Fig. 3. Double logarithmic plot of the net energy cost of walking versus body mass (calculated from the subtraction method; see Materials and methods). The shaded circles represent human data from 20 previously published sources (calculated from the subtraction method, see Materials and methods) (Table 2), and the solid circle represents the mean value from these studies. The solid diamonds represent the other animals (see Table 4) used to generate the allometric equations for the net cost of walking. The solid line represents the predicted net cost of walking from the allometric equation based on animals for which either a minimum net cost of walking could be assessed or for which the net cost of walking was measured at a self-selected walking speed (E_walk; Eqn 4). The broken line represents the predicted net cost of walking from the allometric equation based only on animals for which a minimum net cost of walking could be assessed (E_walk,min; Eqn 3).