Slip-related falls can be induced by instability or limb collapse, but the key factors that determine these two fall causations remain unknown. The purpose of this study was to investigate the factors that contribute towards instability-induced and limb-collapse-induced slip-related falls by investigating 114 novel slip trials. The segment angles and moments of the recovery limb after slip-onset from pre-left-touchdown (pre-LTD) to post-left-touchdown (post-LTD) were calculated, and logistic regression was used to detect which variable contributed most to instability-induced and limb-collapse-induced falls. The results showed that recovery from instability was determined by the angle of the thigh at LTD (87.7%), while recovery from limb collapse was determined by the angle of the shank at post-LTD (90.4%). Correspondingly, instability-induced falls were successfully predicted (81.5%) based on the initial thigh angle at pre-LTD and the following peak thigh moment, while limb-collapse-induced falls were successfully predicted (85.5%) based on the initial shank angle at LTD and the following peak shank moment. According to our findings, taking a shorter recovery step and/or increasing the counterclockwise moment of the thigh after pre-LTD would help individuals resist instability-induced falls, while taking a larger recovery step and/or increasing the clockwise moment of the shank post-LTD would help resist limb-collapse-induced falls. The findings of this study are crucial for future clinical applications, because individually tailored reactive balance training could be provided to reduce vulnerability to specific types of falls and improve recovery rates post-slip exposure.
Keywords: Instability; Limb collapse; Recovery step; Segment moment; Vulnerability.