Assessment of shoe-floor slipperiness with respect to contact-time-related variation in friction during heel strike

The variation in utilized and available friction over shoe-floor contact time was determined in the presence of high- and low-viscosity contaminants. The objectives were to improve the validity of slipperiness evaluations and to find better criteria for safe friction during heel strike. The utilized friction coefficients for six shoe types were determined during gait-trials with male participants. The available friction coefficients of these shoes were measured with a test rig simulating heel slipping. The experiments were performed on a stainless steel floor with concentrated glycerol ('oily' condition) and diluted glycerol (1:10 in water) as contaminants. It was hypothesized that any single friction measurement criterion would be an insufficient predictor for safe gait with no slip or with slip recovery, not leading to a fall. The results showed that both transitional friction (time-intervals from zero to about 250 ms of heel contact) and steady state kinetic friction (time-intervals from about 250 ms to 450 ms) properties in the shoe and floor interface play an important role in slipperiness measurement and slip/fall risk assessment. The role of static friction in the risk assessment remained unclear.