Author(s): HOGAN, J.1,2, BUNCLARK, H.2, PICKESS, H.2, BYRNE, C.2, BROWN, P.3, FALLOWFIELD, J.4, POWELL, S.1, ALLSOPP, A.1, DIXON, S.2, Institution: EXETER UNIVERSITY , Country: UNITED KINGDOM, Abstract-ID: 2456

INTRODUCTION:
Accurate quantification of lower limb mechanical loading is critical for understanding bone strain and injury risk during military training activities. Laboratory-based force plates (FP) provide high-fidelity measurements but lack ecological validity for field-based activities.1 Force-measuring insoles (Insoles) offer a practical alternative; however, their validity across the speeds and external loads typical of military training remains insufficiently established. This study aimed to validate force-measuring insoles for the assessment of bone-relevant loading variables during military-relevant movements – with and without load carriage.
METHODS:
Ten healthy males walked (1.5 m·s⁻¹ ± 5%) and jogged (3.6 m·s⁻¹ ± 5%) under external load (0, 20, and 40 kg) across a raised runway. Ground Reaction Force (GRF) data were collected simultaneously using a FP (criterion measure: 1000 Hz) and Insoles (200 Hz). Ten successful, synchronised steps were recorded per participant per condition. Variables of interest included peak GRF, loading rate, impulse, and stance time. Paired samples t-tests were used to assess systematic bias between measures. Reliability and agreement were assessed using intraclass correlation coefficients (ICC) and Bland–Altman (mean bias and 95% limits of agreement [LoA]) analyses, respectively.2 Statistical significance was set at p < 0.05. A mean bias of ±5% was considered acceptable agreement between measures.
RESULTS:
Across conditions, peak force was significantly higher (p = 0.0011), and stance was significantly shorter (p < 0.001) in the Insoles conditions. There were no statistically significant differences for loading rate or impulse (p > 0.05). For all measures, Insoles demonstrated excellent reliability with the FP (ICC = 0.905–0.997). Systematic bias was 50.0 ± 282.8 N (equating to 3 ± 18%) for peak GRF, -37.3 ± 3602 N·s-1 (equating to -1 ± 35%) for loading rate, 4.2 ± 75.8 N·s (equating to 1 ± 16%) for impulse and -0.01 ± 0.03 s (equating to -1 ± 5%) for stance time.
CONCLUSION:
Despite some statistically significant differences between Insoles and FP, reliability data demonstrate that Insoles provide a valid, field-expedient measure of mechanical loading for military-relevant activities within expected exposure ranges. However, caution is advised when interpreting data from Insoles due to wide LoA, particularly during higher-force movements (e.g., jogging).
1: Verheul et al., 2020;
2: Kotner et al., 2011.