Early Heelstrike Kinetics Are Indicative of Slip Potential During Walking Over a Contaminated Surface

OBJECTIVE The objective of this study is to examine ground kinetics early in stance while walking on a contaminated surface and assess the potential of kinetics to quantify risk of slipping. BACKGROUND Prior studies of slipping have dismissed early ground kinetic data,and therefore no prior literature has been able to assess the viability of using these data to quantify slip potential. METHOD A total of 11 healthy male participants volunteered to walk over a force plate that was at random times contaminated with soap.Ground kinetics were measured by the force plate (2400 Hz), and heel displacement was quantified using high-speed video cameras (240 Hz) and retro-reflective markers. RESULTS The results indicated a significant reduction in shear force as early as 0.42 ms after heelstrike for contaminated trials, whereas for utilized coefficient of friction, a significant reduction was not seen until 11.34 ms. Heel displacements considered "safe" in the literature (< 30 mm) demonstrated proportionally different thresholds for shear force and utilized coefficient of friction. CONCLUSION The authors suggest that shear force in early stance shows more promise in quantifying slip potential as compared to utilized coefficient of friction given that (a) significant differences are seen earlier in shear than utilized coefficient of friction and (b) the threshold for utilized coefficient of friction, over which heel displacement stabilized to a"safe" value, exceeded values for utilized coefficient of friction that have been recommended as "safe". APPLICATION These results have wide implications for standards related to the design and testing of interventions to prevent injuries because of slipping.