the torso is the dominant drag contributor, accounting for approximately 50–59% of the total drag area, while the upper legs exhibit the strongest posture sensitivity. The findings provide new physical insights into posture-dependent running aerodynamics and establish a foundation for future investigations of fully dynamic running motion.
Finite element (FE) modelling is a powerful tool for investigating spinal biomechanics. Subject-specific finite element models of the spine are commonly built from supine data obtained from CT images, with harmful radiation and without soft-tissue structures. However, a more accurate evaluation of vertebrae and intervertebral disc loading requires the analysis of the subject in upright posture. In this study we propose a radiation-free alternative to create subject-specific standing FE models by combining supine MRI with ultrasound-based 3D spinal curvature assessment in standing posture. Subject-specific supine FE models of T3-L5 were created from synthetic CT (AI-generated from MRI) of 8 children. Dedicated spinal ultrasound was used to detect the positions of the vertebral laminae, which were used as input to convert the FE model from supine to standing. RMSE was found within 1 mm for the fitted vertebral levels. Validation against conventional radiographic measurements showed no statistical difference in sagittal alignment between the two imaging modalities in the lumbar and mid-to-lower thoracic parameters. In addition, the distance between the vertebral centroids measured from radiographs and from the upright FE model in sagittal and coronal plane was found to be less than 6 mm for the fitted levels. In conclusion, we demonstrate the feasibility of using completely radiation-free imaging as an alternative to CT and bi-planar X-ray to build subject-specific, upright, detailed FE models.
