Influence of age and gender on utilized coefficient of friction during walking at different speeds

A frequently cited theory suggests that ratio of leg length and stride length (i.e., normalized stride length) can be used to predict the utilized coefficient of friction (COF) during walking. As stride length and leg length differs across persons of different ages and genders, it is probable that utilized COF values also will vary. The purpose of this study was to evaluate the influence of age and gender on utilized COF during non-slip pedestrian gait. Sixty healthy adults were divided into three groups by age (10 males and 10 females in each age group): Young (20-39 y.o.); Middle-aged (40-59 y.o.); and Senior (60-79 y.o.). Ground reaction forces (AMTI forceplate; 600 Hz.) were recorded as subjects walked at slow, medium, and fast speeds. Utilized COF throughout stance was calculated as the ratio of the resultant shear force and vertical force. When collapsed across are groups, females generated higher peak utilized COF values than males at the slow walking speed (μ = .24 vs. μ = .20), while males generated higher peak utilized COF values than females at the fast walking speed (μ = .28 vs. μ = .24). When collapsed between genders, middle-aged subjects generated higher peak utilized COF values at the medium speed than both young and senior subjects (μ = .26 vs. μ = .22 and μ = .22, respectively). At the fast speed, middle-aged subjects generated higher peak utilized COF values than senior subjects (μ = .29 vs. μ = .23). No gender or age related differences in normalized stride length were found. Normalized stride length was a significant predictor of utilized COF, however, only 18% of the variance in utilized COF values could be explained by this factor. These data suggest that while age and gender differences in utilized COF exist, the basis for these differences can not be explained by normalized stride length alone.