Influence of body-shape-based mass scaling and thoracic disc stiffness on flexible-thorax model predictions of thoracolumbar loading during lateral bending
4 affiliations
- 1Department of Mechanical and Nuclear Engineering, Khalifa University of Science and Technology
- 2Department of Mechanical and Manufacturing Engineering, Ontario Tech University
- 3Institut für Biomechanik, Department of Health Sciences and Technology , ETH Zürich
- 4Department of Biomedical Engineering, Khalifa University of Science and Technology
Abstract
Accurate estimation of spinal joint and muscle forces is important for understanding spine biomechanics and informing rehabilitation and surgical planning. Conventional upper-body musculoskeletal (MSK) models often lack thoracic spine detail and use generalized mass distributions. This study developed a physiologically detailed thoracolumbar MSK model with a flexible thorax (FT), articulated ribcage, and thoracic intervertebral disc (IVD) stiffness profiles to improve force prediction during 30° lateral bending. Nineteen male subjects (10 normal-weight, 9 obese) were simulated using constant percentage-based (CPB) and body shape-based (BSB) mass scaling. An indirect comparison with IDP-derived reference compressive-force estimates was used to assess the physiological plausibility of FT model predictions. During left lateral bending, BSB scaling reduced RMSE from 11.35 to 6.91 % BW in normal-weight subjects and from 41.05 to 16.98 % BW in obese subjects, whereas during right lateral bending RMSE remained nearly unchanged in normal-weight subjects and increased in obese subjects. After Holm-Bonferroni correction, statistically significant differences (p < 0.05) between CPB and BSB models were observed in several joint and muscle force comparisons, particularly in obese subjects. Sensitivity analysis showed that compressive forces were highly dependent on thoracic disc stiffness, with interquartile range reaching 26.17 % BW at T12L1, whereas mediolateral shear forces varied by less than 2 % BW. These findings indicate that body-shape-based mass scaling and thoracic IVD rotational stiffness can substantially influence MSK-predicted spinal loads, particularly in obese subjects, and should be considered carefully when developing personalized thoracolumbar models.
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BibTeX
@article{abdullah2026influence,
title = {{Influence of body-shape-based mass scaling and thoracic disc stiffness on flexible-thorax model predictions of thoracolumbar loading during lateral bending}},
author = {Muhammad Abdullah and Abdul Aziz Hulleck and Tao Liu and Dominika Ignasiak and Kinda Khalaf and Marwan El-Rich},
journal = {Scientific Reports},
year = {2026},
month = jul,
doi = {10.1038/s41598-026-61797-9},
url = {https://doi.org/10.1038/s41598-026-61797-9},
note = {CC BY},
}
RIS
TY - JOUR
TI - Influence of body-shape-based mass scaling and thoracic disc stiffness on flexible-thorax model predictions of thoracolumbar loading during lateral bending
AU - Muhammad Abdullah
AU - Abdul Aziz Hulleck
AU - Tao Liu
AU - Dominika Ignasiak
AU - Kinda Khalaf
AU - Marwan El-Rich
PY - 2026
DA - 2026/07/01
JO - Scientific Reports
DO - 10.1038/s41598-026-61797-9
UR - https://doi.org/10.1038/s41598-026-61797-9
AB - Accurate estimation of spinal joint and muscle forces is important for understanding spine biomechanics and informing rehabilitation and surgical planning. Conventional upper-body musculoskeletal (MSK) models often lack thoracic spine detail and use generalized mass distributions. This study developed a physiologically detailed thoracolumbar MSK model with a flexible thorax (FT), articulated ribcage, and thoracic intervertebral disc (IVD) stiffness profiles to improve force prediction during 30° lateral bending. Nineteen male subjects (10 normal-weight, 9 obese) were simulated using constant percentage-based (CPB) and body shape-based (BSB) mass scaling. An indirect comparison with IDP-derived reference compressive-force estimates was used to assess the physiological plausibility of FT model predictions. During left lateral bending, BSB scaling reduced RMSE from 11.35 to 6.91 % BW in normal-weight subjects and from 41.05 to 16.98 % BW in obese subjects, whereas during right lateral bending RMSE remained nearly unchanged in normal-weight subjects and increased in obese subjects. After Holm-Bonferroni correction, statistically significant differences (p < 0.05) between CPB and BSB models were observed in several joint and muscle force comparisons, particularly in obese subjects. Sensitivity analysis showed that compressive forces were highly dependent on thoracic disc stiffness, with interquartile range reaching 26.17 % BW at T12L1, whereas mediolateral shear forces varied by less than 2 % BW. These findings indicate that body-shape-based mass scaling and thoracic IVD rotational stiffness can substantially influence MSK-predicted spinal loads, particularly in obese subjects, and should be considered carefully when developing personalized thoracolumbar models.
SN - 2045-2322
ER -