Exercise-specific mechanical stimuli are associated with regional lumbar bone adaptation: A combined in vivo and in silico multi-scale study

Background Exercise is widely recommended to maintain lumbar bone mineral density (BMD), the tissue-level mechanical environment generated within the lumbar spine during different exercises remains difficult to assess in vivo. This study integrated individualized musculoskeletal modelling, finite element analysis, and longitudinal quantitative computed tomography (QCT) to characterise exercise-specific lumbar loading patterns and interpret them alongside regional BMD adaptation. Methods Ten postmenopausal women with low BMD who completed a 6-month combined exercise intervention were included (ChiCTR2400081574). QCT scans were acquired at baseline and follow-up to quantify BMD changes in the vertebral body (VB) and posterior region (PR). Individualized musculoskeletal models of walking, heel drops, jumping, and resistance exercise were developed to estimate joint reaction forces and muscle forces. These loads were transferred to individualized lumbar finite element models using a MATLAB–Python workflow to calculate segmental and regional von Mises stresses. Statistical analysis was performed using one-way ANOVA, with p < 0.05 considered statistically significant. Results Longitudinal QCT revealed that BMD was preserved or increased in the VB, whereas BMD declined in the PR, particularly at L1–L3. Jumping produced the highest peak joint reaction forces and von Mises stresses in the superior lumbar segments, whereas resistance exercise generated the greatest loading at L4–L5. Across all tasks and vertebral levels, von Mises stresses were consistently higher in the VB than in the PR. Conclusions Distinct exercise modalities generated different segmental and regional loading environments within the lumbar spine. These mechanical patterns were broadly consistent with the observed regional BMD changes, providing a mechanically informed interpretation of lumbar bone adaptation during exercise. Trial registration: Chinese Clinical Trial Registry, ChiCTR2400081574 (retrospectively registered 5 March 2024).