## 2 Materials and Methods
### The Main Parameters Concerning the Analysis of the Ground Load of the Body Weight Through the Foot  
The biomechanical system of the foot is influenced by two centres of gravity, \(CoG_{1}\) and \(CoG_{2}\). \(CoG_{2}\) is a point that concentrates the weight of only that part that is tilted on the axis of rotation (the upper ankle joint in the case of humans), which is important in the analysis of gravitational torques and counteracting muscle torques [13; 14]. In the calculation of the \(CoG_{2}\), the body weight does not include the human lamina pedis, because it is a platform on which the rest of the human body is supported. \(CoG_{1}\) (general centre of gravity) is the point where the weight of the entire object (\(W_{CoG1}\)) is concentrated, including the weight of the support platform (in the case of humans, the foot). The value of the general weight concentrated in \(CoG_{1}\) affects the load of the ground with the body weight through the foot.  
For ease of consideration, the manuscript considers the load of one foot with the entire body weight. In the case of the analysis of bipedal stance, the obtained results should be divided by two to obtain the load of each foot.  
The two support points in the platform, that is, the feet, are taken into account. The first is localised on the forefoot on the most peripherally protruding part, which is the head of the first metatararsal bone (point \(A\)). The second one is localised on the most posterior part of the hindfoot, which is a calcaneal tuberosity (point \(B\)) (Figure 1). The body can lean forward and backwards, maintaining balance only to the limit of the projection of \(CoG_{1}\) falling on the anterior support point (point \(A\)) in the case of a forward body lean and on the posterior support point (point \(B\)) in the case of a backwards lean. The distances between the extreme support points \(A\) and \(B\) and the projection of the general centre of gravity \(CoG_{1}\) are shown in the figure (Figure 1A,B).  
Given the above parameters and using the principle of rotational moment balance for a two-supported beam (1) (2), the position of the general projection of the centre of gravity (\(CoG_{1}\)) on the support platform was determined. With the known load of points, \(A\) and \(B\) (\(W_{A}\), \(W_{B}\)) obtained by measuring the load on scales and the known distance between points \(A\) and \(B\) (\(r_{D}\)), the distance from point \(A\) to the line of the general projection of the centre of gravity (\(r_{A}\)) (3) and the distance from point \(B\) to the line of the general projection of the centre of gravity (\(r_{B}\)) (4) were calculated (Figure 1A,B).  
Figure 1: Diagram of the ground load of the body weight (\(W_{CoG1}\)) through the foot in the general body centre of gravity \(CoG_{1}\) inclination (including the support platform). (**A**) \(CoG_{1}\) deflection forward, (**B**) \(CoG_{1}\) deflection backwards. (**C**) Diagram of the human body with the general body centre of gravity (\(CoG_{1}\)) and body weight symmetrically distributed on two feet. In a standing position on both feet, the load on each foot is equal to half the body weight value. \(A\)—front support point, \(B\)—rear support point, \(W_{A}\) and \(W_{B}\)—load on the front (\(A\)) and rear (\(B\)) support points, respectively, \(W_{I}\)—resultant of the forces of gravity \(W_{A}\) and \(W_{B}\), \(W_{B}\)’—vector parallel to \(W_{B}\) with the same value, \(\gamma\) [\({}^{\circ}\)]—the angle between the vector \(W_{A}\) and \(W_{B}\)’ lying opposite the vector \(W_{I}\), \(r_{CoG1}\)—the arm of the gravity force of the general centre of gravity \(CoG_{1}\), \(r_{A}\)—distance from point \(A\) to the projection of \(W_{CoG1}\) on the support platform, \(r_{B}\)—distance from point \(B\) to the projection of \(W_{CoG1}\) on the support platform, \(r_{D}\)—distance from point \(A\) to \(B\), grey point with a cross – axis of rotation in the upper ankle joint.