Engel and Staheli in 1974 (75) proposed the Staheli’s Arch Index (SAI) (Figure 2.4) determined by ratio of minimum width of midfoot area (A) to maximum width of hindfoot area (B). Equation of SAI is calculated by the following; SAI = A / B. In infancy, SAI for high arch is less than 0.70, normal arch is between 0.70 to 1.35, and low arch is greater than 1.35. In adulthood, SAI for high arch is less than 0.30, normal arch is between 0.30 to 1.0, and low arch is greater than 1.0.