Analysis of required coefficient of friction in running and walking.

The popularity of running has increased over the past few years. However, just a few studies in running have focused on the friction between surface and shoe/foot. Changes in friction can affect aspects of human motion, such as safety, motion pattern and efficiency among others. The aim was to investigate the effects of cadence (walk, self-selected running and imposed-running), stance sub-phases (absorption and propulsion) and footwear (barefoot and shod) on the required coefficient of friction (RCOF) of regular runners. Twenty healthy runners (12 males, 8 females, 29.4 ± 4.9 years, 70.4 ± 9.6 kg) participated in this study. Two force plates were used to measure the ground reaction forces (GRF) in order to calculate the RCOF for each condition and the stance phase was divided in sub-phases. In walk, the RCOF was smaller in the absorption than in propulsion phase ( < 0.001). Results evidenced effects of the cadence ( < 0.001), stance sub-phases ( < 0.001) and footwear ( < 0.001) on the RCOF. There was interaction effect in cadence with stance sub-phases ( < 0.001) and footwear with stance sub-phases ( < 0.001). Our results show RCOF is influenced by cadence and footwear condition in the absorption phase.