Individual movement strategies in response to an external force

Density, velocity, or flow are key quantities to describe dense crowds. However, they neglect the 3-dimensional movements of a person. Although methods exist to describe the motion of a single individual, it is difficult to determine individual movements within a group and which particular singular actions may pose risks to others.To explore how people react when being pushed, experiments that focus on individual movement strategies and interactions in response to an external force were carried out. Participants were lined up in a queue and the person at the end of the row was pushed forward in a controlled manner. Variations included the intensity of the push, the distance between the participants, and the time between the positioning and the push. During the experiments, 3D motion profiles using motion capturing suits were obtained and the head trajectories of the participants were recorded. In addition, pressure sensors were used to quantify the intensity of the pushes by measuring the normal force on the sensor surface. As a first step, movement strategies for regaining balance were identified by a qualitative analysis of the videos. We could distinguish three behaviours: They are (i) walking forward in an upright posture, (ii) pushing off with arms after a pendulum movement, and (iii) leaning backwards. The main difference is whether the push is passed on in the row or participants attempt to absorb the push. In a next analysis, the motion types will be quantified using the 3-dimensional movement data. Possible metrics for this include the position of the hip relative to the upper trunk, the displacement angle of the upper trunk, or the step width. Furthermore, the influence of different factors such as body size, position in the row and intensity of the push on the strategies used will be investigated. It will also be analysed how far the push is passed forward through the row as well as the effects of the push to the side when people are standing in a group