Foot-body coupling angle is a strong kinematic predictor of friction requirements during ladder descent: Implications for slipping risk

Abstract

Slips and falls from ladders are a common cause of workplace injuries, yet insufficient research explains the cause of these incidents. This study identifies the association between the required coefficient of friction (RCOF) and biomechanical factors (foot angle, body angle, foot-body coupling angle, foot contact velocity, foot placement, and trunk center of mass velocity) during ladder descent. In bivariate regression analyses with the ladder angle as a covariate, foot angle was negatively associated with RCOF (i.e. toe-down has a higher RCOF) (t₃₆₂ = −19.8, p < 0.001). The body angle was negatively associated with RCOF (i.e. aligning the center of mass above the foot has a higher RCOF) (t₃₂₃ = −3.4, p = 0.001) and there was a positive association between the foot contact velocity and the RCOF (t₃₅₉ = 5.2, p < 0.001). Additionally, there was a strong association between the foot-body coupling angle and the RCOF (t₃₂₃ = 21.8, p < 0.001, R² = 0.606) in which the ladder angle had a small effect. A multivariate model supported that both the foot (t₃₂₂ = −21.3, p < 0.001) and body angle (t₃₂₂ = 8.2, p < 0.001) independently contributed to the RCOF, which supported the validity of the foot-body coupling angle. This work indicates that the foot-body coupling angle is a compelling metric associated with RCOF and could be used to train safer climbing techniques and monitor behavior to reduce ladder slip and fall events.