The tribologists from the Institute of Problems in Mechanical Engineering of the Russian Academy of Sciences have studied the specifics of biomechanics of the frictional interaction of the foot with the supporting surface and their effect on the stability of the bipedal walking process, that will help in creation of innovative orthoses and prostheses in the future.
The scientists of IPMash RAS made a report on the results of their work «Canonical Patterns of Impact-friction Interaction of a Foot with a Supporting Surface» in Perm at the International Conference on Biomechanics, and also published an article in the scientific journal Priborostroyeniye (Instrument Engineering).
Studying the patterns of foot reactions during standard bipedal walking plays a key role in understanding the human biomechanics. These data make it possible not only to simulate the walking process correctly, but also to create more advanced prostheses. The analysis of load distribution, dynamics of contact with the supporting surface and foot adaptation to various conditions opens up new opportunities in robotics, prosthetics and rehabilitation medicine.
The aim of the research by IPMash RAS scientists was to find out the key patterns of interaction of the foot with the supporting surface, including the analysis of forces, moments and deformations at different phases of a step. The results obtained will form the basis for the development of an ergonomic ankle-joint orthosis, which should provide optimal support, reduce tiredness and minimize the risk of injury.

“Experiments on motion capture were conducted and the kinematics of the musculoskeletal system was investigated. The dynamometric platform was used to determine the normal and tangential reactions of the foot with a static approach to calculation. In the development of the dynamic approach, the author's MEMS accelerometers were tested to study shock interactions recorded in fractions of free fall accelerations. This approach allowed us to reveal for the first time that shock impulses during walking are localized at three points of the foot (heel and metatarsals of the thumb and little finger), and not at two points (heel-toe) as was assumed previously”, — said Viktor Musalimov, IPMash RAS Chief Research Scientist.

To study the friction forces and impacts, which occur when walking, the researchers applied special mathematical functions (Hermite functions) which helped to simplify the analysis. They also changed over to dimensionless quantities, that revealed clear relationships. It turned out that longitudinal friction (sliding) and transverse friction (spinning) are related by mathematical equations. In addition, the scientists found out that, when walking, the foot of the free leg fluctuates in a special way, ensuring the stability of the bipedal walking process. But the support foot in the rolling phase moves along a trajectory resembling a «snake», which can be described using the model of a deformable elastic spiral-anisotropic cylinder. These results help to understand better the mechanics of walking and may be useful in the development of robots, orthoses and orthopedic devices.

In the future, it is planned to improve the design of the ankle-joint prostheses, to develop a mechatronic system for controlling its stiffness and friction in friction units (including interaction of the structure with the skin), as well as to create a remote system for monitoring the condition of the entire device.