 The visualization of such an optimization for walking speed, cadence, and step length can be expressed in the form of a contour map, in which parameter combinations that lie on the same contour line share the same cost of transport (cal/kg/m).The green, red, and blue, dotted lines represent values where cadence, walking speed, and step length are constrained, respectively.These lines can be formed by finding the tangent points that lines representative of several constant parameter values form with the constant COT contours.