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Slipping and falling on ascent and descent stairs often lead to high risk of injuries and fatalities. In this paper, factorial analysis was used to study various factors influential to the biomechanics, such as ground reaction force (GRF) and required coefficient of friction (RCOF). The purpose of this study is to investigate the effect of the factors, such as stairs, climbing style, climbing mode and participants on vertical GRF and RCOFs. Ten healthy younger adults were asked to perform two replicates of each trial under twelve different conditions (two climbing modes: Ascent and decent; three different stair heights: 0.165 m, 0.173 m and 0.178 m; two climbing styles: Walking and running). Force platform was used to measure both vertical and horizontal GRF. In addition, participant's body weight, stature and average time spent on each condition were recorded. Analysis of variance (ANOVA) results indicated that the effect of climbing mode, climbing style and participants on vertical GRF were significant. Descending requires more vertical GRF than ascending while running requires more vertical GRF than walking. The possible reason of increasing vertical GRF may be explained by increasing gait speed as well as whole body momentum. Compared with vertical GRF, only climbing mode and style show significant effects on RCOFs. RCOF during foot landing (RCOF FL ) is larger than RCOF during pushoff (RCOF PO ) for stair descent and ascent while both RCOF FL and RCOF PO of running are higher than walking. These results indicate that running is not recommended when descending, as it requires highest vertical GRF as well as RCOFs during stair climbing. In the future study, more female participants and force platforms can be used to study the effect of gender and position of steps on GRF and RCOFs during complete cycle of stair descending and ascending. In addition, different stair heights with same stair total length may be selected to identify effect of stair height on biomechanics.

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