Kinematics and kinetics of the shoe during unexpected ladder slip events

Foot slipping is a common initiating event in ladder falls, often leading to severe injuries. Methods for measuring the slipperiness of rungs are impeded by a lack of data on slip events during climbing. This study investigated the kinematics and kinetics of ladder slip events to guide coefficient of friction test methods for ladder rungs. Eighty-eight participants (45F, 43 M; 43.4 ± 12.3 yrs; 80.1 ± 16.9 kg; 170.9 ± 91.6 cm) climbed a series of ladder configurations with differing rung designs and ladder angles in a randomized order. A liquid contaminant (90 % glycerol +10 % water by volume) was applied during each participant's final trial and the responses were categorized into slip and non-slip events with a cluster analysis and reviewer classification. A total of 11 slipping events (9 forward and 2 backward slips) were identified from 102 ladder climbs based upon their peak slipping speeds and slip distances. Slipping speed, shoe-rung angle, transverse foot angle, normal force, shear force, anterior-posterior (AP) foot position, and medio-lateral (ML) foot position were quantified at the start of slip and at the peak slipping speed for forward slips with mean values and 95 % confidence intervals reported. Slips had speeds of 0.34 m/s at their peak, with normal forces around 460 N. We argue the need for testing conditions informed by the under-shoe conditions observed in this study: forward slipping (8° dorsiflexion, 0.34 m/s, 400 N).