Fig. 8. Net metabolic rate _met exhibited a U-shaped curve as a function of arc radius . For small radii, metabolic rate decreased with much as predicted by the Simplest Model (Fig. 2). However, metabolic rate reached a minimum at =0.30 according to the Empirical Fit of Eqn 11, r²=0.86, and began to increase with larger . The energetic cost of walking was 59% higher than the minimum for the smallest arcs, and higher for all arc radii compared to normal walking (broken line). Different coloured symbols indicate different subjects.