Effects of Midsole Hardness and Insole Materials on Shock Absorption in Protective Boots

This study aimed to determine the influence of varying midsole hardness and insole materials on cushioning performance of protective boots. Twenty healthy male participants performed running tests with six conditions of protective boots, varying in midsole hardness (50 shore C-soft, 60 shore C-medium, 70 shore C-hard) and insole material (Thermoplastic Polyurethane, Polyurethane). The first peak vertical ground reaction force (1st PVGRF), impact duration (ID), and average vertical loading rate (AVLR) were measured by a force plate. The subjective cushioning evaluation was also conducted using a visual analogue scale. The results showed that midsole hardness had a significant effect on ID (P = 0.048, η²p = 0.151) and AVLR (P = 0.048, η²p = 0.301) but not on 1st PVGRF (P = 0.222, η²p = 0.076). The ID was longer and the AVLR was lower for hard shoes compared to soft shoes. Insole materials had no significant effect on any of the impact variables (P > 0.05). Subjective evaluations indicated that the medium-hardness shoes received the highest cushioning scores among the three hardness levels. The findings suggest that midsole hardness influences impact duration and loading rate, while insole materials do not significantly affect the shock absorption performance of protective boots.