Natural human suspension system with its applications

Abstract

Our ancestors first started to walk at least four million years ago; two million years later, they learned how to run. Unfortunately, they could only run barefooted at the time, as the first shoe was not invented until around 40,000 years ago. It is natural for human beings to try to avoid injuries. In earlier times, most runners hit the ground first with the front part of the foot, i.e. with a fore-foot strike (FFS) pattern. After the invention of modern running shoes in the 1970s, most runners today choose to hit the ground first with their heels, i.e. with a rear-foot strike (RFS) pattern. Since the 1980s, participation in running activities has surged, and many runners without proper training often suffer from injuries. Studies show that 70 percent of runners experience injuries at least once a year. This study aims to understand the causes of different injuries and to explore ways to prevent and reduce the injuries experienced in different human postures, e.g. standing, sitting, walking, and running. Human-involved indoor experiments and computer-based simulations were conducted. A group of 35 volunteers without any open wound or history of significant injury during the past six months were asked to perform on an EVA foam runway. The newly-defined natural foot strike (NFS) pattern was introduced and assessed along with FFS and RFS patterns. Participants’ kinetic and kinematic performances were measured by a force distribution measurement (FDM) system and a motion capture system and were analysed by the zebris FDM software. For sitting postures, thanks to the invention of inerter, a new kind of passive mechanical element, the performance advantages of different vessel models were compared and analysed by the MathWorks Matlab software. During the indoor experiments, subjects with varying foot strike patterns demonstrated different timing of impact to the lower limbs and different ground reaction forces. Compared with RFS and FFS patterns, the NFS pattern showed later transient peaks of ground reaction forces, fewer appearances of the second transient peaks, and smaller ground reaction force under the ball and the heel of the foot. The simulations of the vessel’s passive suspension system illustrated reduction of disturbances under heave motions and heave acceleration within the lower frequency range. The NFS pattern could reduce runners’ injury risk in both shod and barefoot conditions. The combination of inerters with springs and dampers could help the passive suspension system damp out the wave disturbances applied to a well-developed vessel model. An alternative view of understanding the relationship between different human postures and their injuries was proposed and verified by experiments and simulations. The current research findings have a wide range of potential applications. It can help runners and workers avoid injuries by adding the foot strike patterns and the layout of passive suspension systems. The recovery of amputees’ walking capability can be improved by introducing a bio-inspired artificial foot or lower limbs with specific mechanical settings. Furthermore, the angle-adjustable robotic foot with varying suspension layouts can make humanoid robots more human-like.