Dynamic finite element analysis of internal tibial mechanical responses during drop jumps: The ability of external measures to represent internal bone loading.

OBJECTIVE: To investigate the internal mechanical response of the tibial shaft region of interest (ROI) during the landing-to-take-off phase of drop jumps (DJs) performed from different drop heights using musculoskeletal modeling and dynamic finite element analysis (FEA), and to examine the relationship between external and internal loading. METHODS: Seventeen healthy strength-trained males performed DJs from seven heights (30-90 cm). Kinematics, vertical ground reaction force (vGRF), and surface electromyography were collected synchronously. OpenSim combined with CEINMS was used to estimate dynamic muscle forces, which were applied to subject-specific dynamic finite element models of the tibia and fibula. P95 MaxP-stress, P95 MaxP-strain, P5 MinP-stress, P5 MinP-strain, P95 vM-strain, high-strain volume (HSV) above 3000 με, and HSV Percent were extracted within the ROI. SPM1D, repeated-measures statistics, and correlation analyses were performed. RESULTS: From 30 to 90 cm, peak P95 vM-strain increased from 1558.68 ± 105.80 to 2915.54 ± 148.86 με, HSV increased from 1278.59 ± 375.81 to 6599.91 ± 1205.36 mm³, and peak P5 MinP-stress changed from -21.83 ± 3.84 to -44.39 ± 2.99 MPa (p < 0.001;ηp2 = 0.313-0.448). P95 MaxP-strain and P5 MinP-strain also differed significantly across heights (p < 0.001), whereas P95 MaxP-stress did not (p = 0.16). Time-series differences occurred mainly during the early-to-middle portion of the landing-to-take-off phase. Peak vGRF was correlated with peak P95 vM-strain at 30-70 cm (R = 0.728-0.959, p ≤ 0.011), but not at 80-90 cm (p ≥ 0.153). CONCLUSIONS: Experimentally measured peak vGRF and FE-derived tissue-level variables provide complementary information regarding tibial mechanical loading during DJs. The findings support the interpretation of relative tibial loading differences among drop-height conditions but should not be regarded as direct evidence for an optimal DJ height.