During roof-to ladder transitions, walk-through extensions modify required friction direction

Abstract

Severe and fatal falls involving ladders commonly occur during transitions across the ladder and another support surface. Slipping is a common initiating event in ladder falls. This study characterized the friction requirements and body kinematics of descending roof-to-ladder transitions with and without a walk-through extension. Healthy adults who regularly climb ladders (n = 17) completed descending roof-to-ladder transitions, while foot-rung kinetics and body kinematics were recorded. The peak required coefficient of friction (RCOF) with respect to the plane of the shoe sole was calculated. The RCOF and body angle were calculated using their resultant values and projections in the frontal and sagittal planes. Foot angle was calculated in the sagittal plane. Repeated-measures ANOVA determined that compared to a walk-through ladder, a traditional ladder was associated with a higher RCOF in the medial–lateral (ML) direction (F1,16 = 190.07, p < 0.001) and a lower RCOF in the anterior-posterior (AP) direction (F1,16 = 11.02, p = 0.004), but had no significant relationship with the resultant RCOF (F1,16 = 0.098, p = 0.76). Spearman’s rho tests performed across all testing configurations identified significant associations between foot angle and overall RCOF (rs = −0.724, p < 0.001), foot angle and AP RCOF (rs = −0.871, p < 0.001), and frontal plane body angle and ML RCOF (rs = 0.782, p < 0.001). Clustering in the data suggests that ladder attachments reduced frontal plane kinematics, which altered the direction of RCOF by reducing the medial–lateral component. These results have implications for designing rungs with good friction in multiple directions and the potential for body position monitoring in ladder tasks.