2.2.1. Ink-Type Footprint Printer

According to the method proposed by Cavanagh in 1987, the subjects stood statically with even force on the ink-type footprint printer, then the subjects' footprints were obtained on the paper by the ink [6].

The measured footprint was drawn from the second metatarsal bone to the center of the heel, which is called the foot axis. Next, the foot axis was divided vertically into three equal parts, namely the forefoot (A), the midfoot (B), and the hindfoot (C) (Figure 1). The AI was calculated by the midfoot area (B) being divided by the full foot area (A + B + C). If the AI was less than or equal to 0.21, it was regarded as high arch; if the AI was between 0.21 and 0.26, it was regarded as normal foot; if the AI was greater than 0.26, it was regarded as flatfoot [6].

**Figure 1.** Ink-type footprint printer (**a**,**b**) the method of arch index calculation [6].
