The energy function developed by Minetti et al. (2002) was
selected in this study due to its simplicity of use. Energy cost here
is referred to the consumption of physical activity. Energy cost
was calculated by a fifth-order function, and the function used
the gradient i as a parameter. The gradient i represented slope
defined as dh/dx where h was the height and x was the walking distance.
The function describing the relationship between Cw (Unit:
Joule·Kilogram−1·meter−1) and gradient i at slope ranging from
−45% to +45% was performed as