Validation of trip-induction system on a treadmill by comparison with a walking lane

Trip-related falls, which account for a significant portion of falls by the elderly, often result in serious injury. A method to evaluate fall risk accurately will be increasingly required in the aging society. For this purpose, it is necessary to analyze the natural reaction motion against tripping. We therefore developed a device and method to induce tripping at an arbitrary time during walking on a treadmill. To evaluate the validity of that method, another experiment that induced tripping on a walking lane was conducted. The reaction motions in the two environments were then compared. In this study, we focused on the difference in the preferred walking speed between the ground and the treadmill. The results suggest that the joint patterns during the reaction motion become similar when the subjective velocities, not the physical velocities, become the same for the subject, whereas physical parameters such as the trajectory of the center of mass become similar when the physical velocities match. These results help to understand the reaction motion against tripping and to reproduce the natural reaction motion on the treadmill.