Fig. 5. (A) Increases in negative external mechanical work rate (black circles) and (B) net metabolic rate (black circles) were both dominated by the fourth power of step length l. External mechanical work rate (A) is compared against a nonlinear regression from Equation 3 (black line), and metabolic power (B) is compared against a regression from Equation 4 (black line). Note that traditional combined limbs measures of total negative external mechanical work rate (grey circles in A) underestimated the external work rate generated by the individual limbs. Values shown are means ± S.D., N=9. l^*, preferred step length; C,C', D,D', constants. See Materials and methods for details.