Figure 3
![Figure 3](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1757-1146-2-22/MediaObjects/13047_2009_Article_96_Fig3_HTML.jpg)
Arch index. Footprint with reference lines for calculating the arch index. The length of the foot (excluding the toes) is divided into equal thirds to give three regions: A – forefoot; B – midfoot; and C – heel. The arch index is then calculated by dividing the midfoot region (B) by the entire footprint area (i.e. Arch index = B/[A+B+C]).