Fig. 5. Results of spontaneous gait selection parameters (data points) compared to minimum metabolic cost as predicted by the constrained optimization hypothesis. In each case the predictions are shown as a range around the tangent point indicating cost minimization for that constraint, where red indicates ±1%, orange ±5%, yellow ±10% and gray bounded by black ±15%. Mean for each constraint is indicated by a solid black circle with error bars showing ± 1 S.D. The data points for speed and step length constraints are fit with a power function (solid black line) with the constraint as the determinant variable (see text for details). For the frequency constraint (B) regressions of those subjects that chose the higher speed (long dashes) and lower speed (short dashes) options are also indicated. For all frequency constraint regressions a simple quadratic was used. Metabolic cost contours used to derive the constrained optimization predictions are shown in blue for reference. Data points are plotted in colors associated with the particular constraint applied, as in previous figures.