Reliability device for measuring frictional resistance between footwear sole and contact surface

The measurement of frictional resistance between footwear and a surface is challenging, with great variability observed between measurements. This study attempted to evaluate the reliability of a device designed for measuring the frictional resistance between the sole of a shoe and the surface during a simulated cutting movement. A device was constructed to measure the frictional resistances of different soccer shoes on a surface. A load cell was used for the kinetic data, and a three-dimensional motion measurement system was used to perform a kinematic analysis. Specific parameters of the torque curve versus the rotation angle were extracted and calculated, including the peak torque, stiffness, and area under the torque curve. To examine the reliability, the intraclass correlation coefficient (ICC), standard error of measurement (SEM), minimal detectable change (MDC), and root mean square (RMS) indices were used. The reliability of successive measurements was investigated on the same day and 1 week later. For all variables analyzed, the ICC was high (>0.9), with low SEM, MDC, and RMS values. The device could reliably measure the frictional resistance between different soccer shoes and the surface. Peak torque, stiffness, and area under the torque curve were recommended as the primary measures to be considered in future studies. Moreover, this study provides an index for the reproducibility of frictional resistance between sessions, which has not been previously reported. This information can be used by the shoe industry to design new shoes.