Abstract
<title>Abstract</title> <p>Interchangeable distal components may provide a practical means of modifying the mechanical response of a running prosthetic foot (RPF) without replacing its primary carbon-fibre structure. However, the influence of midsole geometry on RPF behaviour remains poorly quantified. This exploratory study assessed whether interchangeable midsole inserts could modify selected mechanical descriptors of a single C-shaped RPF under controlled mid-stance-inspired bench-test conditions and whether a simplified finite element (FE) model could reproduce the observed trends. The RPF was tested in a No-midsole control configuration and with three EVA midsole inserts of different geometry, while retaining the same spiked outsole. A quasi-static vertical compression of 110 mm was applied with the ground plate free to translate horizontally and the horizontal force controlled close to zero. The response was characterised using elastic energy-equivalent stiffness (Keq), Stiffening Ratio (SR), Biaxiality Ratio (BR), and centre of pressure (CoP) trajectory. Relative to the control, M01 and M02 increased by 24% and 28%, respectively, whereas M03 reduced it by 13%. All inserts reduced SR, while BR changed only modestly. CoP trajectories showed configuration-dependent differences in the progression of the resultant ground reaction force. The FE models reproduced the direction of the experimental changes in Keq, with normalised force–displacement RMSE values between 0.82% and 2.18%, whereas larger discrepancies were observed for SR. These findings suggest that midsole geometry may influence the bench-test response of the tested RPF and that simplified FE models may support preliminary comparison of global response trends.</p>