## 2 Materials and Methods
### Podoscope Examination  
A 2D digital podoscope examination was performed, which consisted of scanning the feet and obtaining a digital image. Using Podoscan 2D (Sensor Medica, Guidonia, Italy), precise footprints of the subjects were obtained. With the use of the FreeStep Professional software v.1.3.01, the parameters for both feet were then determined on the resulting image. The 2D digital podoscope is an advanced analysis tool for footprints, foot geometry, and foot loading.  
After scanning, the length and width of the foot and the length of the medial longitudinal arch (cm), as well as the heel angle \(\gamma\) (\({}^{\circ}\)), were obtained and further analyzed.  
The Clarke index (CL) and Sztriter-Godunow index (KY) were used to assess the longitudinal arch, while the Wejsflog index (W) and heel angle (\(\gamma\)) were used for the transverse arch. Moreover, the hallux valgus (angle \(\alpha\)) and varus of the fifth toe (angle \(\beta\)) were measured (Figure 1).  
The Clarke angle (CL) is determined by the line C\({}^{\prime}\)-S\({}^{\prime}\) (the tangent to the medial edge of the foot) and the line passing through the point Q\({}^{\prime}\) (the point of the deepest depression) and C\({}^{\prime}\) (the point where the medial tangent meets the edge of the foot). (Figure 1: in the classification of feet according to the CL index, a flat foot was diagnosed in the range of x--30\({}^{\circ}\), a foot with a reduced arch 31-41\({}^{\circ}\), a normal foot 42-54\({}^{\circ}\), and a hollow foot (with an increased arch) in the range of 55\({}^{\circ}\)-x.)  
Figure 1: Graphical visualization of the determined parameters: Clarke’s index (CL), Sztriter–Godunow index (KY), Wejsflog index (W), heel angle (\(\gamma\)), hallux valgus angle (\(\alpha\)), and varus of the fifth toe (\(\beta\)).  
The Sztriter-Godunow index (KY) determines the ratio of the length of the segment running in the center of the arch of the longitudinal arch (W-I) to the length of the segment drawn by the adjacent and non-adjacent part of the scanned plantar surface of the foot (J-I), perpendicular to the medial tangent (Figure 1). Determining the KY index allows to establish the diagnosis depending on the value obtained, respectively: KY = 0.00-0.25--hollow foot; KY = 0.26-0.45--normal foot; KY = 0.46-0.490--reduced foot I\({}^{\circ}\); KY = 0.50-0.75--reduced foot II\({}^{\circ}\); and KY = 0.76-1.00--flat foot.  
The Wejsflog index (W) is the ratio of the length (AB) to the width of the foot (CD) and determines the degree of transverse arching of the foot (Figure 1). The length to width ratio of the foot should be 3:1; however, in practice, the values of the Wejsflog index are in the range of 2 < W < 3. Values closer to 2 indicate transverse flat feet, while values closer to 3 prove the correct transverse arch of the foot. Based on the data from the literature, the borderline value of a transversely flat foot was assumed to be 2.55.  
The calcaneal angle (\(\gamma\)) is determined by two tangents to the medial and lateral edges of the foot (Figure 1). The lines forming the angle \(\gamma\) intersect beyond the heel. The norm for the \(\gamma\) angle is 15-18\({}^{\circ}\) and it is assumed that values above 18\({}^{\circ}\), similarly to lower values of the W index, indicate transverse flat feet.  
The hallmark valgus angle (\(\alpha\)) is between the tangent to the medial edge of the foot and the tangent from the point at the widest point of the forefoot (the area of the metatarxophalangeal joint of the first toe) to the most medial point on the edge of the big toe (the area of the interphalangeal joint) (Figure 1).  
The varus angle of the toe V (\(\beta\)) is contained between the tangent to the lateral edge of the foot and the tangent from the point at the widest point of the forefoot on the outside (near the metatarxophalangeal joint of the toe V) to the most lateral point on the edge of the toe V (area of the interphalangeal joint proximal finger V) (Figure 1).