existence of an optimum dynamic coefficient of friction and the influence on human gait variability

the existence of a range of optimal coefficient of friction that encompasses safety and comfort has not been addressed before. this paper assesses the existence of such a range and its relationship with the variability of human gait. six women walked for 15 min over five ceramic tile floorings with friction coefficients (dcof) ranging from 0.19 to 0.63. subjective opinions (pain, comfort, etc.) and biomechanical parameters including sagittal plane knee angle, tibia acceleration, and ground reaction forces were gathered. the required coefficient of friction (rcof) was calculated from ground reaction forces. the results show that as dcof increases so do reports of pain in the knees and under the metatarsal heads and toes; whereas a low dcof relates to pain in the thighs and perception of low friction. rcof showed a quadratic relationship with dcof indicating the existence of a range of optimal coefficient of friction outside of which walking strategy is modified either to avoid slipping (dcof < 0.25) or reduce pain (dcof > 0.55). this result is supported by the results of the analysis of gait variability using non-linear methods. floors inside the optimal range of friction yielded statistically significant higher entropy for tibia acceleration and knee angle, confirming the hypothesis that gait is more constrained outside that range (i.e. natural variability is reduced). relevance to the industry: floor friction is one of the main concerns for the floor industry and for decision makers when choosing public space paving (indoor and outdoor). the false concept ‘the more friction the better’ can induce manufacturers and technicians to make wrong decisions. this paper can assist the industry produce and select solutions encompassing safety and comfort.