Biomechanical response to ladder slipping events: Effects of hand placement

Ladder falling accidents are a significant, growing and severe occupational hazard. The factors that contribute to falls from ladders and specifically those that influence the motor response from ladder falls are not well understood. The aims of this research were to determine the effects of hand placement (rung versus rail) on muscle activation onset and peak activity timing in response to slipping on a ladder and to sequence the timing of events following slip initiation. Fifteen unexpected slips from 11 experienced ladder climbers were induced with a freely spinning rung under the foot, while subjects were randomly assigned to a rung versus rail hand grasping strategy. EMG onset time and peak activity time from five bilateral muscles (semitendinosis, vastus lateralis, triceps, biceps and anterior deltoid) were analyzed. Results indicated that significantly slower muscle activation onset and peak response times occurred during rail hand placement, suggesting that grasping ladder rungs may be preferable for improving the speed of the motor response. The triceps muscle activated and reached peak activity earlier in the slip indicating that subjects may initially extend their arms prior to generating hand forces. The study also revealed that slips tended to occur around the time that a foot and hand were in motion and there were just two points of contact (one hand and the slipping foot).