surface length (i.e., the hypotenuse of the triangle of which h is the
height and x is the base.), K was the time cost (Eq. (2)), and the
coefficients for the function were determined by collecting data
from ten separate walks with a total of 100km in length (Rees,
2004). Time cost function (K) can also be regarded as the walking
distance divided by the walking speed. The functions used in this
study are specified below as Eq. (1) to Eq. (3).