Increased shoe sole hardness results in compensatory changes in the utilized coefficient of friction during walking

Based on mechanical testing, harder soled shoes have been shown to provide less available friction than soft soled shoes. Whether or not humans adjust their utilized coefficient of friction (COFu) and gait kinematics to accommodate the decrease in available friction while wearing hard soled shoes is not known. Fifty-six young adults participated in this study. Ground reaction forces, full body kinematics, stride characteristics and subjective perception of footwear slipperiness were recorded under both hard and soft soled shoe conditions. Paired t-tests were used to identify the differences between two shoes conditions. Results indicated that the peak COFu was significantly less when wearing the hard soled shoes compared to when wearing the soft soled shoes (0.23 vs. 0.26, P<0.001). The decrease in peak COFu was the result of a decrease in the resultant shear forces at the time of peak COFu as no difference in the vertical ground reaction forces was observed. When wearing hard soled shoes, subjects demonstrated decreased total body center of mass (COM) acceleration prior to and immediately following initial contact, decreased walking velocity, shortened stride length, and reduced ankle dorsiflexion angle at initial contact. Taken together, we believe that these gait modifications represent behavioral adaptations to wearing shoes that are perceived to be more slippery.