Investigating Foot-sock Friction: A Comparison of Two Different Methodologies

Abstract

Two different methodologies for assessing the friction between plantar skin and sock textiles are compared in this study. The first approach uses a custom-built friction plate rig. The rig consists of sock material mounted on a test plate attached to two load cells that measure normal and shear loads at the skin-sock textile interface. With this methodology, participants are required to slide their foot over the test plate whilst maintaining a targeted normal load and a relatively consistent sliding speed. The second approach uses a pneumatically-driven foot probe loading device. The device includes an instrumented probe with sock material on its contact surface. Participants are instructed to stand on a platform whilst the probe is applied to, and then driven across, the plantar aspect of foot. The cyclic motion of the probe is displacement-controlled and normal and shear loads are measured using load cells. Both approaches allow friction coefficients to be calculated from load data collected during the sliding phase of movement. Data from both approaches was examined, collected from friction tests using the same six participants and sliding contact between the first metatarsal head (1MTH) region and textiles from two commercially available running socks. Both approaches were capable of measuring the friction between 1MTH skin and sock materials and good agreement was found between them. In the dry conditions tested, the cotton-rich sock was found to provide lower friction that the anti-blister sock material.