Fig. 6. Differences (a-b) in metabolic rate (CO₂ release) between running on (a) inclines of -60° (A), -30° (B), 30° (C), 60° (D) and (b) level walking. Differences are plotted as a function of running speed of the animal over ground and derived from the mean values for each speed bin (see Fig. 4). Dotted lines indicate both equal metabolic costs between inclined and level walking (horizontal line), and 90 mm s^-1 walking speed (vertical line), which was the maximum speed used for linear regression fits. Values are means ± S.E.M.