Fig. 6. Correlation between mechanical step-to-step transition costs and metabolic costs for varying step lengths. One estimate for step-to-step transition costs (open circles) is found from negative external mechanical work rate; a least-squares linear regression of these data exhibits linearity (broken line, r²=0.89). This is probably an overestimate because it fails to attribute some of the increases in power to leg motion. A lower bound on step-to-step transition costs (solid circles) is found by correcting for the contribution due to leg motion, C_legl² (Equation 3); a least-squares linear regression of these data also exhibits linearity (solid line, r²=0.79). These data are for step lengths l^* in the range (0.6-1.4l^*).