The effect of arm posture and descent height on landing forces

Abstract

Operators of mobile construction equipment (e.g., bulldozers, scrapers, etc.) often opt to descend out of the cabin in an irregular fashion without using proper egress methods, despite being trained on proper egress methods. The main objective of this research was to quantify and compare the effect of arm posture, landing style, and descent height on ground reaction forces, and acceleration at the ankle and knee by performing a laboratory study. Fifteen male subjects descended from three different descent heights (38.1, 50.8, and 63.5cm) using three different arm postures (arms to the side, arms front, and arms crossed) and landing on both legs at the same time, right leg first, and left leg first. The results demonstrated that with the increase in descent heights, the ground reaction forces, and accelerations at the ankle and knee increased. Landing with the arms out stretched horizontally in front of the body (arms front) resulted in higher ground reaction forces, peak resultant acceleration at the knee, and higher transmissibility between the ankle and the knee compared to the arms hanging to the side of the body. Although having the arms out front when landing may slightly reduce impact forces, this posture may help in maintaining balance upon landing. Landing with “both legs at same time” increased the GRF, whereas landing on one leg first followed by the other leg seemed to distribute the landing force over a longer period of time. Landing on one or two legs at the heights tested in this study resulted in ground reaction forces lower than injury threshold values for the ankle from previous research. However, descending from higher heights may result in impact forces approaching or exceeding injury threshold levels. Results from this study on the effect of arm posture and landing style may be helpful for training OE on egress at lower level heights, however, engineering controls may be needed at higher egress heights.