Inverse dynamics and ground reaction force estimation during walking

This paper looks into the forces applied to the joints, and the ground reaction forces (GRFs) during walking. In this vein, inverse dynamics of a human being are studied by considering a 3-dimensional, 7-link dynamic model which has 18 degrees of freedom. During the double-support phase in which both feet are in contact with the ground, the distribution of the GRFs over the two feet is a result of the person´s gait of walking, and various environmental conditions. Therefore, one can only obtain the total force applied to both feet in each direction and not the distribution of GRFs over the two feet. Specifically, in this phase we are faced with an indefinite problem, which should be solved by considering some extra assumptions. In this paper, for developing a completely theoretical model which has a good agreement with the reality, extra assumptions are developed, inspired by some experimental results. Within this framework of assumptions, the inverse dynamics problem is solved in the single and double support phases, by which the joint forces (especially the hip joint) during walking can be calculated. The analytic results are then compared with the experimental results, leading to a modified approach. In this way, a method for calculating the joint forces and the GRFs, independent of the experimental tests, is developed.