Analysis of upper extremity motion during trip-induced falls

Abstract

Forward fall is one of the most common causes of upper extremity fractures. Significant factors influencing impact force and injuries were widely studied; however, it is necessary to investigate the natural reactions of humans during a forward fall to obtain a realistic evaluation of injuries. The purpose of this study was to analyze the natural motion of the upper extremity during an induced trip. We carried out a tripping experiment using an obstacle colliding with one leg; while recovery step was prevented to produce a forward fall. Results showed that the elbow extension had a slight ascending trend during the forward fall and elbow angle at the moment of hand-ground contact was appropriate to reduce the peak force. Landing on the obstacle-side hand was more likely due to body rotation towards the obstacle-side. To prevent injuries, subjects were connected to a safety harness not to strike the ground with high impact velocity. Thus, the fall motion was simulated using a 12 DOF model to obtain a realistic evaluation of the impact velocity and the related impact force caused by the forward fall was estimated using a sagittal 3-segment model. Results of this study can be useful in human-robot collaboration, where a collision between human and robot may cause a forward fall.