The impact of a systematic reduction in shoe-floor friction on heel contact walking kinematics-- A gait simulation approach.

Falls initiated by slips and trips are a serious health hazard to older adults. Experimental studies have provided important descriptions of postural responses to slipping, but it is difficult to determine why some slips result in falls from experiments alone. Computational modeling and simulation techniques can complement experimental approaches by identifying causes of failed recovery attempts. The purpose of this study was to develop a method to determine the impact of a systematic reduction in the foot-floor friction coefficient (mu) on the kinematics of walking shortly after heel contact (approximately 200 s). A walking model that included foot-floor interactions was utilized to find the set of moments that best tracked the joint angles and measured ground reaction forces obtained from a non-slipping (dry) trial. A "passive" slip was simulated by driving the model with the joint-moments from the dry simulation and by reducing mu. Slip simulations with values of mu greater than the subject-specific peak required coefficient of friction (RCOF), an experimental measure of slip-resistant gait, resulted in only minor deviations in gait kinematics from the dry condition. In contrast, slip simulations run in environments characterized by mu<peak RCOF resulted in body kinematics that were substantially different from normal/dry gait patterns, more specifically greater knee extension and hip flexion angles were observed in the slip simulations. These findings imply the need for early and appropriate active corrective responses to prevent a fall in environments with mu values less than the peak RCOF.