Optimum Insole Hardness for Attenuating Peak Plantar Pressure Under Simulated Loading Scenarios

To provide optimal cushioning capacity, an in-depth understanding of the biomechanical interactions between the foot and therapeutic insoles is mandatory. The goal of this study was to quantify the hardness of plantar soft tissues (PSTs) and investigate the potential association between the hardness of PSTs and the optimum hardness of insole materials. The authors tested the hardness of PSTs in eight plantar regions by using a durometer to examine 30 cadaveric feet. The effects of hardness and loading magnitude on peak plantar pressure at the heel–insole interface were investigated in simulated weight-bearing tests. Significant effects of insole hardness on the cushioning capacity were observed among different loading conditions (p<0.01). No significant association was found between the hardness of individual-specific PSTs and optimum cushioning materials (p<0.05). This study provides quantitative data on PST hardness, and this knowledge may be valuable for developing insole materials with similar hardness to the PST in order to achieve optimum pressure relief under the foot.