The effect of shoe material on the kinetics and kinematics of foot slip at impact on concrete.

Previous studies on shoeing have demonstrated that shoe material alters the time taken from foot impact to the foot stopping sliding (slip time) and the distance slid. These are assumed to reflect differences in the craniocaudal ground reaction force (GRF) between the shoe and the ground during foot slip. This study tested the hypothesis that the slip time and distance are reflected in the resistance to slippage of the foot after impact. The forefeet of 8 horses were shod in horseshoes constructed of steel, plastic and rubber. Each horse was trotted for 8 placements per forefoot in each shoe type over a concrete topped forceplate and simultaneous kinematic data recorded at 240 Hz. Slip distance and slip time were calculated from the kinematic data and craniocaudal (Fy), and vertical (Fz) GRFs determined during slip the averaged for each shoe type. The slip time and distance were variable between runs in all 3 shoe types, and there was no significant difference between the mean values for the 3 shoe types. Fy reached a value of 0.98 +/- 0.17 N/kg during slip in the plastic shoes which was significantly lower than the rubber shoes, at 1.13 +/- 0.17 N/kg, P = 0.02. The Fy/Fz ratio (a measure of dynamic friction) was significantly lower in the plastic shoes, 0.34 +/- 0.08, compared to the steel shoes, 0.46 +/- 0.04, P = 0.003. This study is being extended to investigate effects of shoe slippage at the end of the stance phase and the energy dissipation during foot slip in the different shoe types. Future investigations should aim to identify the optimum slip characteristics to modulate loading (magnitude and rate) during impact, with the aim of reducing the risk of injury.