The scaling of efficiency (<i>E</i>_{mech, CM}/<i>E</i>_met) against body mass in terrestrial locomotion.

<p>(A) The scaling relationships for all data grouped (solid line) and for the two size classes (dashed lines). Triangles are species with <1 kg body masses <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0006927#pone.0006927-Heglund1" target="_blank">[3]</a> and squares species>1 kg <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0006927#pone.0006927-Cavagna1" target="_blank">[6]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0006927#pone.0006927-Cavagna2" target="_blank">[7]</a>. Data points for <i>Macropus rufus</i> are labelled with <i>mr</i>. Individual trend-lines are for all data grouped; <i>y</i> = 0.10<i>x</i>^{0.27 (0.13–0.41)}, <i>t</i> = 4.11, <i>n</i> = 13, <i>r</i>² = 0.61, <i>p</i><0.05; species<1 kg, <i>y</i> = 0.07<i>x</i>^{0.16 (−1.30–1.613)}, <i>t</i> = 0.34, <i>n</i> = 5, <i>r</i>² = 0.04, <i>p</i>>0.05; species>1 kg, <i>y</i> = 0.26<i>x</i>^{−0.06 (−0.48–0.355)}, <i>t</i> = −0.36, <i>n</i> = 8, <i>r</i>² = 0.02, <i>p</i>>0.05. (B) Hypothetical step-change relationship between efficiency and body size. At some point within the size range depicted by the dotted lines efficiency may shift from 7% to 26%.