The Influence of Footwear Sole Hardness on Slip Initiation in Young Adults*

Abstract

Slips occur when the friction demand of an individual exceeds the friction available from the shoe/floor interface. Shoe sole hardness is one of the factors thought to influence friction demand and available friction. The purpose of this study was to determine the influence of footwear sole hardness on the probability of slip initiation. Forty young adults were randomized into a hard or soft sole group. Slip events during the slippery floor trials were documented using a motion analysis system. The proportion of slip events in the hard sole group was greater than that in the soft sole group. The difference between utilized and available friction accurately predicted 90% of slip outcomes. Our data support the premise that individuals wearing shoes with harder soles are at greater risk for slipping. The results of this study suggest that shoe sole hardness should be considered when designing footwear aimed at decreasing slip risk.

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

“…This would suggest that once the available friction from a floor surface is decreased (i.e., in the presence of a contaminant), the observed reduction in friction demand resulting from gait modifications when wearing hard soles shoes may not be sufficient to prevent a slip from occurring. This hypothesis is consistent with a recent publication by Tsai and Powers [23] who demonstrated that persons wearing hard soled shoes are more likely to experience a slip event when compared to persons wearing soft soled shoes.…”

A Microscopic Finite Element Model of Shoe–Floor Hysteresis and Adhesion Friction

“…Nosonovsky and Mortazavi [47] explained that materials selforganize to different steady-state roughness values dependent on their material properties and the counter surface that is causing the wear. Previous work that has attempted to describe the effects of shoe material properties on shoefloor friction has led to conclusions that softer shoe materials lead to larger lubricated or hysteresis friction [12,[48][49][50][51]. The model used in this study reveals that the increased hysteresis friction for softer shoe materials is likely due to the fact that softer materials typically have higher roughness [47,[50][51][52].…”

The influence of heel height on utilized coefficient of friction during walking

“…To avoid spuriously high uCOF values resulting from division by small numbers [1,13,14] only data after the first 5% of the stance phase was considered for analysis. We felt that this criteria was justifiable as slips typically occur near the end of weight acceptance (i.e.50-100 ms following initial contact) [15][16][17].…”