Distribution of the local required coefficient of friction in the shoe–floor contact area during straight walking: A pilot study

We developed a shoe mounted with miniature tri-axial force sensors and investigated the distribution of the local required coefficient of friction (RCOF) in the contact area between the shoe sole and floor during straight walking. Four miniature force sensors were mounted on the outsole of the shoe. The study comprised five healthy young adult males (mean age: 22.4 years). Participants were instructed to walk straight at a normal pace on a level resin floor under 25 different sensor layouts to measure the three-directional ground reaction forces (GRFs) at 52 local positions in the region of the shoe sole. The local RCOF value (the maximum peak value of the ratio of the horizontal GRF to vertical GRF) was calculated at each sensor position. The mean local RCOF values at ten local positions were observed to be >0.4, whereas those at the lateral rear foot and toe were observed to be >0.6. These local RCOF values were much higher than the mean RCOF values calculated from the resultant local GRFs (0.18). The results of the present study will provide information on the distribution of friction requirements and the direction of applied horizontal GRF will aid in the development of slip-resistant shoe sole patterns.