Biomechanical effects of insole material stiffness on the human foot: a finite element analysis

Functional insoles are widely used to redistribute plantar pressure and support the medial arch; however, the biomechanical effects of insole material stiffness remain unclear. This study employed finite element analysis (FEA) to investigate the relationship between insole stiffness and foot tissue loading, providing a theoretical basis for personalized insole design and clinical application. A three-dimensional finite element model of a healthy 26‑year‑old male foot and insole was reconstructed from CT images. Exploring the trend of the insole material stiffness on foot biomechanics through parametric analysis. Six insole materials with elastic moduli of 100, 260, 1,000, 3,000, 5,000, and 500,000 MPa-were analyzed, The Poisson's ratio for all insole materials was assumed to be 0.45. Two loading conditions, static bilateral stance and gait forefoot contact, were simulated to evaluate foot displacement, plantar stress, and stresses on the medial process of the calcaneal tuberosity and metatarsals. The finite element model demonstrated good agreement with experimental plantar pressure measurements, the experimentally measured peak plantar pressure was 0.2217 MPa, while the finite element model calculated a value of 0.234 MPa, with a relative error of approximately 2%. Both high-stress regions were located at the central area of the heel, and the stress distribution trends were consistent, indicating that the model validation is effective. Increasing insole stiffness reduced foot displacement (48.0%), plantar peak stress (47.5%), calcaneal peak stress (30.8%), and metatarsal peak stress (20.8%). When the elastic modulus exceeded approximately 3,000 MPa, further biomechanical benefits plateaued, indicating a diminishing marginal effect. This study quantitatively characterizes the intrinsic relationship between insole stiffness and foot biomechanics under static and dynamic conditions. The findings provide robust biomechanical evidence to guide personalized insole design, prevent soft tissue overload, and support the clinical application of functional insoles.